While whole eggs, yolks and egg whites all supply practical benefits to baked goods, it is egg whites that achieve a lofty, stable foam for aeration or a leavening effect. In fact, egg whites, when whipped, can produce foam six to eight times greater in volume than the original liquid. These foams help aerate many different types of popular baked goods—including angel food cake, sponge cake, layer cakes, cookies, meringues and even hearth-baked breads and rolls.
Aeration is referred to as a critical function when formulating baked goods. It basically means that a gas, or air, is being introduced into the liquid batter. Beaten egg whites supply a highly effective1 leavening agent that helps incorporate air into the dough or batter.
Cake batter is considered a mobile foam and baked cakes a rigid foam. In order to become this rigid foam, the air bubbles must remain trapped in the batter and expand during the baking process. This step of trapping air in the batter during baking helps cakes (and other baked goods) rise. A proper rise increases product volume (height) and produces a lighter texture (density), impacting the finished product’s visual appearance, as well as mouthfeel and other sensory properties.
The Protein Connection
Although egg whites contain some of the eggs’ high-quality protein, as well as riboflavin and selenium, the majority of an egg’s nutrient package is found in the yolk. Containing ~40% of the egg’s total protein, the yolk contains the majority of the vitamins and minerals in the egg like vitamin D, B12, choline, selenium and the carotenoids lutein and zeaxanthin.
More than 40 proteins are present within eggs.1 While the egg yolk contains about 40% of the egg's protein, the egg white is almost entirely made of protein. The complex interactions among the various proteins in its makeup supply the source of egg white foaming ability. Part of the unique nature of the aerating qualities of egg whites is not just foam formation, but also its stability.
While whipping egg whites, air bubbles decrease in size and increase in number, surrounded by egg proteins. Liquid egg products have low air-liquid interfacial tension, therefore when eggs are beaten or whipped, the proteins denature or unfold. This exposes two oppositely charged ends of the protein molecule: the hydrophobic, or water-hating end, and the hydrophilic or water-loving end. The proteins bond during foam formation, and when heat is applied coagulation occurs which sets the foam preventing further movement of gas and liquids. The result is a delicate, yet reinforced network that encases the air micelles.2,3
During baking, the liquids within the baked good turn to steam and this steam pushes on the walls of the air cells to expand them, giving products their rise. The egg proteins coagulate with and form a network with gluten and other food components, setting the walls of the air cells to hold the product shape as it cools.4
Examining the particular proteins that contribute to this function, one finds that albumen protein constituents, such as the globulins, contribute most to the egg white foaming ability, followed by ovalbumin and ovotransferrin. In terms of stability, the protein ovomucin enhances foam stability by forming a membrane that prevents thinning of the liquid or drainage.5
Some studies have shown that lysozyme has a greater effect on foam stability than ovalbumin, particularly when lysozyme is preheated. This creates the finest, most homogeneous and stable foam texture with the slowest drainage.6
The pH value of the egg white can be adjusted to help optimize foam stability and cake volume.1 Specifically, adding an acid to the batter (e.g., cream of tartar) helps strengthen and stabilize an egg foam. While egg white products are available in three different forms — frozen, liquid or dried — one caveat for dried egg white is that it should be “whipped to a stiffer and drier peak than when fresh or frozen egg white is used.”1
Specialty Baked Goods
The combination of the proteins within egg ingredients and the capability of egg whites to aerate products finds application outside of traditional baking channels to positively influence gluten-free baking formulations. Gluten-free flour often involves a combination of rice, tapioca, corn, or potato starches. These contain a lower protein content than a traditional wheat flour-based baking flour blend, necessitating formulary adjustments related to dough viscosity and rheology.
Low loaf volume is still an issue in gluten-free baking.7 Egg aeration, in addition to processing adaptation, can assist with whipping air into the dough or batter. In just one product example, a researcher noted “Egg ingredients contribute both proteins and functional properties, such as air-micelle formation binding and humectancy in gluten-free wafers and waffles.”8
Regardless of the product application, whether a traditional baked good or one serving a specialty market, the foaming ability of egg white can aid in proper product aeration. This leads to beneficial functional, visual and sensory aspects that improve dough viscosity, processing and machinability, and end product texture, appearance and mouthfeel.
More Egg Science
If you’re interested in learning more about egg science and its role in food product development, the American Egg Board created the EggPro™ curriculum – a professional development course with an e-learning module on the science of egg functionality. This course was designed specifically with food scientists and culinogists in mind. It’s tuition-free until the end of 2020.
Get more details at rouxbe.com/eggpro.
Elisa Maloberti is Director of Egg Product Marketing at the American Egg Board
About the American Egg Board (AEB)
Home of the Incredible Egg, the AEB is the U.S. egg industry’s national commodity marketing board. The AEB’s mission is to increase demand for eggs and egg products through research, education and promotion. The AEB’s Egg Nutrition Center is the country’s largest repository of egg nutrition research.
The AEB is located in Chicago, Ill. For more, visit www.incredibleegg.org.
1 Pyler EJ and Gorton LA. (2010). Baking Science & Technology, Fourth Edition, Volume 1, Sosland Publishing Co., Kansas City, Missouri, USA
2 Stadelmen WJ and Cotterill OJ. (1995). Egg Science and Technology, Fourth Edition, Haworth Press, Inc., New York, USA
3 American Egg Board. (2012). “Aeration in Baked Goods” YouTube, narrated by Shelly McKee, Ph.D., Associate Professor, Department of Poultry Science, Auburn University, Auburn, AL; Feb. 29, 2012 https://www.youtube.com/watch?v=JdzJizdIZYg
4 Brown A, Understanding Food: Principles and Preparation, Third Edition, Cengage Learning
5 Hui YH, Corke H, De Leyn I, Nip WK, Cross N (2014). Bakery Products: Science and Technology, Second Edition, John Wiley & Sons, Ltd.
6 Hagolle, N, Relkin, P, Popineau, Y, and Bertrand, D. (2000). Study of the stability of egg white protein-based foams: Effect of heating protein solution. Journal of the Science of Food and Agriculture. 80. 1245 - 1252.
7 Elgeti, D, Jekle, M, and & Becker, T. (2015). Strategies for the aeration of gluten-free bread - A review. Trends in Food Science & Technology. 46. 10.1016/j.tifs.2015.07.010.
8 Tiefenbacher K (2017). The Technology of Wafers and Waffles 1: Operational Aspects, Academic Press, Elsevier, London, England