Eggs: Chemical Properties and Functions in The Baking Process

The smell, taste, and sensation of a freshly baked cookie is uniquely powerful; it is tied to fond memories and watering mouths for many people the world over. What the average person might not know is that the very things that make a cookie appetizing are due to chemical reactions, many of which are facilitated by the inclusion of eggs as an ingredient in the baking process. However, more and more people each year are avoiding eggs in their diet for various reasons. The vegan lifestyle is getting more affordable and commonplace. Fears (the rationality of which are still heavily debated) of rising cholesterol from egg consumption also contribute. Furthermore, an allergy to eggs is the second most common allergy in children behind milk products (FARE). How is one to create a familiar, delicious cookie without the use of eggs? This paper seeks to discern the chemical properties of eggs, their specific functions in the baking process, identify some substitutions that serve similar purposes, and uncover how they chemically fit the role.

In the average cookie, eggs may seem like a small proportion of the ingredients by volume, but their chemical properties affect how all of the other ingredients work together to create the final product. So, what is an egg? The average chicken egg regularly used in American household baking is composed of a hard outer shell that can come in a variety of shades, the white, and the yolk. After cracking the calcium carbonate (CaCO3) shell, the baker first comes in contact with the white, or albumen, which is approximately 90% water with the rest being seven major proteins (Evanhoe 2006). The most prominent of these is ovalbumin, which provides nourishment and assists with immunity for the unborn chick. Conalbumin is necessary for binding iron. Approximately 2% of the protein in the egg white is ovomucin, responsible for its familiar thickness and goopy consistency. The pH of the albumen in a freshly laid egg is approximately 7.6, rising to 9.2 after days of storage. Albumen adheres to the inside of the eggshell more strongly at a lower pH. The yolk can be yellow to even almost red in color due to the carotenoid pigments lutein and zeaxanthin. The yolk contains approximately 33% lipids and 17% protein. It contains a significant amount of fatty acids (including oleic acid, palmitic acid, and linoleic acid) and some cholesterol. It also contains fat soluble vitamins A, D, E, and K, and the compound lecithin, which contains many different phospholipids. Lecithin is notable for being an emulsifyer, stabilizer, and surfactant. It is extracted from eggs for many uses including pharmaceutical purposes and some cosmetics (Pyler 2010). These same properties make eggs valuable in baking as well.

When beating eggs into flour, butter, and other cookie ingredients, it may appear as though the purpose is only to combine items together into a more homogenous mixture, but really the chemistry of cookies is already unfolding. Eggs assist in bringing the water and fat phases together to result in a creamier and smoother texture (Indrani 2008). The lecithin from the yolk coats air bubbles that arise during beating, preventing them from collapsing when heated. These fat coated air bubbles of CO2 increase the fluffiness of the final product and contribute to rise, structure, and shape. Lecithin and other long amino acid chains from the egg act as binders to hold ingredients together. Once baked goods reach an internal temperature around 176 degrees F, the risen batter adopts its permanent shape as the egg proteins coagulate, the starch granules absorb water and form a gel, and the gluten denatures and loses its elasticity. The final texture is set during baking by the coagulation of the egg and flour proteins (Connelly2010). One of the most important chemical reactions in baking is the Maillard reaction, commonly known as just “browning,” but responsible for the right golden brown color of doneness and producing hundreds of toasty and savory aromatic flavor compounds. The right temperature is required for the sugars and proteins on the surface of the baked goods to combine and rearrange into the right compounds. The reactive carbonyl group of the sugar interacts with the nucleophilic amino group of the amino acid. This process accelerates in an alkaline environment because the amino groups do not neutralize. At a higher pH, the amine group is a better target for reducing sugars. Egg wash applied to yeasted bread or other baked goods raises the pH of the surface to further encourage the Maillard reaction. The fat, sugar, albumen, and other protein content leads to nearly unparalleled potential in the kitchen to boost the potential of the other ingredients around them by thickening, binding, leavening, providing structure, contributing moisture, and encouraging the Maillard reaction (Gillespie 2019). Additionally, eggs thicken and smooth custards and puddings and create stable foam at high temperatures that allows for delicate choux pastry and meringues (Tamanna et al 2015).

Given the unique structure and contents of an egg, it is easy to imagine how difficult it would be to replicate in baking. So, what can you do if you’re avoiding eggs for ethical, dietary, or allergen concerns? The good news is that not all hope is lost. Several items that function in similar ways to eggs in baked goods have been identified, and there are a few commercially available products on the market known as egg replacers. However, the bad news is that no such item on earth exists that can do exactly what an egg can do while being vegan or egg-allergen free. But, if you can identify the main physical and chemical property that an egg is meant to bestow upon your recipe, there are some specific alternatives that can readily and often indistinguishably take its place.

The emulsifying properties of eggs are the easiest to emulate (McVean 2018). These are recipes wherein the egg serves to stabilize a mixture between two immiscible liquids, like the process of making mayonnaise, or creaming fat and sugar together when making a pound cake. The main factor affecting emulsifiers is concentration, with dilute ingredients emulsifying poorly. The most ideal substitutions for eggs in emulsions is flax seed. The outermost layer of flax seed, the epiderm, contains a mucilaginous material which makes up about 8% of the flax seed by weight. This mucilage, or gel, once drawn out, can be readily utilized as an egg replacement that is suitable for many vegan baking applications. How? Flax gel is a hydrocolloid, composed of polysaccharides. While eggs themselves contain almost no carbohydrates, the long chains of simple sugars found in flax gel can form extensive networks similar to those of denatured egg proteins (Noren). While other plants such as chia seeds, aloe vera, okra and even some basil seeds also contain polysaccharide gels, they can in some cases be cost prohibitive and in other cases impart unwanted flavors to the final product. Of course, flax gel can’t do everything that an egg can do. It will not successfully replace eggs in extremely airy desserts like angel food cake, choux pastry or popovers. In cakes, flax gel would likely not be a good substitute because the mucilage can coat the gluten and gliadin in the flour, effectively blocking gluten bonds from forming, so it won’t build structure like an egg would (Hagedorn 2019). However, in things like muffins, breads, and cookies, a “flax egg” will work well. There are a few methods for creating a “flax egg.” The simplest is to grind whole flax seeds in a blender or spice grinder, then 1 tablespoon of the ground flax meal to 3 tablespoons water. Allowing this mixture to sit for 10 minutes will release the mucilage. Warmer water speeds up this process. The whole thing can be added in recipes in place of one egg, in recipes where the color and texture won’t be an issue. Miyoko Schinner, celebrity vegan baker and CEO of Miyoko’s Creamery, is credited for pioneering an alternative, more involved method, which ought to be used in instances where the aforementioned color and texture would not do (Hagedorn 2019). Instead of grinding the flax seeds, one can boil 5 tablespoons of flax seed in 3 cups of water for approximately 20-25 minutes. Not only does this method extract all the mucilage from the hull, boiling off some of the water allows the mixture to condense somewhat. Then, using a fine sieve, strain the mucilage from the water and allow it to cool. Due to its viscosity it can be difficult to measure, but three tablespoons is the working conversion rate to replace one egg.

Coagulation is a bit more difficult to replicate perfectly. This property enables eggs to bind foods together, thicken applications, such as custards, omelets and puddings or positively benefit the crumb and structure of baked goods (Pyler and Gorton 2010). In things like corn bread, quickbread, or vegan burgers, for example, a common recommendation is to add extra starch such as arrowroot powder, potato starch, or tapioca starch, and some neutral oil for additional fat. Another common recommendation is the additional of mashed fruit such as mashed bananas, applesauce, mashed potatoes, pumpkin or squash purée. Here it very much depends on the desired flavor of the final product. Applesauce provides very little in the way of flavor and texture in baked goods while a little bit of banana can overpower a recipe. The egg replacement of choice will vary dramatically depending on the recipe and the personal preferences of the baker.

The most difficult property of an egg to reproduce for vegan or otherwise egg-avoidant baking until recently was foaming. You can’t make a meringue out of a banana. An ingredient’s ability to foam is affected by the method of beating, temperature, pH and water content. Some foods such as soy milk or whey protein can create foams, but these foams are not stable at high temperatures. The savior ingredient of vegan bakers everywhere was brought to public attention in 2015 and dubbed aquafaba, translated literally from Latin to “bean water,” because it is the would-be discarded liquid one finds in canned chickpeas (Danovich 2017). It is completely vegan, and manages to create temperature resistant foam. This is made possible because during the cooking process when chickpeas are canned, water soluble proteins and sugars from the beans are leeched into the surrounding water, accounting for approximately 5% of the dry weight of the chickpea being lost. The exact chemical makeup of aquafaba is under review, and little conclusive scientific data exists today about its exact chemical structure and properties. While there is still little conclusive scientific data on the actual nutritional value and content of aquafaba, one study posits that additives in canned chickpeas such as salt and disodium EDTA might suppress its viscosity and ability to form stiff peaks, so egg-free bakers should be aware of the contents in their canned chickpeas before using (Shim et al). Some smaller studies have found that aquafaba contains the polysaccharides amylose and amylopectin, sucrose, and some proteins that make the liquid similar in texture to egg whites. Aquafaba also contains saponins which produce foam when whipped very similar to an egg. However, there is no concrete data on how this varies by brand. Many vegan recipes suggest that the liquid from one can of chickpeas is the conversion for one egg in a recipe.

In conclusion, while eggs are impossibly complex little power houses of chemistry in the kitchen, there are many reasons one might wish to omit them from baked goods and even more ways to do so. However, in order to properly replicate the presence of egg in a recipe, one must first identify the main purpose for the egg and find the right replacement to mimic it. While using replacements for eggs in baked goods does make the final product different in some ways from the original, with some ingenuity, egg-free baked goods frequently taste as good or potentially even better than the originals.

Works Cited

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