Science & Food – Page 7 – Science and Food

Ramen and the Perfect Egg

October 7, 2014/in Science & Food/by Grant Alkin

The arrival of autumn comes with the promise of changing leaves and chillier climates, often cueing our urge to prepare warmer meals aimed at combatting the frigid weather. One foolproof method that guarantees victory against the cold is a hot bowl of soup, such as ramen. There are many variations of ramen but one dear to many hearts (and mouths) is tonkotsu ramen. This style of ramen involves the boiling of pork bones for extended periods of time to produce a deliciously fatty and hearty pork broth that has an incredible depth of flavor. The broth alone is what makes the ramen but the accoutrements that dress the soup are just as important. Tonkotsu ramen is often served with slices of marinated, slow-cooked pork loin (chashu), enoki and wood ear mushroom, dried seaweed (nori), and green onions. However, one of my favorite ramen toppings is the soy-marinated soft-boiled egg known as ajitsuke tamago.

Photo credit: Anne Regalado (My Bare Cupboard)

Perfectly prepared ajitsuke tamago has a set outer layer of egg white with a delicate, intact silky egg yolk. However, achieving the ideal soft-boiled egg isn’t a trivial task. The preparation of both hard and soft-boiled eggs culminates in the process known as protein denaturation. Eggs themselves are nothing more than protein reservoirs and their exposure to heat disrupts the chemical and ionic bonds involved in maintaining their secondary and tertiary configurations causing them to unfold into linearized structures [1]. The unfolding of complex proteins into strings of amino acid chains through thermal energy transfer allows for the formation of new bonds between molecules that facilitate the transition of a raw, liquid egg into a cooked, solid egg [1]. Ovotransferrin and ovalbumin and are the most abundant proteins found in egg whites and their denaturation causes them to form tightly associated protein clumps that result in the solidification of the egg whites at 140°F and 180°F, respectively. [2,3]. Furthermore, the egg yolks will also become solid once they reach a sustained temperature of 160°F. Therefore, one must consider the balance of temperature and time to attain the characteristics of a perfectly soft-boiled egg.

Heat causes the phase transition of the egg from a liquid state to a water-insoluble state that’s ready for eating! Photo Credit: SPIE

Timothy Ferriss, author of The 4-Hour Chef [4], conducted an experiment to dispel our egg boiling anxieties. He placed four eggs in a pot of water and brought it to boiling temperature (212°F); after 6 minutes he removed each of them in 2-minute increments. His verdict? The sweet spot to achieve the perfect ajitsuke tamago egg consistency is somewhere between 6-7 minutes (see image below). I’d err between 5-6 minutes, as the salt from the soy-marinated will continue to “cook” the outer egg white layer.

Photo Credit: The 4-Hour Chef

If you enjoy the challenge of making dishes at home, check out this tutorial on how to make your own tonkotsu ramen!

Tonkotsu Ramen Broth

Ingredients

3 pounds pig trotters, split lengthwise or cut crosswise into 1-inch disks (as your butcher to do this for you)
2 pounds chicken backs and carcasses, skin and excess fat removed
2 tablespoons vegetable oil
1 large onion, skin on, roughly chopped
12 garlic cloves
One 3-inch knob ginger, roughly chopped
2 whole leeks, washed and roughly chopped
2 dozen scallions, white parts only (reserve greens and light green parts for garnishing finished soup)
6 ounces whole mushrooms or mushroom scraps
1 pound slab pork fat back

Full recipe at Food Lab.

References cited

Nelson, D; Cox, M (2012). Lehninger Principles of Biochemistry. 4th Ed. New York: W.H. Freeman
Huntington JA; Stein PE (2001). Structure and properties of ovalbumin. Journal of Chromatography B 756 (1-2): 189–198
Wu, J, Acero-Lopez, A (2012). Ovotransferrin: Structure, bioactivities, and preparation. Food Research Int 46: 480-487
Ferriss, T (2012). The 4-Hour Chef. Boston: New Harvest

About the author: Anthony Martin received his Ph.D. in Genetic, Cellular and Molecular Biology at USC and is self-publishing a cookbook of his favorite Filipino dishes.

Read more by Anthony Martin

Ginger

September 30, 2014/in Flavor of the Month/by Grant Alkin

Photo Credit: Jim Lightfoot (112095551@N02/Flickr)

One rhizome, many tastes. Ginger can be charmingly sweet as candied ginger, gingerbread, and ginger ale. Just as easily, this root can be spiritedly pungent, as in gari (sushi ginger) or unsweetened ginger tea. From sugary snacks to savory dishes, ginger shares similar flavor versatility as cardamom, which should come as no surprise; the two spices are practically cousins. All ginger plants are of the genus Zingiber, which belongs to the same family as cardamom plants, Zingiberaceae [1]. However, the supermarket ginger that most people are familiar with is the knobby, root-like rhizome of Z. officinale, better known as the garden ginger.

Fresh ginger gets its pungency and aroma from the flavor compound, gingerol. Studies have extolled gingerol for its many pharmacological abilities, including antipyretic (fever reducer), analgesic (pain reliever), anti-inflammatory, and antibacterial [2]. The best part? Chemically altering gingerol ends up tweaking ginger’s flavor profile, which helps give ginger its flavor versatility. No laboratories or fancy equipment are needed; as long as there’s a kitchen and a love for ginger-flavored foods, fine-tuning the flavor of ginger is rather straightforward.

Heating a ginger rhizome causes gingerol to undergo a reverse aldol reaction, transforming it to zingerone, a molecule that is completely absent in fresh ginger. Like gingerol, zingerone is responsible for the pungency of cooked ginger, but it also lends a sweeter note to the flavor. For this reason, cooked ginger makes a delightful treat as candied ginger. Zingerone also boasts quite a few pharmacological benefits, notably, its many anti-obesity actions [3]. For instance, zingerone was shown to inhibit obesity-induced inflammation, as well as stimulate the release of catecholamine, a hormone that aids in decreasing fat cells [3].

Drying a piece of ginger triggers a dehydration reaction, changing gingerol to shogaol. Shogaol is twice as spicy as gingerol, which is why dried ginger packs more heat than its fresh counterpart. Additionally, shogaol retains gingerol’s bioactivity, reported to act as an antioxidant, anti-neuroinflammatory, and even memory-enhancing agent [4].

With a multitude of benefits and just as many ways to serve it, there’s really no wrong way to enjoy ginger.

References cited

Zingiber. The Plant List (2010). Version 1. Published on the Internet; (accessed 13 August, 2014).
Young H.-Y, et al. Analgesic and anti-inflammatory activities of [6]-gingerol. Journal of Ethnopharmacology. Jan 2005; 96(2):207-210.
Pulbutr P. et al. Lipolytic Effects of zingerone in adipocytes isolated from normal diet-fed rats and high fat diet-fed rats. International Journal of Pharmacology. Jul 2011; 7(5):29-34.
Moon M, et al. 6-Shogaol, an active constituent of ginger, attenuates neuroinflammation and cognitive deficits in animal models of dementia. Biochemical and Biophysical Research Communications. June 2014; 449(1):8-13.

About 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

10 Things About Sushi

September 23, 2014/in Public Lectures/by Grant Alkin

At our 2014 Science of Sushi event, Dr. Ole Mouritsen and Chef Morihiro Onodera illuminated the science underlying some of our favorite components of sushi. In case you still haven’t had your fill, here are 10 scientific facts related to sushi: Read more

The Science of Sushi

September 16, 2014/in Public Lectures/by Grant Alkin

The Science of Sushi
Featuring Dr. Ole Mouritsen and Morihiro Onodera
April 23, 2014

To kick off our 2014 public lecture series, Dr. Ole Mouritsen joined Chef Morihiro Onodera to satisfy our craving for sushi-related science. The duo explained everything from sushi’s early history to the starchy science of sushi rice. Watch the entire lecture or check out some of the shorter highlights below.

Ole Mouritsen on the history of sushi

“The history of sushi is really the history of preservation of food. . . . Throughout Asia, in particular in China and later in Japan, people discovered that you can ferment fish – that is, you can preserve fish – by taking fresh fish and putting it in layers of cooked rice. . . . After some time the fish changes texture, it changes taste, it changes odor, but it’s still edible and it’s nutritious. And maybe after half a year you could then pull out the fish and eat the fish. That is the original sushi.”

Ole Mouritsen on the science of rice

“If you look inside the rice, you have little [starch] granules that are only three to eight microns, or three t0 eight thousandths of a millimeter, big. . . . When you cook the rice, you add some water and the water is absorbed by the rice and [the granules] swell. And the real secret behind the sushi rice is that when they swell, these little grains are not supposed to break.”

Morihiro Onodera on examining the quality of sushi rice

“First what I do is I soak uncooked rice in water. . . . Sometime after 20 minutes it will start to break. . . . I take a sample to check to see if there are any cracks. . . . With good rice, which has less cracks or breaks, you’re able to feel the texture of each of the grains in your mouth, whereas with the lower quality rice you’re just going to get the stickiness [from the starch].”

Food, Wine, and Biochemistry

September 9, 2014/in Science & Food/by Grant Alkin

Photo Credit: Kirti Poddar (22598380@N07/Flickr)

Wine and food pairing may seem like a refined art form, cultivated through trial and error to best suit the individual, but what if we told you there was also a science to it?

When it comes to wines, the word “tannin” is thrown around a lot. In broad terms, tannins are a type of flavonoid molecule, which reside in the bark, leaves, and unripe fruits of a wide variety of plants. The three major classes of tannins are hydrolyzable, condensed, and phlorotannins. Where wine is concerned, phlorotannins are nonexistent (only found in brown algae); hydrolyzable tannins leach from the oak barrel that wines have fermented and aged in; and condensed tannins come from the grapes [1]. While hydrolyzable tannins may be present in all wines, since winemaking traditions necessitate oak barrels, these offer little towards wine taste, mouthfeel, and color. Viniculture favors condensed tannins. Originating from the grape skins, seeds, and stems that go into winemaking, condensed tannins play a key role in wine-tasting.

Red wines are made using the entire wine grape, obtaining their color from anthocyanin, another type of flavonoid molecule found alongside tannins in grape skins. By contrast, white wines are produced from just the grape pulp. Since the tannin-containing parts of the grape do not go into white wine production, white wines are often lower in tannin levels and generally lack condensed tannins.

So how is all this discussion about tannins relevant in choosing which wine to serve alongside a steak dinner?

Tannins contribute to two wine-tasting characteristics: bitterness and astringency [1,3]. Anyone who has ever eaten an under-ripe grape has experienced an exaggerated sensation of astringency, as under-ripe grape skins contain high tannin concentrations. However, astringency should not be confused with bitterness or sourness; these tastes are perceived on the tongue through bitter and sour taste receptors. Conversely, astringency is a physical sensation, frequently described as a dryness or roughness on the tongue.

A sip of wine is just the beginning of the biochemical process behind astringency. Our saliva contains proteins that are able to organize water molecules about themselves, which increases saliva viscosity to above water viscosity, giving rise to “mouth lubrication” [2]. Tannins in wine readily bind to saliva proteins. This causes a snowball effect: tannin-bound proteins end up clumping together with other tannin-bound proteins, creating an aggregate [3]. This aggregate inevitably precipitates out of our saliva. With fewer free, unbound saliva proteins, there is a decrease in saliva viscosity, subsequently leading to a decrease in mouth lubrication [3]. In short, tannins physically dry out the tongue.

In this respect, high-tannic red wines pair well with high-protein foods. With more tannins binding to food proteins, saliva proteins are spared and the wine doesn’t feel as astringent in the mouth. Tried-and-true pairings include Cabernet Sauvignon with a rack of lamb, Pinot Noir with pork roast, and Chianti with grilled salmon.

Besides the protein interactions, tannins have also been shown to favorably bind to fats [4]. Fats are polar molecules by nature (they don’t like to interact with water). On the other hand, saliva is mostly water. By attaching to tannins, fats hinder tannins from mixing with saliva and binding to proteins. Essentially, fats wash the tannins away. For this reason, wine paired with cheese is a great treat, as is a gourmet burger with a glass of Zinfandel.

Armed with this knowledge, why not begin your own wine and food adventure? May we suggest a Cabernet with mac and cheese with spam?

Photo Credit: Jose Tagarao (lidocaineus/Flickr)

References cited

Goode, Jamie. “Tannins in Wine.”Wine Anorak.
Hatton M, et al. Lubrication and viscosity features of human saliva and commercially available saliva substitutes. Journal of Oral and Maxillofacial Surgery. June 1987;45(6):96-99.
Cala O, et al. NMR and molecular modeling of wine tannins binding to saliva proteins: revisiting astringency from molecular and colloidal prospects. The FASEB Journal. November 2010;24(11):81-90.
Furlan, A, et al. Red wine tannins fluidify and precipitate lipid liposomes and bicelles. A role for lipids in wine tasting? Langmuir. May 2014;30(19):18-26.

About 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

Pop Rocks and Carbonation

September 2, 2014/in Science & Food/by Grant Alkin

Photo Credit: Jamie (jamiesrabbits/Flickr)

Some might say one of life’s little pleasures is eating candy. Those who have tried Pop Rocks, however, know that its sugary glory and dare-devilish allure warrant an entirely new adventure. Although it appears harmless, a handful of Pop Rocks candy will set off a fizzy explosion of sugar crystals and popping noises in your mouth. But no remorse is needed; Pop Rocks aren’t actually dangerous. (Mythbusters proves your stomach won’t explode.)

How are Pop Rocks made?

Pop Rocks were developed by scientist William A. Mitchell in 1956 with a technique patented in 1961 to create a revolutionary confection which “enclos[es] a gas within a solid matrix” [1, 2]. Essentially, Pop Rocks is made of a typical hard candy sugar solution (sucrose, lactose, corn syrup and flavoring) with the addition of one important ingredient: highly-pressurized carbon dioxide (CO₂).

First, the sugar solution is heated and melted to obtain a “fusible sugar”. Pop Rocks, like most other hard candies, uses a sugar solution of sucrose, lactose, and corn syrup, because these ingredients produce candy with low hygroscopicity – which means the candy is less likely to absorb water from the surrounding atmosphere [2]. This ensures that the sweet morsels do not dissolve as easily in a humid environment; they are also less sticky and have a longer shelf life.

Just as CO₂ transforms syrupy juice into soda, it will turn ordinary candy into Pop Rocks! The way this works: CO₂ at 600 pounds per square inch (psi) is mixed with the melted sugar until there is about 0.5 to 15 ml of gas per gram of sugar [1, 2]. Note that 600 psi is roughly 7 times greater than the pressure inside a champagne bottle, 20 times greater the pressure in your car tires, and 40 times greater than normal atmospheric pressure at sea level [5, 6].

Photo Credit: Spiff (Wikimedia Commons)

Once the CO₂ is thoroughly incorporated, a process which takes anywhere from 2-6 minutes [2], the mixture is cooled and the candy hardens. Cooling is done as rapidly as possible to prevent CO₂ from diffusing out of the candy, reduce hygroscopicity, and minimize crystallization, a process which makes the candy very fragile. [2] This causes the Pop Rocks to shatter and gives the candy’s signature appearance, “mini rocks” of sugar crystals.

The result? Small candy pieces encapsulating bubbles of high-pressure CO₂. Lo, the magic of carbonation!

Photo Credit: Evan Amos (Wikimedia Commons)

So why do Pop Rocks pop?

When you eat Pop Rocks, the moisture and temperature in your mouth melts the candy. The subsequent popping sounds are a result of the high-pressure CO₂ bubbles being released into atmospheric pressure! But what about the crackling sensations felt in your mouth? Why do we perceive carbonation as a fizzy, tingling flavor sensation?

In the past few years, scientists have identified that taste receptor cells can actually detect and respond to carbonation. Specifically, sour-sensing taste receptor cells are activated in response to CO₂ and are responsible for the “taste of carbonation” [3].

Photo Credit: Bart Heird (chicagobart/Flickr)

The Taste of Carbonation

Sour-sensing taste receptors specifically express a gene which encodes carbonic anhydrase 4, which is an enzyme that catalyzes the conversion of CO₂ to bicarbonate ions (HCO₃^–) and free protons (H⁺). This enzyme is only attached on the surface of sour-sensing taste receptor cells, so when you eat Pop Rocks or drink carbonated soda, CO₂ is broken down and H⁺proton byproducts linger outside of the cell. Since sour-sensing taste receptors activate in response to acidic environments. Therefore, they will detect this abundance of free H⁺ protons and ultimately, detect the taste of carbonation [3].

(A) CO2 is broken down into HCO3- and H+ by the carbonic anhydrase 4 enzyme (B) The abundance of H+ byproducts creates an acidic environment. Through ion channels, the H+ ions enter the sour-taste receptor, which depolarizes the cell and leads to the detection of CO2 .

(A) CO₂ is broken down into HCO₃^– and H⁺ by the carbonic anhydrase 4 enzyme
(B) The abundance of H⁺ byproducts creates an acidic environment. Through ion channels, the H⁺ ions enter the sour-taste receptor, which depolarizes the cell and leads to the detection of CO₂ .

However, carbonation doesn’t always taste sour to us because CO₂ is detected by multiple somatosensory systems in the body. Some researchers even suggest that the tingling, burning sensations associated with the perception of carbonation can be caused by CO₂triggering pain receptors [4].

Would this mean our society’s desire for carbonated food and drink has strangely evolved against a natural aversion to experiencing pain? Personally, I can’t hear over the loud buzzing noises of Pop Rocks in my mouth to find out…and as they say, “no pain, no gain”!

Note: Modified on September 19, 2014
The diagram illustrating taste detection of carbonation has been added in the current post.

References cited

“Why do Pop Rocks pop?” http://www.poprockscandy.com/history.html. Accessed 23 August 2014.
Leon K, Mitchell W (1961) Gasified confection and method of making the same. US Patent No. US3012893 A. Available: http://www.google.com/patents/US3012893. Accessed 20 August 2014.
Chandrashekar J, Yarmolinsky D, von Buchholtz L, Oka Y, Sly W, et al. (2009) The Taste of Carbonation. Science 326: (5951) 443-445. doi:10.1126/science.1174601.
Available: http://www.sciencemag.org/content/326/5951/443.full. Accessed 25 August 2014.
Marziali C (2010) “Sparkling Drinks Spark Pain Circuits”. University of Southern California. http://dornsife.usc.edu/news/stories/796/sparkling-drinks-spark-pain-circuits/. Accessed 26 August 2014.
“Champagne FAQ’s” http://www.champagnesabering.com/home.php?id=16. Accessed 16 September 2014.
“How To Check Tire Pressure” http://www.dmv.org/how-to-guides/check-tire-pressure.php. Accessed 16 September 2014.

About 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

Watermelon

August 26, 2014/in Flavor of the Month/by Grant Alkin

(Steve Evans/Flickr)

Nothing says “summer” quite like a big, juicy slice of watermelon. Even if you prefer it charred on the grill or blended into an icy agua fresca, watermelon is one of the best ways to beat the late-summer heat.

So what gives watermelon its refreshingly delicate flavor?

Turns out the answer is pretty complicated. Over the last few decades, scientists have identified dozens of flavor and aroma molecules that contribute to watermelon’s unique taste [1].

And here’s an interesting twist: a watermelon’s flavor has a lot to do with its color. Chow down on a yellow ‘Early Moonbeam,’ a pale ‘Cream of Saskatchewan,’ or a deep red ‘Crimson Sweet’ and you’ll likely notice different flavor profiles for each melon.

These watermelons don’t just look different, they taste different, too! (David MacTavish/Hutchinson Farm)

Several of watermelon’s flavor molecules form when colorful chemicals called carotenoids break down into smaller chemical compounds [2,3].

For example, the classic color of red watermelons comes from lycopene, the same molecule responsible for the color of red tomatoes. When lycopene breaks down, it forms key flavor compounds such as lemon-scented citral.

Orange melons don’t have much lycopene, but they make up for it with extra beta-carotene. This chemical – the same one that makes carrots orange – leads to a completely different set of flavor molecules, including floral beta-ionone.

Colorful molecules called carotenoids break down into different flavor compounds. Figure adapted from [2].

The chemistry of watermelon flavor is clearly complex, but scientists are still searching for individual molecules that mimic watermelon’s characteristic taste.

Most recently, a study identified a single molecule – dubbed “watermelon aldehyde” – that has a very distinct watermelon aroma [4]. Unfortunately (or fortunately, depending on your perspective), the molecule is too unstable to be used as a food additive. So for now, artificially flavored “watermelon” products will just have to keep on tasting nothing like watermelon.

Good thing there’s plenty of real, chemically complex watermelon to go around.

References

Yajima I, Sakakibara H, Ide J, Yanai T, Hayashi K (1985) Volatile flavor components of watermelon (Citrullus vulgaris). Agric Biol Chem 49: 3145–3150. doi:10.1271/bbb1961.49.3145.
Lewinsohn E, Sitrit Y, Bar E, Azulay Y, Meir A, et al. (2005) Carotenoid Pigmentation Affects the Volatile Composition of Tomato and Watermelon Fruits, As Revealed by Comparative Genetic Analyses. J Agric Food Chem 53: 3142–3148. doi:10.1021/jf047927t.
Lewinsohn E, Sitrit Y, Bar E, Azulay Y, Ibdah M, et al. (2005) Not just colors—carotenoid degradation as a link between pigmentation and aroma in tomato and watermelon fruit. Trends Food Sci Technol 16: 407–415. doi:10.1016/j.tifs.2005.04.004.
Genthner ER (2010) Identification of key odorants in fresh-cut watermelon aroma and structure-odor relationships of cis, cis-3, 6-nonadienal and ester analogs with cis, cis-3, 6-nonadiene, cis-3-nonene and cis-6-nonene backbone structures University of Illinois at Urbana-Champaign. Available: http://hdl.handle.net/2142/16898.

About the author: Liz Roth-Johnson received her Ph.D. in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

Read more by Liz Roth-Johnson

Coffee Brewing Chemistry: Hot Brew vs. Cold Brew

August 19, 2014/in Science & Food/by Grant Alkin

Chemex. Photo Credit: Nick Webb (nickwebb/Flickr)

Hot or cold, temperature won’t stop many from obtaining their caffeine fix. Depending on the weather and personal preferences, coffee drinkers at home can brew coffee by one of two ways: hot brew or cold brew.

Many are familiar with hot brew coffee. The equipments used for hot brew are widely recognized, and even iconic: the moka pot, French press, Vietnamese coffee filter, and Chemex, to name a few. These equipments, as with all hot brew techniques, involve pouring hot water over a bed of coffee grounds, at a general proportion of 1 oz. coffee to 8 oz. hot water [1]. (That’s 2 level tablespoons per 1 cup of water, on a more home-friendly scale.) The resulting liquid, coffee, is then separated from the grounds and ideally consumed as soon as possible.

Left: Moka pot. Photo Credit: Bill Rice (billrice/Flickr) | Middle: French press/press pot. Photo Credit: Bodum | Right: Vietnamese coffee filter. Photo Credit: Marko Mikkonen (markomikkonen/Flickr)

Cold brew demands more patience. In a Mason jar, French press, or Toddy system, coffee grounds are mixed with room temperature water, and then left to sit for hours—anywhere from three to twenty-four hours—before the solids are filtered out. Cold brew recipes often call for a higher coffee to water ratio: 1 part coffee to 4 parts tepid water, which compared to hot brew, is 2 oz. coffee per 8 oz. water (roughly 4 tablespoons per 1 cup water). Once the grounds are removed, what’s left is black coffee concentrate that is thinned with water or milk before it is served.

Toddy System for cold brew. Photo credit: Toddy

On the surface, the distinctions between the two methods seem self-explanatory. Hot brew quickly produces fragrant java with bite and acidity, whereas cold brew rewards patience with condensed coffee that is smooth and sweet. To begin to understand the flavor profile differences, it helps to first get acquainted with the coffee grounds.

Coffee grounds contain a hodgepodge of volatile and non-volatile components, such as various oils, acids, and other aromatic molecules [2]. Collectively, these compounds that are found in coffee grounds are referred to as “coffee solubles” and significantly contribute to coffee flavor [2]. Brewing is the process of extracting these components from the grounds, so coffee beverages are technically a solution of coffee solubles and water. Given that coffee grounds are used in both of our brewing methods, the principle variables are temperature and time.

Temperature affects the solubility and volatility of the coffee solubles. Relative to brewing, solubility describes the ability of the solubles to dissolve out of the grounds and into the water; volatility refers to their ability to evaporate into the air. Coffee solubles dissolve best at an optimal temperature of 195-205°F [3]. With more coffee solubles extracted, hot brew coffees are described as more full-bodied and flavorful when compared to cold brew. Moreover, due to increased volatility with higher temperatures, the aromatics are more readily released from coffee, giving rise to that beloved scent of freshly-brewed coffee.

On the downside, oxidation and degradation also occur more rapidly at higher temperatures. The oils in coffee solubles can oxidize more quickly at elevated temperatures, causing coffee to taste sour. Acids also degrade, the most notable of which is chlorogenic acid into quinic and caffeic acid, causing coffee to taste bitter [2].

Where cold brew lacks in temperature, it makes up for in time. Coffee solubles have markedly decreased solubility in room temperature water. Increasing the brew time from a few minutes to many hours aims to maximize extraction of the solubles from the grounds. Even over twenty-four hours, not all the coffee solubles will have dissolved; this is why the amount of coffee grounds is doubled, in an effort to make up for the lower extraction rate. In comparison with hot brew, cold brew is sometimes described as tasting “dead” or “flat” due to the lower yield of coffee solubles [3]. Further, decreased volatility prevents aromatics from escaping from coffee as easily, so cold brew is much less perfumed than its hot brew counterpart.

Oxidation and degradation will still occur in cold brew methods, but this happens much more slowly; bitterness and acidity are just about absent in cold brew coffee, especially if it is kept cold. Though, cold brew doesn’t merely taste like hot brew without the bitterness. Fans of the cold brew method have emphasized that cold brews contain a completely different flavor profile that can’t be found with hot brews. Going back to the idea of solubility, not all flavor compounds of coffee solubles are equally soluble. A good majority of the coffee solubles are still able to leach out of the grounds, even in colder water. The compounds that don’t dissolve are the ones often attributed to unfavorable flavors [4]: these stay in the grounds that are subsequently tossed away. Consequently, cold brews take on a much sweeter, floral profile.

To note, brew time does not determine caffeine content, nor does bitterness indicate coffee strength. Caffeine is extracted early in the brewing process, so extending brew time, by either method, would only result in over-extracted coffee [1]. Coffee “strength” is defined as the amount of dissolved coffee solubles per unit of coffee volume [1]. On that train of thought, cold brew certainly produces stronger coffee, given that the brewing process purposely concentrates the coffee solubles. Though, keep in mind that rarely anyone drinks cold brew coffee straight up; many enjoy this smooth drink diluted with milk or water.

Whether you’re an adamant hot brew addict or a die-hard cold brew fanatic, at least coffee drinkers can agree that as long as there’s caffeine, everything’s mellow.

References cited

Brewing—How to Get the Most Out of Your Coffee. Mountain City Coffee Roasters.
Sunarharum W, Williams D, Smyth H. Complexity of coffee flavor: A compositional and sensory perspective. Food Research International. March 2014; 62: 315-325.
Giuliano, Peter. “Why you should stop cold-brewing, and use the Japanese Iced Coffee Method.” Dymaxion.
What Everyone Ought to Know About Iced Coffee & Cold Brew. (2012, June 26). Prima Coffee.

About 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

Fruit Salad

August 12, 2014/in Science & Food/by Grant Alkin

Fruit salad can be made throughout the year, but nothing beats a crisp fruit medley on a hot summer afternoon. There are very few limits on what can be a fruit salad ingredient. If the object in question is fruit, it can go in. Segregating fruit from non-fruit seems simple, but from a botanical point of view, classifying these sweet and juicy plant products gets complicated. But, if armed with knowledge and lemon juice, anyone can achieve this delicious and vibrant potluck offering.

Photo Credit: Jo Christian Oterhals (Flickr/jcoterhals)

A fruit is the structure of a plant that bears the seeds. A plant’s flower houses the female reproductive parts, namely the ovary, in the flower’s center. When fertilized, parts of the ovary develop into seeds, and the rest becomes the fruit.

Berries or Not?

The average person defines a berry as anything whose name ends in the suffix, –berry. But to a botanist, a berry is a fruit containing multiple seeds in its interior, embedded in the flesh of the ovary. This includes blueberries, tomatoes, eggplants, grapes, bananas, persimmons, and chili peppers [1]. A botanically-correct berry salad could be very savory; perhaps very spicy.

Blackberries, mulberries and raspberries all fall into the category of berry-imposters called aggregate fruits. Each little bump on a raspberry or blackberry is actually an individual fruit, as each is its own separate ovary, formed from one flower.

Botanically speaking, strawberries are actually not berries. Each pock on the fruit’s exterior is called an achene, and each achene is an individual fruit with a corresponding seed in the interior. The thing we call a strawberry is not a berry in the botanical sense, but rather an accessory tissue for an aggregate fruit (the achenes), formed from multiple ovaries of one flower. [2]

The "seeds" are actually achenes, and they are the true fruit of the strawberry plant (photo credits: flickr/MoHotta18)

The “seeds” are actually achenes, and they are the true fruit of the strawberry plant. Photo Credit: Dome Poon (Flickr/MoHotta18)

Neither Pine nor Apple, and Not a Nut

A  pineapple is considered a multiple fruit. Whereas an aggregate fruit forms from one flower, a multiple fruit is the product of the fused ovaries of a cluster of flowers, thus each pineapple is one large composite fruit. Want to impress guests with a “multiple fruit” fruit salad? Your (somewhat limited) options include breadfruit, osage-orange, fig, and pineapple [3].

Coconut is Not a Nut

Technically speaking, a coconut is a fibrous one-seeded drupe. A drupe is a fruit with a seed enclosed by a hard stony shell, like a peach or olive. An unprocessed coconut has three layers. The smooth, green, outermost layer is called the exocarp. The next layer is the fibrous husk, or mesocarp, which surrounds the hard woody endocarp, which surrounds the seed. A supermarket coconut usually has been freed of its two outer layers. The part most likely found in a fruit salad are just shavings of the seed’s endosperm. This delicious white lining is meant to nourish the seedling coconut tree as it germinates [3].

Both the endosperm and the endocarp visible here. Photo credits: (flickr/su-lin)

Both the endosperm and the endocarp visible here. Photo credit: Su-Lin (Flickr/su-lin)

Keeping Fruit Salad Colorful

Apples, pears, and bananas notoriously turn an unattractive brown after dicing. This is because they contain an enzyme called polyphenol oxidase [4]. When the fruit is sliced, the enzyme is free to react with oxygen, as well as iron-containing phenols in the apple cells that had previously been kept separate. The products of these reactions are ugly, brown chemicals.

The middle of these apple cores have begun to brown. Photo credits: (flickr/Stacy Spensly)

The middle of these apple cores have begun to brown. Photo credit: Stacy Spensly (Flickr/notahipster)

The key to preventing or slowing any enzymatic reaction is denaturing the enzyme. Heat will do the trick, as will reducing the fruit’s contact with oxygen by putting cut fruit under water or vacuum packing it. The simplest way to avoid browning is to apply lemon juice or another acidic substance on the cut surface. Enzymes can only function within a specific pH range, and acidic lemon juice will reduce the pH on the surface of the fruit. For those who fiercely oppose brown apples, try adding add sulfur dioxide [4], a chemical that acts as a preservative by binding to reactants in the fruit to interrupt the browning reaction. For anyone truly passionate about keeping their sliced fruits bright, upgrading to a sharper knife can help. A low quality steel knife may be corroded, and can make more iron salts available for the browning reaction.

References cited

Lloyd, Robin. “Surprising Truths About Fruits and Vegetables.” Live Science. N.p., 22 July 2008. Web.
“Aggregate Fruits.” Fruits Info. N.p., 2004. Web.
“Is a Coconut a Fruit, Nut or Seed?” Library of Congress, 23 Aug. 2010. Web. 10 Aug. 2014.
Helmenstine, Anne Marie. “Why Cut Apples Pears Bananas and Potatoes Turn Brown.” Chemistry.about.com. N.p., n.d. Web. 11 Aug. 2014.

About 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.

Read more by Elsbeth Sites

Vinegar

August 5, 2014/in Flavor of the Month/by Grant Alkin

Making vinegar. Photo Credit: Sharon Mollerus (clairity/Flickr)

Imagine yourself in elementary school parading through the auditorium during your school’s coveted science fair. You round the corner, nearly knocking over the perfectly aligned row of tri-fold poster boards, when you happen upon the fair’s pièce de résistance. Suddenly, science has never been so cool. It’s an erupting volcano! You’re ooh-ing and ahh-ing as you watch the “molten hot lava” spew out from the angry papier-mâché mountain. You inquire about the sour smell in the air and are told by your classmate that this tabletop magic was nothing more than a perfectly planned mixture of vinegar and baking soda.

Vinegar is an aqueous solution that contains acetic acid and water. Historically, vinegars were often produced by exposing wine to contamination by harmless, airborne bacteria known as Acetobacter. Drosophila melanogaster, a geneticist’s model friend, commonly known as the fruit fly, is regarded as a potent vector for the propagation of the bacterium. This particular strain of bacteria facilitates the conversion of ethanol, through aerobic oxidation, into the major component of vinegar: acetic acid. Water is often added to commercially available vinegars to make the substance more suitable for household handling and consumption [1].

The volcano experiment is a simple case of an acid-base reaction where the baking soda, a sodium bicarbonate (NaHCO₃), reacts with acetic acid (C₂H₄O₂) in the vinegar to produce an intermediate product known as carbonic acid (H₂CO₃). The intermediate decomposes and is converted into a carbon dioxide (CO₂) gas, which rapidly escapes from the solution accounting for the reaction’s eruptive characteristic [2].

But enough about chemistry, what about the food?

Vinegar has a plethora of culinary applications and serves as an effective food preservative and delicious sour condiment. From soup dumplings to pickles, vinegar is here to stay! Quite literally, the acidic characteristic (pH less than 4) of vinegar prevents harmful bacterial growth that allows for an extended, indefinite shelf life. So store your vinegar properly and you will be able to keep it for a very long time!

The variety of vinegars is limitless and can be made from virtually anything that contains sugar. Alcoholic fermentation involves the conversion of carbohydrates into ethanol, which can later be converted into acetic acid. One of the most widely available vinegars in the Philippines is coconut vinegar and is made from fermented coconut water. It is typically used to tenderize meat, which is accomplished when peptide bonds in complex protein structuresare disrupted. But it often served as a side condiment to season many different dishes.

Two of my favorite Filipino dishes are called (I) KINILAW (key-knee-lauw) and (2) SISIG (see-seg) and are both prepared with ample amounts of vinegar. The kinilaw is a style of ceviche that infuses ginger and relies on the acidic nature of vinegar to “cook” the fish used in the dish. Lastly, sisig is popular dish in the city of Pampanga and translates to “to snack on something sour”. It is often served with sizzling vinegar marinated pork belly, spicy chili peppers, fresh red onions, cracked egg and native limes to add additional sourness.

Kinilaw: A Filipino-style ceviche cured in coconut vinegar. Credit: Jimmy Sianipar

Fried Potato Chips with Salmon Roe served with Kinilaw. Credit: Jimmy Sianipar

Thrice-Cooked Sizzling Pork Belly Sisig. Credit: Jimmy Sianipar

I recently prepared dinner for 30 friends for my project called PATAO and shared these two delightfully vinegar-y dishes with them! Thankfully no one was a sourpuss and received the dishes with much joy. Check out their reactions here:

[vimeo http://vimeo.com/102508485]

Video Credit: Jimmy Sianipar

References cited

Yakushi T, Matsushita K. Alcohol dehydrogenase of acetic acid bacteria: structure, mode of action, and applications in biotechnology. Appl Microbiol Biotechnol. 2010;86(5):1257-65.
Why does baking soda and vinegar react to each other? UCSB Science Line.

About the author: Anthony Martin received his Ph.D. in Genetic, Cellular and Molecular Biology at USC and is self-publishing a cookbook of his favorite Filipino dishes.

Read more by Anthony Martin