Tuesday, March 26

Cooking with Chemistry: Boiling down the science behind the egg and its role in your kitchen


(Nicole Anisgard Parra/Illustrations Director)

(Nicole Anisgard Parra/Illustrations Director)


Chemistry as a science sounds like something that should strictly be confined to a laboratory with poisonous toxins and exploding reactions, but, as it turns out, most labs aren’t quite like that. In fact, the most important laboratory is found in every home: the kitchen. Understanding the complex processes that go on in the kitchen allows us to go further than the recipe to improve our cooking.

Eggs, one of the most ubiquitous ingredients in cooking, possess such a rich chemistry that they are absolute essentials to any serious chef. An egg’s purpose is mechanical – it mixes ingredients together. Used as emulsifiers and foaming agents, eggs owe their versatility to the fats and proteins that constitute them.

To understand the chemistry of eggs in cooking, we first need to think like molecular-sized architects. Our building materials are primarily carbon, nitrogen and oxygen, and our glue the intermolecular interactions between these atoms.

Intermolecular interactions: It’s all just electric forces

If we want to understand what eggs are doing in our kitchen, we ought to first understand how molecules – a group of atoms connected to each other – interact.

The nature of molecular interactions is electrical in nature. Atoms have a nucleus made of protons and fast-moving electrons that surround the proton. Protons are positively charged and electrons are negatively charged, and we know that opposite charges attract and that like charges repel. This is the key to understanding so much of what happens in the kitchen.

In a molecule, electrons are not confined to their own atoms. They can move around with ease if the right atoms are connected in the right way. Sometimes the movements are so divisive as to polarize the molecule, and sometimes not quite so much that the molecule is not very polar at all. The important thing to keep in mind is that molecules will interact with each other depending on these degree of electrical interactions.

Unscrambling the egg

Eggs are composed of water, fat and, most importantly, proteins. Proteins are interesting chains of amino acids found in nature, and a lot of their behavior is dependent on these electrical interactions.

Using a particular set of atoms as building materials – which are carbon, nitrogen, oxygen and maybe a dash of sulfur – we can construct an amino acid. Start putting them together, and our chains will start to spiral and flatten due to electrical interactions between electrons that move around a molecule and expose positive regions.

Chain enough amino acids and form enough spirals, and the result is an immensely complicated and massive molecule known as a protein. The sheer size of this molecule allows for numerous electric interactions of electrons being attracted toward positive regions or electrons being repelled away from other electrons.

While impressive in its complexity, these massive molecular structures fail miserably under stress testing. Changes in temperature and even physical agitation causes the very particular structure of these proteins to change dramatically, oftentimes irreversibly. While it may sound undesirable, this is exactly what we are doing as chefs. Cooking is, after all, the chemistry of large biological macromolecules.

Brownies, a thermally treated goop of chocolate and sugar

A box of brownie mix consists of sugar, wheat flour, cocoa powder, palm oil, corn syrup, corn starch, a bit of salt, canola oil and some other things. There’s a slight problem: Most of these ingredients can dissolve in water – such as the salts and sugars – but some, like the oils, refuse to interact with the water.

Mixing tends to only work if the electrical interactions are compatible. Oil is large and electrically neutral, and water is small and highly charged. The two are so different that they would prefer to stick to their own kind in a solution.

In the kitchen, this is terrible news. Our brownie solution is soon to be a disaster. Our sugar is in the water and our palm oil in the vegetable oil we added, yet these two liquids won’t mix. We need an ingredient that will bind the two together – something that can mix with both water and oil.

Eggs serve just this purpose because of their key ingredient: proteins. Proteins are amphiphilic, meaning that they have segments that prefer mixing with oil and segments that prefer mixing with water. When mixing an egg, the proteins start to unravel, scooping the ingredients in the water and the ingredients in the oil, creating one large brownie goop. This property makes eggs an emulsifier, also known as a binding agent.

The most important meal of the day

Cooking an egg is a marvelous example of the denaturing process of a protein. Whether the egg is hard-boiled, sunny side up, poached or deviled, we observe the same process of a clear, viscous liquid turned into a delicious white and gelatinous meal.

Egg whites are 90 percent water and 10 percent protein. The major protein is ovalbumin, a particularly sensitive structure. Give it a temperature boost and it starts to fall apart on the molecular level, refolding in an irreversible manner. The protein starts to link up different strands together that it usually wouldn’t at room temperature, creating a cage for the water that was present. The trapped water gives egg whites its gelatinous behavior, but also its white color as the new structure begins to scatter light instead of letting it through. Too much heat and the cage becomes too tight, drying up the gel and creating a rubbery texture.

In order to cook quality soft-boiled eggs, a chef will need to respect the different proteins in the egg whites and the yolk. In boiling eggs, the two most important things are time and temperature. The whites start to cook first as they are the first set of molecules exposed to the heat of the water. The greater the temperature difference, the faster the outsides will start cooking, so for soft-boiled eggs, start with cold eggs in hot water. A strategy to prevent overcooking is to bring your water to a boil, turn off the flame and submerge your eggs, letting the thermal energy take care of the work.

Egg whites are quite versatile due to their tendency to trap things other than just water. When chefs beat egg whites, they physically agitate ovalbumin and open it up. The bundle of proteins begin to grab gas molecules in the air and bubble up, hence why eggs make for fantastic foaming agents in baking.

Understanding the chemistry of the kitchen is fun, but, more importantly, it’s practical. A proper chef understands that the power of an egg lies in its ability to bind all other ingredients together to create a delicious meal.

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  • Mr. Smith

    Poor choice of title pun, since you should never, ever boil an egg.