Aquafaba Meringues

Photo credit: veganbaking.net (vegan-baking/Flickr)

Photo credit: veganbaking.net (vegan-baking/Flickr)

Dr. Kent Kirshenbaum flew from NYC to LA to speak at our March 8th public lecture about the impact of what we eat, sharing the stage with Dr. Amy Rowat, Dr. Paul Thompson, and Chef Daniel Patterson. Impressively he brought along with him a case of hundreds of homemade vegan meringues for lecture attendees to nosh on after the event.

In lieu of egg whites, the meringues contained aquafaba, the liquid from canned chickpeas. To the surprise and delight of Science & Food guests, the airy confections were devoid of any chickpea flavor. Some reached for seconds (or guilty thirds) while others wondered how Dr. Kirshenbaum was able to transport the fragile cookies across the country without any of them breaking. (Note from backstage: all the cookies were in mint condition when we received the case from Dr. Kirshenbaum–until moments before the event when one of us volunteers fumbled during setup and dropped one. Oops!)

Whether you want to recreate Dr. Kirshenbaum’s aquafaba meringues because you loved them so much or you couldn’t make the event, we have the recipe below!

A Science & Food volunteer offers lecture attendees Dr. Kent Kirshenbaum's amazing vegan meringues.

A Science & Food volunteer offers guests Dr. Kent Kirshenbaum’s amazing vegan meringues.
Photo credit: Abbie F. Swanson (@dearabbie/Twitter)

Aquafaba Meringues

1/2 to 3/4 cup of liquid drained from a 15 oz can of chickpeas
1/2 cup sugar

1. Preheat oven to 215 °F.

2. Using an electric mixer, beat the canned chickpeas liquid at high speed until stiff peaks form.

3. Once peaks have formed, add sugar one tablespoon at a time. After all the sugar is incorporated, if the foam feels gritty, keep whipping until the mixture is smooth.

4. Spoon or pipe the meringue in 1.5 inch dollops onto parchment paper-lined baking sheets.

5. Bake at 215 °F for 1.5 hours.

6. After baking, turn off the oven and crack the oven door open to allow the cookies to cool to room temperature. Store cookies in an airtight container.


Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


The Science of Sous Vide

“Sous vide,” or “under vacuum,” refers to a style of cooking in which food is sealed in a plastic bag and submerged in a water bath that is held at a controlled temperature [1]. This technique originated in ancient times when humans wrapped their food in salt, fat, animal leaves, and animal bladders before cooking [2]. Sous vide in its fully realized form began in the 1960s as NASA scientists began to incorporate this concept into creating astronauts’ sealed-bag meals [2]. In the 1970s, French chefs (who had already popularized cooking en papillote or in paper), adopted the sous vide technique of cooking in plastic [3]. From here, sous vide spread to professional kitchens across the world, but it was not until the 1990s that food scientists began to study the deeper science behind sous vide processing. By the mid-2000s, sous vide became widely known and the past decade has seen a massive increase in its popularity [1] where it is heralded as “the most important technological advance in the kitchen since the microwave.” [3] Before sous vide machines were accessible to the home chef, a common method was using an ice chest, which keeps water hot long enough to effectively sous vide food [4]. Although this is still a popular and inexpensive technique, sous vide machines are now available from many brands for under $200.

Traditionally cooked steak (left) vs. sous vide steak (right). The gradation is very visible in the traditionally cooked steak. Photo credit: Nathan Myhrvold/Modernist Cuisine

Traditionally cooked steak (left) vs. sous vide steak (right). The gradation is
very visible in the traditionally cooked steak. [Photo credit: Modernist Cuisine]

The appeal of sous vide comes with its ease and ability to precisely control the temperature at which the food is cooked. By targeting a specific minimum temperature at which proteins denature, it is virtually impossible to overcook your food. When food is cooked by traditional methods such as on the stovetop or in the oven, the outside of the food rises to temperatures that are much higher than the final desired temperature of the food. This increases the risk of overcooking the outside (and inside) of the food in an attempt to reach the correct internal temperature. By using sous vide, food is cooked for a longer period of time and at a lower temperature than usual and is raised uniformly to the same temperature [5]. This prevents evaporative loss of moisture (Fig. 1) and enables tough cuts of meat to be made tender while still cooking them medium/medium-rare [1].

Figure 1: The weight loss (moisture loss) from New York strip steak at varying temperatures ranging from 120-160°F [6].

Figure 1: The weight loss (moisture loss) from New York strip steak at varying temperatures ranging from 120-160°F [6].

Another advantage to sous vide is from a nutritional standpoint. Sous-vided vegetables retain their vitamins and trace elements; by contrast, boiling removes 60% or more of these nutrients [3]. Sous vide also requires little added fat (oils, butter, etc. are usually added solely for flavor). Additionally, because the food is sealed in a plastic pouch, this largely reduces oxidation and therefore preserves the nutritional qualities of polyunsaturated fatty acids [7]. Lastly, because food can be cooked at lower temperatures, the vitamins that are normally destabilized at the high temperatures of traditional cooking methods are preserved [8].

While this effective technique was formerly limited to professional kitchens, it is now accessible for the home cook! Companies such as Anova, Nomiku, and Sansaire have recently developed sous vide machines at an attractive price point. Fascinated by the attention around this rapidly popularized method, I purchased my own Anova and set out to test to see if these sous vide machines lived up to the stories.

At-home immersion circulators from different popular brands. Photo credit: Modernist Cooking Made Easy

At-home immersion circulators from different popular brands. [Photo credit: Modernist Cooking Made Easy]

The first beast I tackled was the one I have always had a penchant for overcooking – the New York Steak. No matter what technique I tried to use, I always end up oversearing and getting a ring of medium-well steak around my perfectly medium-rare center. Using one of my favorite sites for recipes, Chef Steps, I attempted their Simple Sous Vide Steak with Red Wine Sauce. I pre-seared my steaks (this gives you a better crust at the end of the cooking process), placed them in a Ziploc bag with some butter, and popped them into my preheated 135°F water bath. After an hour I removed the steaks and quickly seared them again to get a delicious golden brown crust. Result? Mouthwatering, juicy, tender steak with unbelievable flavor and a beautiful medium-rare interior that extended from edge to edge. Absolute gastronomic perfection.

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Results from my sous-vided New York steak. [Photo credit: Ashton Yoon]

Thrilled with the results of my first experiment, I tackled a variety of other proteins and the results of these attempts are shown below. Salmon was so simple: a quick 20 minutes at 126°F yielded the most buttery salmon I had ever tasted, with a compelling sashimi-like texture.

Photo credit: Ashton Yoon

Salmon in brine (left) and finished sous vide salmon with lemon wasabi aioli, recipe from Sous Vide Supreme (right). [Photo credit: Ashton Yoon]

sousvide6

Pork belly immersed in the water bath (left). Honey sriracha pork belly with carrot purée, salsa verde, and pickled radishes. Recipe inspired from the 2014 movie “Chef” (right). [Photo credit: Ashton Yoon.]

New Zealand rack of lamb with herb crust during the cooking process (left). Final product, lamb recipe from Epicurious and Hasselback potato recipe from The Kitchn. Photo credit: Ashton Yoon.

New Zealand rack of lamb with herb crust during the cooking process (left). Final product, lamb recipe from Epicurious and Hasselback potato recipe from The Kitchn. [Photo credit: Ashton Yoon.]

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Eggs during the sous vide process, no plastic sealing needed (left). Egg cooked at 155°F, recipe from Serious Eats (right). [Photo credit: Ashton Yoon.]

My impression of at-home sous vide? Stellar. Not only was the entire cooking process easy, but I was guaranteed to get perfect results every time. The flavors and moisture retention were incredible. And the added nutritional value is just the cherry on top of the already sweet, sweet cake.

References cited

  1. Baldwin, Douglas. “Sous Vide Cooking: A Review.” International Journal of Gastronomy and Food Science 2012: 15-30. Print.
  2. Myhrvold, Nathan. “Why Cook Sous Vide?Modernist Cuisine. Cima Creative, 2013. Web. 24 November 2015.
  3. Renton, Alex. “Sous Vide: The Chef’s Secret Coming to Your Kitchen.The Guardian. Media Limited, 2014. Web. 25 November 2015.
  4. López-Alt, J. Kenji. “Cook Your Meat in a Beer Cooler: The World’s Best (and Cheapest) Sous Vide Hack.Serious Eats. Serious Eats, 2010. Web. 2 January 2015.
  5. Suchy, Sara. “Testing Cooking Temperatures of Sous Vide.” Inside Science. American Institute of Physics, 2013. Web. 25 November 2015.
  6. López-Alt, J. Kenji. “How to Sous Vide Steak.” Serious Eats. Serious Eats, 2010. Web. 2 January 2015.
  7. Sasson, L. (2006). Functions of Fat Lecture, New York University.
  8. Buckley, C. (1987). “Storage stability of vitamin C in a simulated sous vide process.” Hotel and Catering Research Centre Laboratory Report 238: 2.

Ashton YoonAbout the author: Ashton Yoon received her B.S. in Environmental Science at UCLA and is currently pursuing a graduate degree in food science. Her favorite pastime is experimenting in the kitchen with new recipes and cooking techniques.

Read more by Ashton Yoon


Deep-fried Turkey: Delicious or Dangerous?

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Is a Deep-Fried Turkey your Destiny [Photo Credit: Jinx!]

While you may think the most dangerous thing you can do during the holidays is talk politics with your uncle, starting a kitchen fire is a more realistic threat to your safety. According to the United States Fire Administration (USFA), the number of structure fires double on Thanksgiving, causing on average $28 million in property damage1. Cooking causes the majority of these blazes, with grease and oil as the main culprits in ignition2. Despite the astonishingly large number of holiday mishaps, home cooks continue using fats. A select few even engage in one of the most daring of food adventures: deep-frying a turkey.

A quick Internet search for “deep-fried turkey” reveals how dangerous this culinary practice can be. There are plenty of videos and pictures that document the aftermath of a deep-fried turkey fire. A careless and unprepared chef can turn a deep-fried turkey into a deep-fried disaster within minutes. The bird quickly becomes engulfed in a fireball that can be seen from the rest of the neighborhood. So then, what makes deep-frying more appealing than roasting? More importantly, can it be done safely?

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[Photo credit: State Farm]

The key to effectively deep-frying a turkey is oil. Oil makes the bird both delicious and dangerous. Oil’s interaction with the poultry causes the characteristic crispy golden brown crust that draws people to deep-frying. This same oil, however, can ignite and cause a fire. To effectively and safely deep-fry a turkey, you must understand the science underlying deep-frying.

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Oil is the key to a Deep-Fried Turkey [photo credit: Joe]

The main appeal of a deep-fried turkey is the texture created by oil interacting with the bird’s skin. In deep-frying, hot oil completely engulfs the food. Put an uncooked turkey in hot oil and bubbles immediately start forming. The bubbles are not from the oil, but from the water within the surface of the bird that escapes as tiny pockets of steam. Water boils at 212 °F, but the temperature of oil in a deep fryer is typically around 350 °F or greater. Because of these high temperatures, the water in the turkey skin rapidly evaporates. This dehydration at the surface combined with the high temperature make conditions perfect for the Maillard reaction.

Maillard reactions create the characteristic deep browning and appealing aromas that you may have experienced when you deep-fry a turkey. These reactions typically occur when proteins and sugars in foods are exposed to high heat (284 – 329 °F): the amino acid building blocks of proteins react with sugars at high heat to create a complex set of flavor molecules. This is why a deep-fried turkey may evoke similar flavors and aromas as seared steak, roasted coffee, or toasted bread. As heat continues to vaporize the water on the bird’s skin, the reaction speeds up and the resulting flavor molecules become more and more concentrated.

While Maillard reactions can also be achieved through roasting a turkey, deep-frying avoids some of the pitfalls of oven roasting. First, because the hot oil completely envelops the bird, the outside gets an even brown coat. The temperature of the oil remains relatively constant as it spreads into every crevice. Such uniformity can be harder to achieve in traditional oven roasting, because of differences in air temperature within the oven. Moreover, poor heat circulation can result in uneven cooking. In extreme cases, you might find one side of the turkey charred, while the other is still undercooked.

Next, because the oil can transfer more heat than air per unit volume and time, deep-frying can allow the bird’s surface to get hot quickly enough so that the inside does not overcook. In deep-frying, oil acts as the workhorse transferring heat to food. By contrast, ovens rely on air to transfer heat. Compared to air, cooking oil has a much higher rate of heat conduction. Heat transfers between substances when the molecules collide and transfer energy. Because a liquid such as oil is more dense then air, its molecules are more closely packed; there are more molecules per volume to transfer energy. As a result, the high heat needed for the Maillard reactions develops much faster in a deep fryer than in the oven. In general, oven roasting generally takes about 2-4 hours, while deep-frying can take as little as 30 minutes. Slower increases in surface temperature, as in the case of the oven, allow for more time for the high heat to spread to the center of the turkey and overcook the inside.

Many deep-frying fans claim that the practice “seals in the juices”, however, internal temperature has a larger impact on moisture. If you’ve ever bit into a dry piece of fried chicken, you know, that deep-frying does not guarantee juicy poultry. Fans claim that oil creates a barrier to lock in moisture, but as previously highlighted, hot oil causes it to vaporize and escape. Even water near the interior can escape if it reaches the boiling point because the crust remains porous. The meat on the inside cooks in the same way as in roasting, but only faster because the oil transfers more heat. Thus, regardless of whether you deep-fry or roast the bird, you need to watch the internal temperature to get a juicy turkey.

While hot oil is essential for transforming your turkey into a delicious brown and crispy treat, properly controlling the oil will keep you safe. The first step is having the proper equipment. While a turkey can be deep fried in any number of large pots you already have, none of them are specifically designed to safely handle 3 gallons or more of hot oil and a giant turkey. Having a deep fryer specific for turkeys ensures that when you use the right amount of oil, the turkey is completely submerged and the oil won’t overflow. Also you can cook with a turkey deep fryer outside; this keeps the hot oil safely away from anything flammable in your home. So if you do make a mistake, it’s far away from anything that can spread a fire.

Next, to avoid turning the turkey into a giant fireball, it must be properly dried. This means checking that the bird is completely thawed and free of excess water. If too much ice or water remain, either can quickly vaporize causing oil to spray into the air. You may have seen a similar reaction occur when you throw drops of water into hot oil to test if it’s reached frying temperature. Sudden vaporization results in tiny droplets of oil spewing out in a fine mist. As microscopic droplets, the oil increases its chances of contacting the burner and reaching its flash point, or the temperature at which a material can ignite. (The flash point is around 600-700°F for many cooking oils.) In the deep fryer, oil won’t get as hot, but as droplets, oil can reach this temperature because of their small size and increased surface area. The ignition of a few small oil droplets can set off a chain reaction that engulfs the entire bird. This is why a seemingly innocent icy turkey can turn into a fireball.

Finally, you may want to consider that deep-frying adds a significant amount of fat to your bird compared to roasting it. The entire surface of the turkey is covered in oil and some may seep into the interior. In general, deep-frying can result in as much as 5 to 40% of a food’s weight in oil3. If you are concerned about your fat intake you might want to avoid this deep-fried treat. However, eating a deep-fried bird only on Thanksgiving likely won’t jeopardize your health too much.

Deep-frying a turkey requires significant culinary effort. Although this cooking method is potentially dangerous, your fowl can develop delicious flavors and aromas that cannot be achieved as quickly in the oven. Whether or not you want to make the investment ultimately depends on what you like about eating turkey. If you only care about juicy meat, then using an oven and monitoring the temperature can be easier. However, if you crave a truly unique treat encased in a crispy brown crust, then deep-frying a turkey may be your next gastronomic adventure.

References cited

    1. USFA. Thanksgiving Day Fires in Residential Buildings (2009-2011) http://www.usfa.fema.gov/downloads/pdf/statistics/snapshot_thanksgiving.pdf
    2. USFA. Cooking Fires in Residential Buildings (2008-2010) http://www.usfa.fema.gov/downloads/pdf/statistics/v13i12.pdf
    3. Owen R. Fennema, editor, Food Chemistry, 2nd Edition (New York: Marcel Dekker, Inc, 1985), 210-221

Vince ReyesAbout the author: Vince Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

Read more by Vince Reyes


Kombucha Brewing: The Process

Photo credit: Mgarten (Wikimedia Commons)

Photo credit: Mgarten (Wikimedia Commons)

At first glance, making kombucha sounds straightforward. After all, kombucha is fermented tea, which tells all you need to know about making it: take some tea and ferment it. Unfortunately, brewing kombucha is not that simple, as evidenced by the plethora of information and recipes found on the Internet. For those who have ever contemplated or even decided to begin brewing kombucha for the first time, don’t let the wealth of kombucha information intimidate you. Here, we break down the process of kombucha brewing and experimentation, supplying you with the scientific rationale for each step. Understanding the science of each stage may allow for a more successful and experimental brewing without having to rely on a recipe.

1. Making the tea base.

The tea base is nothing more than sweetened tea, so it is easy enough to make. However, the amount of tea and sugar used will affect the flavor of the resulting kombucha. The exact proportion of water to tea to sugar can be modified to suit personal tastes. For the varieties of teas and sugars suitable for making kombucha, check out our previous post on the ingredients that go into making kombucha.

In general, for every 1 cup of boiled water, steep 1 tea bag or 1 ounce of loose leaf tea; this should be left to steep for 3 – 5 minutes, with deviations depending on the type of tea and desired tea strength. Certain teas, such as green and white teas, have subtle flavor profiles that may result in a bland-tasting kombucha. To obtain a more concentrated flavor with delicate teas, use more tea bags, do multiple infusions, or combine the green or white teas with a more robust black tea.

If you use tea bags, adding more of them can help increase the amount of flavor compounds in the brewed tea, creating a more concentrated green or white tea flavor. Avoid steeping the teas for too long; steeping teas longer than the recommended time results in the extraction of more bitter compounds. This over-extraction will create a more bitter tea base. The same caution equally applies to loose leaf teas.

If you use loose leaf teas, multiple infusions will help concentrate the flavor without the risk of over-extraction. A proper method for multiple infusion involves steeping a large amount of tea leaves for 20 – 45 seconds in just enough hot water to cover the leaves. The brewed tea is removed, and another small amount of hot water is added to the leaves and steeped for another short amount of time. This can be repeated 3 – 15 times, depending on the type of tea. This method uses twice the amount of tea leaves with half the amount of hot water [1], essentially concentrating the flavor compounds that diffuse out of the tea leaves. Multiple infusions may not be as effective with tea bags; the tea fannings used for tea bags have small surface areas, and so most, if not all, of the flavor compounds will have quickly diffused into the water in the first steeping.

Sugar can be added to the boiling water before or after steeping the tea, as long as the sugar source completely dissolves. Typically, 1 cup of sugar is added for every 4 cups of boiled water.

2. First fermentation.

Once the tea is finished steeping and the sugar is dissolved, remove the tea bags or strain out the leaves – this is the completed tea base. Tossing the SCOBY (Symbiotic Culture of Bacteria and Yeast) into this freshly-completed tea base willy-nilly will negatively affect the fermentation process, as the microbes within SCOBY thrive best at specific temperatures and pH levels. To ensure a successful fermentation, the tea base has to be adjusted for temperature and pH create a suitable environment for the SCOBY.

  1. Optimum temperature. Recall that SCOBY is alive; wait for the tea base to cool down to at least below 90°F (32°C) before adding SCOBY. A hot tea base would destroy the SCOBY microorganisms, resulting in a complete lack of fermentation. Conversely, do not add SCOBY to a tea base that has been refrigerated to below room temperature, as this would encourage the microbes to go into a dormant state, leading to a very sluggish fermentation process. The optimal temperature to add the SCOBY is between 77°F (25°C) and 90°F (32°C); , as this is the range which SCOBY microorganisms such as Acetobacter and yeast grow best [2,3].
  2. Optimum pH. SCOBY bacteria are acidophiles, meaning that these bacteria thrive in acidic environments. Excluding herbal teas, the teas used for kombucha generally have low pH ranging from 2.9 to 6.3 [4,5]. While this is considered acidic, the pH of the tea base may not be at the optimal range for the Lactobacillus and Acetobacter that inhabit SCOBY, which thrive around pH 5.0 – 6.3 [6,7]. To remedy this, a starter liquid is added to the tea base, which is the liquid that the SCOBY was stored in. Since the starter liquid houses both Lactobacillus and Acetobacter, which produce acid by oxidizing sugar to lactic acid and ethanol to acetic acid, the starter contains a mixture of lactic and acetic acid at a buffered pH that is ideal for the SCOBY. In general, 1 cup of starter liquid is used for every 2 cups of tea base. If there is not enough starter liquid, then plain, store-bought kombucha can be used in lieu of the starter.

SCOBY is added to the tea base in a wide-mouthed container, often a glass jar, to allow for gas exchange and left to ferment for 7 to 10 days at room temperature. During this first fermentation, oxygen has to be abundantly available for Acetobacter, which requires oxygen to grow (it is an obligate anaerobe) [7]. However, leaving the container uncovered puts the kombucha at risk for contamination by fruit flies. Covering the jar with a tightly-woven cloth or paper towel and an elastic band can keep out fruit flies while permitting oxygen availability for the fermenting kombucha. The longer the fermentation period, the more vinegary the flavor and the lower the sugar content.

Kombucha undergoing the first fermentation. Photo credit: Amy Selleck (amyselleck/Flickr)

Kombucha undergoing the first fermentation. Photo credit: Amy Selleck (amyselleck/Flickr)

3. Remove the SCOBY.

To end the first fermenation, simply remove the SCOBY from the kombucha. From here, there are two options: reuse the SCOBY for another batch of kombucha or store it for later brewing.

Reuse: Make another tea base. For the starter liquid, it would be easiest to use the kombucha that the SCOBY was previously removed from.

Store: Store the SCOBY in a tea base/starter liquid mixture. This can be kept at room temperature for up to three weeks, depending on the volume of the storage mixture, before the microbes exhaust the nutrients. For longer storage, place the SCOBY mixture in the refrigerator. SCOBY become dormant in cold temperatures, but this does not mean the microbes cease activity altogether. Rather, in dormancy, cell division halts and the microbes’ metabolism slows significantly [9]. In storage, the SCOBY will continue to ferment its storage mixture, albeit at a slower rate than if left at room temperature. To maintain SCOBY viability, replenish the storage mixture every 4 – 6 weeks by removing 50 – 80% of the liquid and replacing that with new sweetened tea [8]. The main idea is to provide continuing fuel for the microorganisms. It is also possible to simply add ¼ cup sugar per quart of storage mixture every 4 – 6 weeks [8], but keep in mind that the dormant microbes are still carrying out cellular functions which require nutrients and water. The stored SCOBY will reduce the volume of its storage mixture, and so additional tea is required to prevent the storage mixture from drying up.

4. Second fermentation.

Pour the kombucha into bottles and cap them, leaving the bottles out at room temperature. If a flavored kombucha is desired, this is the step to add flavoring ingredients. Although SCOBY was removed at the end of the first fermentation, not all the microorganisms were attached to the cellulose matrix, especially if the microbes were newly-cloned during that previous fermentation period. There will still be kombucha microbes present to perform a second fermentation.

As this second fermentation occurs in a closed system, CO2 produced from the yeast cannot escape the kombucha as it did during the first fermentation. As a result, the kombucha becomes carbonated during this step. Further, the kombucha microbes will continue to metabolize any remaining sugar to produce lactic acid, acetic acid, ethanol, and CO2, so the kombucha will become less sweet but tangier.

After 1 to 3 days, depending on how quickly carbonation occurs, store the kombucha in the fridge. This stops fermentation and carbonation because the significantly decreased temperature causes the microbes to go into a dormant state. And voilá! You have your first batch of kombucha!

Photo credit: thedabblist (64636759@N07/Flickr)

Photo credit: thedabblist (64636759@N07/Flickr)

While making kombucha is a lengthy process that can take up to two weeks to complete one batch, and perfecting the recipe to your own taste will involve making many batches, there is perhaps nothing more satisfying than a successful and delicious kitchen experiment.

The process described in this post was based off of kombucha recipes from The Kitchn and Food52.

References cited

  1. Thoughts on Re-steeping. Teatrekker’s Blog. 22 Sept, 2013.
  2. Science of Bread: Yeast is Fussy about Temperature. Exploratorium.
  3. McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Simon & Schuster, 1997.
  4. pH Values of Common Drinks. Robert B. Shelton, DDS MAGD.
  5. Singh, S., Jindal, R. Evaluating the buffering capacity of various soft drinks, fruit juices and tea. Journal of Conservative Dentistry, 2013; 13(3): 129-131.
  6. Rault, A. Bouix, M., Béal, C. Fermentation pH Influences the Physiological-State Dynamics of Lactobacillus bulgaricus CFL1 during pH-Controlled Culture. Applied and Environmental Microbiology, July 2009; 75(13): 4374-4381.
  7. Hwang, J. W., Yang, Y. K., Hwang, J. K., Pyun, Y. R., Kim, Y. S. Effects of pH and dissolved oxygen on cellulose production by Acetobacter xylinum BRC5 in agitated culture, 1999; 88(2): 183-188.
  8. Take a Break from Making Kombucha Tea. Cultures for Health.
  9. Lahtinen, S. J., Ouwehand, A. C., Reinikainen, J. P., Korpela, J. M., Sandholm, J., Salminen, S. J. Intrinsic Properties of So-Called Dormant Probiotic Bacteria, Determined by Flow Cytometric Viability Assays. Applied and Environmental Microbiology, July 2006; 72(7): 5132-5134.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Kombucha Brewing: The Ingredients

Photo credit: thedabblist (64636759@N07/Flickr)

Kombucha with SCOBY. Photo credit: thedabblist (64636759@N07/Flickr)

Craving some kombucha without the grocery store prices? Why not try brewing your own kombucha? As a fermented tea drink that is brightly effervescent, deliciously tangy, and slightly sweet, having some kombucha on hand could add a little spring to these cold seasons. On top of that, the brewing and fermentation involved in kombucha-making requires a little scientific know-how and quite a bit of trial and error to perfect the flavor to your liking. Think of it as having a science experiment in your kitchen!

At first glance, making kombucha appears fairly simple, as there are only four basic ingredients that go into it: water, tea, sugar, and a “Symbiotic Colony of Bacteria and Yeast,” SCOBY. If a flavored kombucha is desired, specific flavor ingredients can be added too. A cursory investigation into each ingredient, however, may bring up some questions. What type of tea makes the best-tasting kombucha? What is SCOBY and where can you source it? Is it possible to brew a sugar-free kombucha? Here is your scientific guide to making kombucha. We provide some scientific information regarding each component to help make an informed decision in choosing the ingredients that would create the kombucha that best aligns with your preferences.

SCOBY

What is it?

SCOBY is the most important component of kombucha, since it is the only thing standing between ordinary, sweetened tea and kombucha. Other fermented foods which utilize a similar symbiotic culture include kefir, ginger beer, vinegar, and sourdough. SCOBY is a grayish-white or beige, squishy mass floating within the brewed culture, and it is responsible for the distinct vinegar-like flavor, trivial alcohol content, and characteristic carbonation of kombucha. However, to call this leathery, stringy mat a symbiotic colony of microbes is a scientific misnomer. Biologically, a colony implies a coexisting group of individuals within the same species; a microbial colony is a cluster of microorganisms which have descended from a single cell, a common ancestor. SCOBY, on the other hand, is a symbiosis of multiple bacterial and yeast species cohabiting a cellulose matrix [1]. It may be more accurate to describe SCOBY as a biofilm, a colony of several microbial species attached to one another on a surface.

SCOBY

A symbiotic culture of bacteria and yeasts. Photo credit: Robert Anthony Provost (twon/Flickr)

As the name implies, SCOBY is alive. A study on the microbial populations existing in SCOBY reveals that the bacterial genus Gluconacetobacter is the most abundant [1]. Gluconacetobacter is responsible for the biosynthesis of the cellulose matrix that the SCOBY microbial population resides within. In other words, this genus of bacteria enables easy handling by creating the solid, stringy, floating mass that SCOBY is visually famous for. The next most abundant SCOBY bacteria belong to the genera Acetobacter and Lactobacillus [1], both of which give kombucha its acidic, vinegary taste by oxidizing ethanol to acetic acid and sugar to lactic acid, respectively. The yeast population of SCOBY primarily consists of the genus Zygosaccharomyces [1], which is notable for its high sugar, high alcohol, and high acid tolerance [2]. Yeasts in SCOBY generate CO2 and thus provide carbonation; they also produce alcohol, some of which is metabolized by Acetobacter into acetic acid. It is worth noting that the microbial composition of SCOBY may vary over time [1], possibly due to rapid growth, contamination, and/or random mutations. This compositional change may lead to flavor differences among different batches that have used the same SCOBY.

Where do I get it?

Home-brewing stores and online marketplaces are the more common places to buy SCOBY. For the more ambitious, there is also the option to culture SCOBY at home. Given that it is a collection of living organisms, you need to start with some pre-existing collection of kombucha microbes.

To make SCOBY at home, a modest amount of store-bought or homemade, unflavored and unpasteurized kombucha is required. Kombucha often contains a small amount of SCOBY left behind from the brewing process. To begin, place about 1 cup of kombucha with 7 cups sweet tea in a covered container and store for 1 to 4 weeks. In storage, the SCOBY microbes multiply and aggregate, with Gluconacetobacter synthesizing the cellulose that enables the microorganisms to grow together in that signature rubbery mass. For more detailed instructions, check out The Kitchn’s recipe for home-grown SCOBY.

Teas

Which tea?

Kombucha would not be kombucha without tea, but with so many varieties and forms to choose from, it’s easy to get lost. In general, teas are categorized by how the tea leaves (from the plant, Camellia sinensis) were processed, which affects the flavor, caffeine content, and color of the brewed liquid. Varieties among the basic tea categories arise from the geography of C. sinensis, growing conditions, time of harvest, and production processing, giving rise to notable flavor differences. The type of tea chosen will influence the prominent flavor profile of the finished kombucha. For the adventurous, different teas can be mixed together to create a unique kombucha flavor base.

Left to right: green tea, yellow tea, oolong tea, and black tea. Photo credit: Haneburger (Wikimedia Commons)

Left to right: green tea, yellow tea, oolong tea, and black tea. Photo credit: Haneburger (Wikimedia Commons)

  • Black: The most common choice for brewing kombucha, black teas undergo full enzymatic oxidation during production, which gives the drink a dark brown color [3]. Furthermore, complete oxidation of the tea leaves gives black teas a deep malt, caramel, or toasty flavor. This rich tea flavor enables a quick brew without flavor loss during kombucha fermentation.
  • Oolong: Literally translating to “black dragon tea”, oolong teas are partially oxidized, ranging from 8-85% oxidation depending on the tea producer. Oolong flavor profiles fall between the robustness of black teas and the delicacy of green teas, with tones ranging from smoky and buttery to floral and fruity, depending on the amount of oxidation the tea leaves were processed.
  • Green: During production, the oxidation process is stopped early; the tea leaves undergo minimal oxidation, giving green tea a more grassy, floral flavor when compared to other types of teas [3]. Due to their light and subtle flavors, green teas may have to be steeped many times for full flavor, and kombucha with a green tea base may have to be brewed longer.
  • White: Unlike the other teas, white teas are made using only the buds of the C. sinensis plant. Additionally, some white tea varieties use buds that have been steamed or baked, which inactivates enzymatic oxidation. The minimal or absence of oxidation gives white teas a very delicate and subtle grassy flavor, and so this tea may have to be steeped multiple times and a kombucha with a white tea base may have to be brewed for a long time.
  • Pu-erh: Pu-erh stands apart from other teas that use sinensis leaves by an additional fermentation step after the leaves are dried. Fermenting the tea leaves gives pu-erh teas a complex, sweet, earthy flavor profile that the other teas do not have [3].
  • Herbal: Unlike the above four categories, herbal teas rely on steeping plant parts that do not come from sinensis. Herbal teas are strongly advised against for kombucha brewing, as the plants that are used often contain volatile oils that have anti-microbial and/or anti-fungal activity. Some common anti-microbial volatile oils found in herbal teas include lavender oil (from lavender teas), peppermint oil (peppermint teas), and eugenol oil (chai teas) [4], all of which can destroy the bacteria and yeast in SCOBY. A damaged SCOBY will not be able to ferment or carbonate the kombucha batch.

Loose leaf or tea bags?

Tea bags are cheaper and easier to find at the grocery store, but tea bags typically contain fannings or tea dust, which are broken remnants of tea leaves. These remnants were either purposefully crushed for packaging into tea bags or are the leftover fragments after the loose leaf teas are packaged. In contrast, loose leaf teas cost more than their tea bag counterparts and are primarily found in tea specialty stores, but the leaves are much bigger than the fannings found in tea bags. The primary difference between loose leaf and tea bags are the size of the tea leaves, which will affect taste and brew time. Tea leaf sizes do not always correlate to the quality of the tea [5].

Where tea brewing is concerned, fannings have a much greater surface-area-to-volume ratio due to the small particle size, and so will brew much quicker than loose leaf teas. Furthermore, crushed tea leaves may increase the strength of the brewed tea [5]. However, loose leaf teas generally offer more complex, nuanced flavor profiles which tea bags lack. The form of tea to use for brewing kombucha overall depends on personal taste preferences.

Sugar

Which sugar?

At first glance, white sugar seems like the only option, given its ubiquity. For those wishing to experiment a little further, there is no reason to try other sugar sources, since the sugar-metabolizing microbes in SCOBY are not sucrose-specific. There are a couple of notes to consider when choosing the type of sugar:

Brown sugar is sucrose sugar that contains molasses, which may add a molasses flavor to the kombucha.

Raw sugar tend to have bigger crystals, since it is less refined. Bigger sucrose particles may affect its ability to completely dissolve in the kombucha, especially at or below room temperature. If the sugar crystals are not completely dissolved, there may be less sugar in solution available for the bacteria and yeast to metabolize. This could perhaps lead to a more yeasty, rather than fizzy kombucha.

Honey is a mixture of glucose and fructose, with its golden color deriving from non-sugar components such as pollen. Other microorganisms may also be found in honey [6], so using honey for brewing kombucha runs the risk of microbial contamination which may affect SCOBY efficacy.

Sugars extracted from plants or trees other than beets and sugar canes are fair game for brewing kombucha. A few examples include maple syrup, coconut sugar, and palm sugar. Agave nectar, despite health claims, contains a higher fructose content by weight than high fructose corn syrup [7].

Sugar substitutes, such as stevia, xylitol, and glycerol, are sugar alcohols. SCOBY is unable to metabolize sugar alcohols, and so adding artificial sweeteners would not be effective at all in brewing kombucha.

How much sugar?

In kombucha, sugar is used as a food source for the SCOBY, not as a sweetener as in many other recipes. The end product has far less sugar than was originally added to the first fermentation period, as the SCOBY has metabolized most of it to create the vinegary flavor and carbonation. Therefore, adding sugar is necessary for successful fermentation.

Too little sugar, and the SCOBY does not have the necessary fuel to undergo prolonged fermentation, leading to an unsweet, not very acidic, and possibly flat kombucha. Too much sugar may cause the yeast to over-proliferate, outnumbering the other SCOBY microbes. This both decreases the efficacy of the SCOBY and decreases the flavor and carbonation of the resulting kombucha. The exact amount of sugar varies among recipes, and can be experimented with to suit personal preferences.

Flavorings

For a more unique kombucha, flavors are often added near the end of the kombucha brewing process, after the batch has undergone its initial fermentation period. Just like every other component that goes into kombucha, the choices for flavoring are abundant.

Herbs and spices: Since herbs and spices tend to have strong flavors, adding a little bit can go a long way. Keep the amount to a minimum, as some herbs and spices may contain antimicrobial activity, and adding too much may harm the microbes on SCOBY, making the second fermentation period unlikely to occur successfully.

Fruits: Whether fresh fruit or fruit juice is used, be sure to keep an eye on the batch after adding the fruits. Fruits and fruit juices introduce an extra sugar source for the SCOBY during the second fermentation period; the yeast cultures in the SCOBY go into “overdrive” with this added amount of sugar. While this may lead to a fizzier kombucha, the increased carbonation will create a pressure-build up within the container. Opening the container may risk a small kombucha explosion or the container may burst open from the pressure built up.

Kombucha flavored with raspberries. Photo credit: Lukas Chin (Wikimedia Commons)

Kombucha flavored with raspberries. Photo credit: Lukas Chin (Wikimedia Commons)

Extracts and infused waters: Like herbal teas, be sure that the extracts are oil-free as to avoid volatiles that contain anti-microbial activity. A few examples of water-based extracts would be lemon extract (not lemon oil), almond extract, and vanilla. Infused waters include rose water and orange blossom water.

With a little bit of background knowledge, kombucha brewing could become your favorite science project. Explore the possibilities!

References cited

  1. Marsh, A. J., O’Sullivan, O., Hill, C., Ross, R. P., Cotter, P. D. Sequence-based analysis of the bacterial and fungal compositions of multiple kombucha (tea fungus) samples. Food Microbiology, April 2014; 38:171-178.
  2. C. Fugelsang, “Zygosaccharomyces, A Spoilage Yeast Isolated from Grape Juice.”
  3. Types of Tea. TeaSource. 2013.
  4. Thosar, N., Basak, S., Bahadure, R. N., Rajurkar, M. Antimicrobial efficacy of five essential oils against oral pathogens: An in vitro European Journal of Dentistry, Sept 2013; 7:71-77.
  5. Does the size of your tea leaf matter? Octavia Tea. 18 November, 2011.
  6. Olaitan, P. B., Adeleke, O. E., Ola, I. O. Honey: a reservoir for microorganisms and an inhibitory agent for microbes. African Health Sciences, Sept 2007; 7(3):159-165.
  7. Bowden, Jonny. Debunking the Blue Agave Myth. Huffington Post. 17 April, 2010.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Vinaigrette

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Homemade vinaigrettes are about as easy as they look: mix oil, vinegar, and spices; shake before pouring. For those who want vinaigrettes without the inelegant step of shaking before serving, the solution is simple; add an emulsifier.

Understanding the role of an emulsifier first requires some familiarity with the primary components in vinaigrette, vinegar and oil. Vinegar is composed of acetic acid and water, which are polar compounds. In a polar molecule, one or a group of atoms have a stronger pull on the electrons in the molecule. Due to this uneven share of electrons between the atoms, weak charges form on opposite ends of the molecule [Figure 1a]. The weakly positive and negative charges on the polar molecule are called dipoles. Oil, on the other hand, is a type of lipid, which is a nonpolar compound. Since the atoms within the lipid are largely identical, the electrons are evenly distributed across the lipid molecule [Figure 1b]. Therefore, nonpolar molecules do not have such well-developed dipoles.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

In solutions, compounds follow the chemistry fiat, like dissolves like. Polar molecules only interact with other polar molecules. Likewise, nonpolar molecules prefer to be surrounded by other nonpolar molecules. When a polar solution, like vinegar, is vigorously mixed with a nonpolar solution, like oil, the two initially form an emulsion, a mixture of polar and nonpolar compounds. However, this emulsion is unstable and will very quickly form layers in what’s known as phase separation. The solutions separate into layers according to their respective densities due to an aversion to each other. (In this case, because oil has a lower density than vinegar, it happens to be the layer floating on top.)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

To prevent phase separation, an emulsifier can be added to the vinaigrette to stabilize the emulsion. Emulsifiers are amphipathic compounds, meaning the molecule has both a polar and nonpolar section [Figure 2]. Common food emulsifiers include egg yolk, soy lecithin, garlic, and mustard. Egg yolk contains the emulsifying agent lecithin. The vegan version is isolated from soy and is thus known as soy lecithin. Lecithin is a commonly used emulsifier in many other food products, such as chocolates, mayonnaise, and Hollandaise sauce. Amphipathic compounds found in garlic include diallyl sulfide, allyl methyl disulfide, and diallyl trisulfide [1]. Mustard, the condiment, is made from mustard seeds. Emulsifying agents in the condiment, such as the pectin rhamnogalacturonan, originate from the mucilage of mustard seeds, a thick, glutinous layer that surrounds the seed hull [2,3].

Figure 2. a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

So with a helping hand from emulsifiers, homemade vinaigrettes can still be as simple yet elegant as they seem, and best of all, ready to serve whenever.

Greek Salad Vinaigrette (Recipe from Ina Garten’s Barefoot Contessa)

½ cup olive oil
¼ cup red wine vinegar
2 cloves garlic, minced
½ tsp Dijon mustard
½ tsp ground black pepper
1 tsp salt
1 tsp dried oregano

  1. In a bowl, whisk together the vinegar, garlic, mustard, salt, pepper, and oregano until well mixed.
  2. While still whisking, slowly add the olive oil.
  3. When a stable emulsion forms, serve with salad or store in a covered bowl or bottle.

References cited

  1. Kimbaris, A.C., Siatis, N.G., Pappas, C.S., Tarantilis, P.A., Daferera, D.J., Polissiou, M.G. Quantitative analysis of garlic (Allium sativum) oil unsaturated acyclic components using FT-Raman spectroscopy. Food Chemistry, 2006; 94: 287-295.
  2. Cui, W., Eskin, M.N., Biliaderis, C.G., Marat, K. NMR characterization of a 4-O-beta-D-glucuronic acid-containing rhamnogalacturonan from yellow mustard (Sinapis alba L.) mucilage. Carbohydrate Research, 1996; 292(1): 173-183.
  3. Leroux, J., Langendorff, V., Schick, G., Vaishnav, V., Mazoyer, J. Emulsion stabilizing properties of pectin. Food Hydrocolloids, 2003; 17: 455-462.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Homemade Marshmallows

Photo Credit: Heather Katsoulis (hlkljgk/Flickr)

Photo Credit: Heather Katsoulis (hlkljgk/Flickr)

Whether you prefer them toasted over a campfire, bobbing in a cup of hot chocolate, or roasted over a bed of sweet potatoes, marshmallows are an ooey-gooey fluffy treat that just finds a way warm the cockles of your heart.

Marshmallows, like other well-known aerated confections – think mousses, ice cream, meringues –  are essentially made of four basic components: sugar, water, air, and a hydrocolloid.  Hydrocolloids, often called “food gums” are polysaccharides, or typically large-branching proteins, that form thick gels when they interact with water. [1]

Their ability to bind to water molecules makes them hydrophilic (or “water-loving”), and their ability to remain suspended and dispersed evenly in the water (without settling to the bottom) makes the substance a colloid. Thus, food gums are hydrophilic colloids, or hydrocolloids.

Photo Credit:  Daniel Campagna (Chefpedia)

Photo Credit: Daniel Campagna (Chefpedia)

Hydrocolloids are added to many foods we eat – as thickening agents in pie fillings or gravies, gelling agents in puddings and jams, foam stabilizers in beer and meringues, film formers in sausage casings, emulsifiers in salad dressing, and even fat replacers in frostings and muffins.  Common examples of hydrocolloids are starch, xanthan gum, locust bean gum, alginate, pectin, carrageenan, and agar, which all influence the texture and mechanical stability of many foods.  [1][2]

In marshmallows, the hydrocolloid responsible for the chewy, bouncy texture we know and love is gelatin. While gelatin is one of the most popular commercial hydrocolloids, it is definitely not the most glamorous.  Gelatin is made of collagen, which is the structural protein derived from animal skin, connective tissue, and bones. In fact, mainstream gelatin is usually obtained from pigskin, cattle bones, and cattle hide. [3] Gelatin is unique because not only does it function as a foam stabilizer for the marshmallows [4], but when it is mixed with water, gelatin forms a thermally-reversible gel.  These gelatin gels have a melting temperature just below body temperature (< 35°C or 95 °F), so the gel product literally melts in your mouth and releases intense flavor immediately as it dissolves, which is a difficult quality to replicate with other hydrocolloids. [3]  

Gelatin makes marshmallows chewy by forming a tangled 3-D network of polymer chains.  Once gelatin is dissolved in warm water (dubbed the “blooming stage”), it forms a dispersion, which results in a cross-linking of its helix-shaped chains.  The linkages in the gelatin protein network, called “junction zones” trap air in the marshmallow mixture and immobilize the water molecules in the network . The result? The famously spongy structure of marshmallows! [1]  This is why the omission of gelatin from a homemade marshmallow recipe will result in marshmallow crème, since there is no gelatin network to trap the water and air bubbles.

And for the gelatin-averse, worry not! There are indeed many hydrocolloid alternatives to gelatin. However, since gelatin has so many different functions (gelling agent, emulsifier, stabilizer, thickener, etc.), its alternatives are not universal. Rather, substitutes are specific to each specific food application. In our case, some have suggested pectin – a polysaccharide from the cell walls of plants – as the ideal replacement for gelatin in marshmallows [1].

Agar agar is a commonly used vegetarian alternative for jellies.  Photo Credit: I Believe I Can Fry (johnnystiletto/Flickr)

Agar agar is a commonly used vegetarian alternative for jellies.
Photo Credit: I Believe I Can Fry (johnnystiletto/Flickr)

Pectin, carrageenan (a polysaccharide from red seaweeds), or combinations of both can replicate the elastic texture and intense flavor release that gelatin provides for marshmallows. However, since the melting points of both pectin and carrageenan are not the same as the melting point of gelatin – which, as you recall, is slightly below body temperature, marshmallows made with pectin or carrageenan don’t have the quite the same “melt-in-your-mouth” sensation. [1]

* Note: Carrageenan gels are unique in that their melting temperature can be modified, depending on the solution concentration of the carrageenan and the presence of cations, so the melting temperature ranges from 40°C (104°F) and 70°C (158°F).

* Note: Carrageenan gels are unique in that their melting temperature can be modified, depending on the solution concentration of the carrageenan and the presence of cations, so its melting temperature ranges from 40°C (104°F) and 70°C (158°F).

As you can see, none of the gelatin alternatives have the appropriate melting temperatures to replicate gelatin’s melt-in-your-mouth sensation. However, this does prove advantageous in the fact that they can last longer on hot days or in hot, tropical climates and they do not require refrigeration to set.

No matter what you prefer for as a hydrocolloid, pillowy marshmallows can made with the same basic recipe:

Photo Credit: Joy (joyosity/Flickr)

Photo Credit: Joy (joyosity/Flickr)

Ingredients

For the bloom:
3 tablespoons (typically 3 packets) unflavored gelatin powder
1/2 cup cold water

*Vegan Substitution: 2 ½ tablespoons agar agar + ½ cup and 2 tablespoons water
Alternatively, this vegan marshmallow recipe is worth checking out:

For the marshmallows:
3/4 cup water
1 1/2 cups granulated sugar
1 1/4 cup sugar cane syrup or corn syrup
Pinch of salt

For the marshmallow coating:
1 1/2 cups powdered sugar
1/2 cup cornstarch
non-stick cooking spray


Equipment
Bowls and measuring cups
Fork or small whisk
9×13 baking pan or other flat container
4-quart saucepan (slightly larger or smaller is ok)
Pastry brush (optional)
Candy thermometer
Stand mixer with a wire whisk attachment
Stiff spatula or spoon (as opposed to a rubbery, flexible one)
Sharp knife or pizza wheel

Instructions

  1. Prepare pans and equipment: Spray the baking pan with cooking spray. Use a paper towel to wipe the pan and make sure there’s a thin film on every surface, corner, and side. Set it near your stand mixer, along with the kitchen towel and spatula. Fit the stand mixer with the whisk attachment.
  2. Bloom the gelatin/agar: Measure the gelatin or agar into the bowl of the stand mixer. Combine 1/2 cup cold water in a measuring cup and pour this over the gelatin or agar while whisking gently with a fork. Continue stirring until the gelatin or agar has dissolved or reached the consistency of apple sauce and there are no more large lumps. Set the bowl back in your standing mixer. (Alternatively, you can bloom the gelatin or agar in a small cup and transfer it to the stand mixer.)
    * NOTE: You can add about 1 tablespoon of powdered flavorings to your hydrocolloid while it is blooming in the water.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  3. Combine the ingredients for the syrup: Pour 3/4 cup water into the 4-quart saucepan. Pour the sugar, corn syrup, and salt on top. Do not stir.
  4. Bring the sugar syrup to a boil: Place the pan over medium-high heat and bring it to a full, rapid boil — all of the liquid should be boiling. As it is coming to a bowl, occasionally dip a pastry brush in water and brush down the sides of the pot. This prevents sugar crystals from falling into the liquid, which can cause the syrup to crystallize. If you don’t have a pastry brush, cover the pan for 2 minutes once the mixture is at a boil so the steam can wash the sides.
    Do not stir the sugar once it has come to a boil or it may crystallize!
  5. Boil the syrup to 247°F to 250°F: Clip a candy thermometer to the side of the sauce pan and continue boiling until the sugar mixture reaches 247°F to 250°F. Take the pan off the heat and remove the thermometer.
  6. Whisk the hot syrup into the gelatin / agar: Turn on your mixer to medium speed. Carefully pour the hot sugar syrup down the side of the bowl into the gelatin or agar. The mixture may foam up — just go slowly and carefully.
  7. Increase speed and continue beating: When all the syrup has been added, cover the bowl with a clean kitchen towel and increase the speed to high (the cloth protects from splatters — the cloth can be removed after the marshmallows have started to thicken).

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  8. Beat marshmallows until thick and glossy: Whip for about 10 minutes. At first, the liquid will be very clear and frothy. Around 3 minutes, the liquid will start looking opaque, white, and creamy, and the bowl will be very warm to the touch. Around 5 minutes, the marshmallow will start to increase in volume. You’ll see thin, sticky strands between the whisk and the side of the bowl; these strands will start to thicken into ropes over the next 5 minutes. The marshmallow may not change visually in the last few minutes, but continue beating for the full 10 minutes. When you finish beating and stop the mixer, it will resemble soft-serve vanilla ice cream.
    * NOTE: Add 1- 2 tablespoons of liquid flavorings during the last couple minutes of the beating process. (See Ideas Section below.)
  9. Immediately transfer to the baking pan: With the mixer running on medium, slowly lift (or lower, depending on your model) the whisk out of the bowl so it spins off as much marshmallow as possible. Using your stiff spatula, scrape the as much of the thick and sticky marshmallow mixture into the pan as you can.
    * NOTE: If you want mini marshmallows, after mixing, immediately put the mixture in a piping bag and pipe out your mini marshmallows in the size and shape of your choice.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  10. Let the marshmallows set for 6 to 24 hours: Spray your hands lightly with cooking oil and smooth the top of the marshmallow to make it as even as possible. Let the mixture sit uncovered and at room temperature for 6 to 24 hours to set.
  11. Prepare the marshmallow coating: Combine the powdered sugar and cornstarch in a bowl.
  12. Remove the marshmallows from the pan: Sprinkle the top of the cured marshmallows with some of the powdered sugar mix and smooth it with your hand. Flip the block of marshmallows out onto your work surface. Use a spatula to pry them out of the pan if necessary. Sprinkle more powdered sugar mixture over the top of the marshmallow block.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  13. Cut the marshmallows: Using a sharp knife or pizza wheel, cut the marshmallows into squares. It helps to dip your knife in water every few cuts. (You can also cut the marshmallows with cookie cutters.)
  14. Coat each square with powdered sugar mix: Toss each square in the powdered sugar mix so all the sides are evenly coated.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  15. Store the marshmallows: Marshmallows will keep in an airtight container at room temperature for several weeks. Leftover marshmallow coating can be stored in a sealed container indefinitely.

Ideas:

  • Add Flavorings: You can add about a tablespoon of either powdered or liquid flavorings/food colorings to the marshmallows at Step 2 or Step 8, respectively, in the recipe.
  • Sweet Marshmallows
    – classic: vanilla extract, almond extract, cocoa powder
    – floral: rose water, orange blossom water
    – spiced: cinnamon, pumpkin spice, cardamom, nutmeg, chai tea, peppermint
    – fruity: passion fruit, strawberry, mango, lemon juices
  • Savory Marshmallows
    –  A great base for savory marshmallows: PopSci:Sechuan Peppercorn Marshmallow
    – garlic salt and pepper
    – pesto (I’m imagining a pillowy caramelized pesto-marshmallow roasted on top of a pizza!)
    – hot sauce
  • Add citric acid or cream of tartar to stabilize the inverted sugars in your recipe and prevent them from crystallizing, essentially ensuring that your marshmallows remain fluffy and chewy.
  • Add your sugar syrup into whipped egg whites to incorporate extra air volume and structure for spongier, pillowy marshmallows.
  • DIY Lucky Charms: You can make your own dehydrated marshmallows, similar to the ones found in breakfast cereals (but without all the suspicious additives) by evaporating the water from the sugar solution in your homemade marshmallows.  Various methods are described here.


Recipe adapted from

References Cited

    1. Saha, D., Bhattacharya, S. Hydrocolloids as thickening and gelling agents in food: a critical review. Journal of Food Science and Technology. December 2010; 47(6): 587-597.
    2. Gum“. Food @ OSU.
    3. Karim, A. A., Bhat, R. Gelatin alternatives for the food inudustry: recent developments, challenges and prospects. Trends in Food Science & Technology. December 2008; 19(12): 644-656.
    4. Gelatin. Gelatin Food Science. 14 Dec. 1998.

Eunice LiuAbout the author: Eunice Liu is studying Neuroscience and Linguistics at UCLA. She attributes her love of food science to an obsession with watching bread rise in the oven.

Read more by Eunice Liu


Bar Stools and Molecules: Buttery Nipple Science

[Photo Credit: Vince C Reyes]

[Photo Credit: Vince C Reyes]

You may think a buttery nipple is just a fun shot to buy a friend on his or her birthday, but it’s more complex than that. It’s got layers… specifically two. For those not familiar with the bar classic, the buttery nipple is composed of a layer of Irish cream sitting on top of butterscotch schnapps.

Buttery Nipple Shot Recipe

½ oz. Irish cream
1 oz. Butterscotch schnapps

  1. Pour 1 oz. of Butterscotch schnapps into a chilled shot glass.
  2. Carefully pour ½ oz. of Irish cream onto the back of a downturned spoon so it rolls from the spoon and floats on the surface of the schnapps.
  3. Enjoy!

This and other layered shots like the American flag, the B-52, and the Alien Brain Hemorrhage, take advantage of the slight differences in density among spirits. As density, a substance’s mass per unit volume (Density = mass / volume), dictates the layering in these drinks; the most dense liquid is placed at the bottom followed by progressively less dense liquids. In the case of the buttery nipple, the less dense Irish cream floats on the more dense butterscotch schnapps. If you were to reverse the order with the butterscotch schnapps poured on the Irish cream, the layers would not form. The more dense butterscotch schnapps would sink to the bottom of the glass and result in a mixture of the two spirits.

For the home bartender looking to make new layered drinks, the absolute density of a spirit is not always easy to measure. However, a different quantity, specific gravity, is often available online1. Specific gravity is the ratio of the density of substance to water (specific gravity = density of a substance / density of water). Water has a specific gravity of 1.0. More dense liquids have specific gravities greater than 1.0 and less dense liquids have specific gravities less than 1.0. In the case of the buttery nipple shot, butterscotch schnapps (Dekyper’s ButterShots) has a specific gravity of 1.12 while Irish cream (Bailey’s) has a specific gravity of 1.06.1 The specific gravity is often available online for alcoholic beverages because it is important in the fermentation and distillation process, and different beers, wines, and spirits have characteristic specific gravities.

If the specific gravity of an alcoholic beverage cannot be found, some recommend using proof or alcohol by volume (ABV) to layer drinks. Both are mandated on all alcoholic beverages sold and therefore easy to find. In general, proof is the amount of alcohol in a beverage. Specifically in the US, proof is defined as twice the percentage of the alcohol by volume. The alcohol in any beverage you drink is ethyl alcohol, also called ethanol (C2H6O).

Figure 1: Molecular Formula of Ethanol [Image Credit: Vince C Reyes]

Figure 1: Molecular Formula of Ethanol [Image Credit: Vince C Reyes]

At room temperature (77°F or 25°C), ethanol has an absolute density of 789.00 kg/m3 and a specific gravity of 0.7872. As many alcoholic spirits are primarily a mixture of ethanol and water, which has an absolute density of 999.97 kg/m3 and specific gravity 1.0, greater alcohol content can often correspond to a smaller density. For example in the case of the buttery nipple, Irish cream (Baily’s) is 17% ABV, while Butterscotch schnapps is 14.8% ABV. Therefore, the higher alcohol content and corresponding lower density of the Baily’s Irish cream allows it to sit on top of butterscotch schnapps. This shortcut, however, is not always correct as many spirits have ingredients other than water and ethanol. Many spirits contain cream, sugars, or other flavoring agents, which can change their densities, making alcohol content an imperfect proxy for density. For example, Smirnoff’s flavored vodkas all have 35% ABV, but have varying specific gravities: citrus vodka has a specific gravity of 0.96, while the more dense watermelon vodka has a specific gravity of 0.981.

Figure 2: Layering in a Buttery Nipple.  *ABV is not always an indicator of density. [Image Credit: Vince C Reyes]

Figure 2: Layering in a Buttery Nipple.
*ABV is not always an indicator of density. [Image Credit: Vince C Reyes]

Lastly although other factors such as altitude affect density, temperature is the other most relevant factor for an aspiring bartender. Liquids are denser when cold. Temperature is an indicator of the speed of molecules within a substance. At low temperatures, liquids have slower moving molecules that pack closer together resulting in greater mass per volume. In contrast, at higher temperatures, molecules in liquids move around more quickly and take up less space resulting in a reduced density. For example, water near room temperature (70°F [21°C]) is less dense (0.998 g/cm3), than water near freezing (1.000 g/cm3 at 39.2 °F [4.0 °C])3. This is why using chilled spirits, glass wear, and spoons when making a layered shot can ensure that spirits remain at their densest and form layers.

Ultimately, a great layered shot is one that is not only effectively layered, but also delicious. If you don’t enjoy the buttery nipple, you now have the scientific knowledge to experiment with your own concoctions!

Learn more

  1. Specific Gravity of Different Spirits from GoodCocktails.com
  2. Specific Gravity of Other Liquids from Engineering Tool Box
  3. The Density of Water at Different Temperatures from the US Geological Survey

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

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Beer Crust Apple Pie

The Science of Pie – June 1, 2014
Best Scientific Pie
Christina Cheung, Tori Schmitt, and Elliot Cheung (Team Pretty Intense Pie Enthusiasts)

Adding alcohol to a pie crust is a fairly mainstream way of obtaining a nice flaky shelter for a delicious filling within. Vodka is the go-to spirit for crusts, but other beverages have found their way into the realm of apple pies too. One team at the 2014 Scientific Bake-Off, team P.I.E. (Pretty Intense Pie Enthusiasts), was intrigued by the plethora of alcoholic options available to them for pie crusts, and chose to use their scientific prowess to determine the best choice. Two variables guided their experiment: how do carbonation and alcohol concentration affect the flakiness of a pie crust?

Christina Chung presenting team P.I.E's experiment to the judges (Photo Credits: Patrick Tran)

Christina Chung presenting team P.I.E’s experiment to the judges (Photo Credits: Patrick Tran)

Team P.I.E. began by making six experimental crust doughs, each containing either water, beer, stale beer, diluted vodka, regular vodka, and Perrier. To measure flakiness, a quality difficult to quantify, they compared the average height for each baked pie dough to indicate how much the dough has risen during baking. To account for bubbles, height measurements were taken at the center and edges of the crust.

Elliot Cheung hard at work preparing pie (Photo Credit: Patrick Tran)

Elliot Cheung hard at work preparing pie (Photo Credit: Patrick Tran)

These pie researchers calculated the elastic modulus of each crust to further quantify flakiness. Elastic modulus of a substance is the ratio of the stress applied to the resulting strain. This ratio can be thought of as a measure of  stiffness, or in our case, flakiness, as the flakiest crust will break the most easily. 

Pie crusts that utilized both forms of beer had a higher average elastic moduli than crusts with other binding agents.

Pie crusts that utilized both forms of beer had a higher average elastic moduli than crusts with other binding agents.

Pie crusts with Perrier as a binding agent yielded the greatest average heights

Pie crusts with Perrier as a binding agent yielded the greatest average heights

They administered force to their crusts by using a pen to mimic the conditions of fork prongs stabbing a pie crust. Measured values of water balanced atop the pen acted as a weight to provide precise values of force.

Through this extensive research, P.I.E. presented data that showed that a pie crust made with Perrier sparkling water created a significantly thicker crust than one made with any of the other experimental liquids. All the other crusts surprisingly rose to very similar heights.  Since P.I.E had observed similar bubble size and bubble concentration in Perrier and beer, they expected that the regular beer crust would yield similar data to the Perrier crust. However, the significant difference between the measured values  of Perrier and beer imply a confounding factor in the experimental comparison. They speculate that Perrier’s high mineral content could alter the vaporization temperature of the liquid, and thus affect the creation of air bubbles and the dough’s infrastructure.

The dedication to detail and the scientific method paid off for these three scientists, as the panel of esteemed judges awarded them the title of “Best Scientific Pie”. As this was a scientific bake off, that is a pretty high honor to hold. Congratulations to the Pretty Intense Pie Enthusiasts, and we thank you for your deliciously scientific dessert!

Christina Cheung, Tori Schmitt, and Elliot Cheung accept their awards for Best Scientific Pie

Christina Cheung, Tori Schmitt, and Elliot Cheung accept their awards for Best Scientific Pie (Photo Credits: Patrick Tran)

Recipe
Beer Crust Apple Pie

(Makes two full pies)

For crust:

  • 5 cups flour
  • 2 TB sugar
  • 2 t salt
  • 4 sticks chilled butter
  • 1/2 to 1 cup cold beer (we used Blue Moon, but any pale ale works here)

Combine flour, sugar, and salt in a large bowl. (if making full recipe will require a very large bowl) Cut chilled butter into cubes and cut into flour mixture with a fork or pastry cutter.  The flakes can vary in texture but absolutely no butter cubes should remain intact. The mixture will resemble corse sand.  Measure out beer starting at 1/2 cup.  Pour in and incorporate into dough. If dough is still dry, incorporate more beer in until the dough is just moist enough to stick together.  Wrap dough in saran and refrigerate for at least 30 minutes, up to overnight.

For Filling and Assembly:

  • 8 large apples (we used a mixture of granny smith and pink lady)
  • 1 cup sugar
  • 6 tablespoons flour
  • salt and cinnamon to taste
  • Lemon zest (roughly 2 TB)
  • one bottle of beer or hard apple cider
  • egg white to brush the top with
  • 1/2-3/4 cup of shredded gruyere cheese

To prep the filling, core and peel all your apples and soak them in enough beer and/or hard cider to cover for 1-2 hours or until the apples are infused to taste. Pour out liquid and reserve for reduction sauce later. Be sure to remove all the liquid from the bowl and allow the apples to dry for roughly 30-45 minutes.  The apples will look significantly less “wet” after the drying period.  After the apples are dry, combine them with flour, sugar, lemon zest, cinnamon, and salt.  Depending on the sweetness of your hard cider/beer, you may need to adjust the amount of sugar used.

Assembly:

Pre-heat home oven to 500 degrees. Section pre-chilled pie dough into four equal segments and roll out two of the pie dough segments. Place these over buttered glass pie dishes and fold into place. Split filling evenly and pour into each dish. Dot top of apples if additional butter if desired (roughly 1 TB per pie).  Roll out the remaining pie crust into two top pieces.  Sprinkle each top pie with an equal amount of cheese.  Cheese amount will depend on strength and personal preference for cheese.  Flour pin well and lightly roll/ press cheese gently into the crust (dough will be very flaky).  Lay top crust evenly over pie with cheese side facing up. Crimp edges and brush with egg whites.

To bake the pie. place and oven and lower temp to 425 degrees F.  Bake at this temp for 25 minutes at which point, rotate the pie and lower temp to 375 for an additional 30-35 minutes. This will produce a pie with softer apples.   Alternatively the pie can be baked at 375 for a full hour, however the apples may remain more al dente.  (Pie was baked in the second way for competition)


Elsbeth SitesAbout the author: Elsbeth Sites is pursuing her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

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Crumbalicious Apple Pie

The Science of Pie – June 1, 2014
Best Overall Pie & People’s Choice Pie
Alina Naqvi & Ashley Lipkins-Scott (Team Apple Queens)

This duo of student scientists aimed to create a pie with the crunchiest apple filling by experimenting with four different types of apples: Granny Smith, Red Delicious, Pink Lady, and Fuji. To determine which apples had the greatest resistance to applied forces (and thus remained crunchiest), they measured both the force required to cut through each kind of apple and the “elastic modulus”, which is the amount of deformation caused by a given force.

(A) Team Apple Queens receives the People’s Choice Award at the 2014 Xcience of Pie event. (B) Lipkins-Scott carries the team’s cinnamon crumb pie to the oven. (C) Fuji and Granny Smith apples were used for the Apple Queens’s pie because the team found that these apple varieties had the highest values for elastic modulus. Photos courtesy of Patrick Tran.

To measure the elastic modulus for each apple variety, the team applied a known weight to the apple slice and measured the deformation using a ruler before and after the apples were cooked. (See Panel A & B below). In addition, they wanted to see which apples had the most resistance (and thus, crunch) by measuring the force used to cut through the apples in a “Puncture Force” Test. For this test, the team added increasing volumes of water into a pot balanced over a knife to determine the mass of water required for the knife to cut through the apple slice. (See Panel C below).

After the apples are baked, their lengths (A) and deformations (B) are measured to obtain the elastic modulus. (C) The Puncture Force Test measures the force required to cut through the cooked apples.

Before baking, the Fuji apple had the highest elastic modulus of 170,000 N/m2 and the Pink Lady had the lowest elastic modulus of 130,000 N/m2. After baking, the Granny Smith had the highest elastic modulus of 32,000 N/m2 and the Fuji had the second highest elastic modulus at 28,000 N/m2.

In the Puncture Force Test, the baked Granny Smith apple required the highest puncture force of 18N.

Team Apple Queens found that the cooked Granny Smith apples exhibited the highest elastic modulus and also required the greatest force to cut through. Thus, the Granny Smiths were most resistant to external pressure and remained the crunchiest after baking. Having both the second highest elastic modulus and the second greatest puncture force were the Fuji apples. Based on these results, the team hypothesized that Granny Smith and Fuji apple varieties may contain more of the polysaccharide pectinto fortify their cell walls and make them harder, crunchier apples.

The students of Team Apple Queens stand proudly by their winning pie and poster.

Recipe
Crumbalicious Apple Pie

For the crust:
1 1/3 cup all purpose flour
1⁄2 teaspoon salt
1⁄4 cup (1/2 stick) chilled unsalted butter, cut into 1⁄2-inch cubes
1⁄4 cup frozen solid vegetable shortening, cut into 1⁄2-inch cubes
3 tablespoons (or more) ice water
1⁄2 teaspoon apple cider vinegar

For the filling:
3 Granny Smith apples, peeled, cored, and sliced 1⁄4 inch thick
1 Fuji apple, peeled, cored, and sliced 1⁄4 inch thick
2/3 cup cane sugar
2 tablespoons all purpose flour
2 teaspoons ground cinnamon
2 tablespoons unsalted butter, melted

For the topping:
1 cup all purpose flour
1⁄2 cup cane sugar
1⁄4 cup brown sugar
1 and 1⁄2 teaspoons ground cinnamon
1⁄2 teaspoon salt
6 tablespoons chilled unsalted butter, cut into 1⁄2-inch cubes

Position a rack in the center of the oven and preheat to 375°F.

To prepare the crust:
In a large bowl, mix flour, salt, and sugar. Add butter and shortening; rub in with fingertips until coarse meal forms. We want to incorporate flattened sheets of butter into the flour mixture to get a flaky crust.

In a small bowl, mix three tablespoons of ice water and vinegar. Drizzle the water and vinegar solution over flour mixture. Stir with fork until moist clumps form, adding more water by teaspoonfuls if dough is dry.

Gather dough into ball; flatten into disk. Wrap in plastic and refrigerate for at least 30 minutes. Refrigeration is important for allowing gluten strands to relax (so the dough becomes easier to roll out), and for letting letting liquids incorporate to moisturize the dough.

Roll out dough on lightly floured surface to 12-inch round. (About 1/8th 9-inch-diameter glass pie dish.) Trim overhang to 1/2 inch; turn edge under and crimp decoratively.

Refrigerate while preparing filling and topping.

To prepare the filling:
Mix all ingredients in a large bowl to coat apples.

To prepare the crumble topping:
Blend all ingredients until mixture resembles wet sand.

To assemble the pie:
Toss the filling to redistribute juices and then transfer to crust, mounding in center. Pack topping over and around apples. Bake pie on baking sheet until topping is golden, about 1 hour (cover top with foil if browning happens too quickly). Cool until warm, about 1 hour.

Recipe adapted from Bon Appétit: Cinnamon Crumble Apple Pie


Eunice LiuAbout the author: Eunice Liu is studying Neuroscience and Linguistics at UCLA. She attributes her love of food science to an obsession with watching bread rise in the oven.

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