Chemical Literacy & Hot Cocoa


In an age where our food supply system grows increasingly complex, chemical literacy is the key to knowing the difference between foods that contain riboflavin versus vitamin B2. With that in mind, let’s take a look at cocoa powder, which is bitter-tasting and impossible to dissolve. To create a sweet, frothy hot cocoa mix from cocoa powder requires some sweeteners, emulsifiers, and…sodium alluminosilicate?
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Fair Food: The Science of Deep-Frying

Image Credit: (flickr/46157135@N06)

Image Credit: (46157135@N06/flickr)

If you spent a single day at the county fair this summer, you’ll agree that the ferris wheels, petting zoos, and live music were all worth the visit. But the most exciting attraction? Fair food.


Image Credit: (jerkalertproductions/flickr)

There are the classics – corn dogs, ice cream, funnel cake – but each year brings new, wacky, unbelievable, and outrageous food creations that only seem justified to consume on a hot carefree summer day at the fair. Many of this year’s jaw-dropping creations were made with the ever so popular method of deep-fat frying.


Classic Funnel Cake. Image Credit: (angryjuliemonday/flickr)

Krispy Kreme Donut Cheeseburger. Image Credit: (flickr/loozrboy)

Krispy Kreme Donut Cheeseburger.
Image Credit: (loozrboy/flickr)

Fried Tornado Potato. Image Credit: (flickr/loozrboy)

Fried Tornado Potato.
Image Credit: (loozrboy/flickr)

Fried Moon Pie. Image Credit: (flickr/davidberkowitz)

Fried Moon Pie.
Image Credit: (davidberkowitz/flickr)

Why do deep-fried foods taste so good?
Various chemical and physical changes occur in deep-frying, including the
Maillard reactionwhich causes the aromatic browning to occur on the crunchy crust of a deep-fried treat. But first, a series of complex processes involving heat and mass transfer must occur between the food and the frying oil.

The process of deep-frying can be divided into four stages: (1) initial heating, (2) surface boiling, (3) decreasing heat transfer rate, and (4) bubble end point [1].  I will henceforth refer to the item being fried as “the food”, whether it’s a Twinkie, or Potato Chips, or Onion Rings, or Bacon-Wrapped Something On-a-Stick.

(1) Initial heating. In the first stage, the food is completely submerged into the hot oil, until the surface of the food reaches the boiling point of water. This stage lasts for about 10 seconds [1]. At this point, the heat from the oil is transferred to the food’s surface by diffusion and also by convection – a process which moves heat due to the bulk circulation of the oil’s currents from a warmer region to the cooler region surrounding the food. While convection uniformly heats the food’s surface, it doesn’t cook the center of the food. Rather, the food’s center is heated through conduction, the process by which heat diffuses from the food’s hot surface into its core through the physical contact of molecules and transfer of their thermal energy. Therefore, convection efficiently heats the food’s surface to facilitate the conduction that actually cooks the inside of the food [2].

(2) Surface boiling. In this stage, we see tiny exploding bubbles sizzling at the surface of the food. Contrary to popular belief, this doesn’t mean that the oil is boiling. Instead, the hot oil surrounding the food causes water inside the food to evaporate, so the little bubbles surface as bursts of steam escaping to the food’s exterior (think jacuzzi steam jets). The movement caused by the bubbling circulates the currents of the frying oil, which increases the rate of heat transfer by “forced convection” and cooks the food faster [1].

Image Credit: (flickr/tibbygirl)

Image Credit: (tibbygirl/flickr)

These steam bubbles are important because they form a “steam barrier” around the food that repels the oil at the surface and prevents the oil from diffusing into the food, which would otherwise turn your crunchy fried treats into a soggy, greasy mess [4]. As the moisture leaves the food, the deep-fried crust we know and love begins to form!

(3) Decreasing heat transfer rate. As the crust continues to dehydrate, it conducts less heat to the rest of the food, so the rate of heat transfer through escaping steam to decreases (reduced bubbling) [1]. The remaining moisture inside of the food is slowly heated to the boiling point of water, which cooks the food inside as if it were boiled, gelatinizing the starch and denaturing the proteins in the food [3]. Now, most of the moisture from the food is lost.

(4) Bubble end point. This is the last stage of deep-frying, in which very few bubbles appear on the surface of the fried food. At this stage, water from inside the food is no longer evaporating, either because all the water from inside the food is gone, or heat transfer from the crust to the core has reduced to the point where it becomes improbable that the water will evaporate [1]. At this point, the fried product should to be removed from the oil, or else the oil will begin to seep into the fried product and make it soggy, since there are no more water vapor bubbles to counteract the diffusion of oil inwards.

Image Credit: (flickr/alexandratx)

Image Credit: (alexandratx/flickr)

Fried ice cream? Fried pizza? Fried Nutella? Armed with the science of deep-frying, the real question is, what can’t you fry?

References Cited:

  1. Farkas, B.E., Singh, R.P., Rumsey, T.R. Modeling heat and mass transfer in immersion frying. I, Model development. Journal of Food Engineering. 1996; 29(2): 211–226.
  2. Zimmerman, B. Heat Transfer and Cooking. Cooking for Engineers, [Online] June 2007.
  3. Alvis, A., Velez, C., Rada-Mendoza, M., Villamiel, M., Villada, H.S. Heat transfer coefficient during deep-fat frying. Food Control. 2009; 20: 321–325.
  4. Greene, A. Back to Basics: The Science of Frying. Decoding Delicious, [Online] May 2013.

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

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Cotton Candy

Summer would be incomplete without carnivals and bright, fleecy, sugary cotton candy. For a snack that’s nothing but sugar and air, there’s a surprising amount of physics and chemistry involved. Below are seven science-heavy facts about this feathery-light confection.

Fotm, cotton candy slide 1

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Fotm, cotton candy slide 7

Editor’s note: The original post stated that 1 ounce of cotton candy is 0.105 kilocalories, when in fact, it is 105 kilocalories, which is equivalent to 105 Calories. Thanks to our astute reader, Allison of the Internet for catching that! The post has now been updated (08-18-2015 10:06 p.m. PST)

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.

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Yeast DNA & Dr. Cotton Candy


Dash Masland was a marine scientist who switched over to beer brewing, using her scientific background to create artworks of the genetic barcodes of the different yeast strains used in various breweries. Over at Vanderbilt University, the Bellan research group is making strides in regenerative medicine using cotton candy and gelatin.
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The Wonders of Baker’s Yeast

Among life’s simplest joys: smelling freshly baked cinnamon rolls wafting through the kitchen, sliding the tray of artfully coiled pastries from a warm oven, and marveling at their golden crust and fluffy interior. An ideal cinnamon roll features a potent cinnamon-sugar mixture oozing in sticky spirals. It’s often topped with a generous smear of tangy cream cheese icing that’s tempered with notes of orange peel and vanilla, sweet and rich enough to catapult you back to childhood. While the filling and icing are notable qualities, what really makes or break a cinnamon roll is its texture. Cinnamon rolls may simply serve as a vehicle for sugar and icing, but their bready foundation boasts an often-understated value. Imagine greedily lunging for a roll and biting into it, only to discover that it’s a rock-hard spiral of disappointment, instead of an airy and delicate pastry with a tender crumb. The science behind the texture of a perfectly fluffy cinnamon roll lies in the yeast.

Photo credit: Mai Nguyen

When you’re browsing the baking aisle in the grocery store, you may be overwhelmed or confused by the sheer number of different forms of yeast available—you’ll find loose granules in packets and jars, bricks, discs, and fast-rising, instant, or active dry. Despite the multitude of forms the yeasts can come in, they’re all merely purified and processed versions of the same organism. Saccharomyces cerevisiae, or baker’s yeast, is a microorganism used in professional and home kitchens alike primarily as a leavening agent for baked goods (1).

The three most commonly/commercially available forms of yeast are:

  • Caked yeast: This moist block consists of fresh, living cells that are packed tightly together. This form of yeast shows substantially higher leavening activity than its dried forms. Caked yeast is highly perishable and has a shelf life of only one to two weeks. More commonly, you’ll encounter yeast granules in packets or jars, widely available as active dry or instant.
  • Active dry: Active dry is a granular form of yeast that has been dried at high temperatures. These granules are comprised of yeast clusters that are encapsulated in a protective coating of yeast debris that formed on the surface of the granules during the drying process. These yeast cells are dormant and need to be rehydrated in warm water before being used. Simply sprinkle the granules in warm water (around 110°F), stir, and wait five to ten minutes. Water will dissolve the protective coating surrounding the granules, releasing the revived yeast cells from within. As the yeast become active, you should see a foamy layer of bubbles forming at the surface, which is carbon dioxide being released.
  • Instant rapid-rise yeast: Boasting higher viability and increased CO2 production, instant rapid-rise yeast is dried at more gentle temperatures than active dry, so more yeast cells survive this drying step. Bakers can add instant rapid-rise yeast directly to the flour, eliminating the need for prehydration. Because instant rapid-rise yeast produces carbon dioxide more vigorously than active dry yeast, these two forms of yeast should not be used interchangeably.

Granules of active dry yeast
Photo credit: Mai Nguyen

Instant rapid-rise yeast
Photo credit: Mai Nguyen

How does this tiny organism transform a dense blob of dough into a puffy masterpiece? To harness its leavening power, we rely on the phenomenon of fermentation. In the first steps of bread baking, water, yeast, flour, and salt are combined. Kneading hydrates the flour and after just a few minutes of manipulation, the dough becomes noticeably stretchier and more pliable. Water enables individual protein molecules in the dough, glutenin and gliadin, to link together to form long, elastic chains of a protein called gluten. These individual gluten strands combine to form a mesh-like network which gives bread its structure and chewy texture (2). Meanwhile, the addition of water also activates enzymes in the flour known as amylases which break down the flour’s starches into simple sugars, providing food for the yeasts (3).

The yeasts feed on these simple sugars and convert them into ethanol and carbon dioxide gas (CO2). This is where the magic begins. As carbon dioxide is released into the dough, it becomes trapped in the gluten matrix. As more and more CO2 bubbles form, the protein network stretches, inflating the dough. Depending on the recipe, dough can spend between an hour to several days rising and can expand two to four times its original size. This initial rising step is often referred to as bulk fermentation.

Like many other types of yeasted breads, a classic yeast-based recipe for cinnamon rolls calls for two rising steps. After the dough has been kneaded and has undergone bulk fermentation, it’s time to roll out the dough and shape it to prepare it for the second rising step, known as proofing. Many recipes for yeasted breads will instruct you to “punch down” dough after the initial rise. In this step, we turn and fold the dough, fill it with a cinnamon-sugar mixture, shape it into coils, and allow them to rise into bloated versions of their former selves (2). This “punching down” or turning step serves a couple of purposes: it stretches the gluten and expels excess CO2 buildup trapped in the dough from the bulk fermentation step, which can inhibit any further yeast activity. Handling the dough at this stage also redistributes yeast, moisture, heat, and sugars throughout the dough for optimal lift and flavor.

A noteworthy point: while our goal is to encourage yeast proliferation and to optimize the production of CO2 and flavor molecules, bakers should be cautious of overfermentation. If yeast fermentation happens too rapidly or continues for too long, gas bubbles can overinflate and burst, causing our dough to collapse (3). The excess of CO2 can also cause the yeast to leave behind many unwelcome tasting flavor compounds and the bread may end up tasting like alcohol.

In our final phase, our twice-risen dough is placed into the oven. Once inside, the dough experiences one last rise thanks to the high heat. The heat causes CO2 present in the dough to expand and for about the first ten minutes in the oven, the rising temperatures stimulate a rapid burst of activity in the yeast, causing them to produce even more CO2. Water and ethanol byproducts in the dough will also expand during heating. This causes the bread to rise dramatically in the oven a phenomenon known as oven spring (3). Eventually, the CO2 and alcohol are expelled from the bread and the yeast cells succumb to a dry, hot death once temperatures exceed 140°F (2).


Photo credit: Mai Nguyen

Behind a cinnamon roll—or any kind of yeast bread —lies an intricate chemistry involved in its creation. Without the wonders of yeast and fermentation, bread wouldn’t exist as we know it today.

References Cited

  1. McGee, Harold. On food and cooking: the science and lore of the kitchen. New York: Simon & Schuster, 1997. Print.
  2. Crosby, Guy. The Science of Good Cooking. Brookline, MA: Cook’s Illustrated, 2012. Print.
  3. Bernstein, Max. “The Science of Baking Bread (And How to Do It Right).”Serious Eats. 1 Oct. 2014. Web. 11 Aug. 2015.

Mai NguyenAbout the author: Mai Nguyen is an aspiring food scientist who received her B.S. in biochemistry from the University of Virginia. She hopes to soon escape the bench in pursuit of a more creative and fulfilling career.

Read more by Mai Nguyen

Jammin’ With Fruit

Now that summer is in full swing, what better way is there to use all the berries, apricots, plums, peaches, and nectarines in season than to make jam? Jam has a great texture that makes it the perfect spread for brioche toast and a sweet complement for porridge. The base ingredients of fruit, sugar, pectin, and acid are cooked until the jam reaches a spreadable consistency [1]. Each ingredient plays an important role in the texture of the final product.

Strawberry jam. Photocredit: Julia Khusainova (Jullclous/Flickr)

Strawberry jam. Photocredit: Julia Khusainova (Jullclous/Flickr)

Sugar Skills

Sugar has many roles besides adding sweetness to the jam. When sugar is mixed with mashed fruit, it begins to dissolve and draw water out of the fruits through osmosis [1]. This occurs because fruit has a lower concentration of sugars than the amount of sugar that is typically added. The hydrophilic groups on sugar make it miscible with other polar molecules like water. Sugar also acts as a preservative by forming bonds with water molecules, making fewer water molecules available to support the growth of various microorganisms that might cause spoilage, such as Aspergillus glaucus and Saccharomyces rouxii [2,3].


The making of blackberry jam. Photocredit: (mrskupe/Flickr)


Pectin is soluble dietary fiber that naturally occurs in certain fruits such as apples, plums, and quinces. When heated and mixed with acid, this carbohydrate creates a thick gel that contributes to the consistency of jam. Acid from citrus increases the hydrogen ion concentration in the solution, which results in the pectin molecules losing some charge. With less electrostatic repulsion, the molecules can now aggregate to form a physical gel at a higher temperature of around 220ºF [4], resulting in watery fruit liquid dispersing itself within a web of pectin molecules [5].

Typically, under-ripe fruits have more pectin because fruit enzymes convert it to pectic acid during the ripening process [5]. This means that high pectin content can often be a trade-off for lower flavor, so it is recommended to use two parts of ripe fruit for every part of under-ripe fruit for the best consistency and taste [1]. Alternatively you can buy powdered pectin from the store to use with fruits that naturally have low levels of this carbohydrate, such as apricots, peaches, and raspberries.

Sugar Inversion

Acid not only contributes to the texture of jam, but it also catalyzes the conversion of sucrose (from added sugar) into its constituent fructose and glucose molecules with the help of heat. This process is called sugar inversion, and it is necessary to prevent recrystallization during jam storage [6]. However, this rarely occurs because finishing a jar of jam usually does not take too long. As an added bonus, acid also contributes to the flavor balance of the jam, preventing it from being too sweet.

Different fruits vary in acid and pectin content, so adjustments may be necessary to obtain the right texture and taste. You can also use a Brix test to measure the endogenous levels of sugars and dissolved nutrients. Basically if your jam contains riper and more nutrient dense fruits, the test will give a higher reading. Develop the right recipe, and you will want to eat out of the jam jar with a spoon!

References cited:

  1. The Science of Jam and Jelly Making. University of Kentucky.
  2. Jam Making: Why all the sugar?
  3. Why does jam go mouldy, even in the fridge? University of Liverpool
  4. Fishman, M.L. & Jen, J.J. Chemistry and Function of Pectins. June 1986.
  5. Jam Making 101. Seriouseats.
  6. Inversion of Sucrose. Colby College.


Catherine HuAbout the author: Catherine Hu is pursuing her B.S. in Psychobiology at UCLA. When she is not writing about food science, she enjoys exploring the city and can often be found enduring long wait times to try new mouthwatering dishes.

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