What is Egg Yolk?
Egg yolk, made up of vitelline membrane and yolk, accounts for just under a third of an egg’s total weight. Egg yolks are a highly bioavailable source of the carotenoid lutein, a deep yellow pigment which give baked goods a rich color.1 Egg yolk acts as an emulsifier, keeping moisture in products and tenderizing crumbs. It will also add volume and richness, and acts as a stabilizing agent in confectionary products.
Total Solids in Egg Yolk
Total solid content in an egg yolk falls between 50 and 52 percent. Therefore, when replacing fresh egg yolks with dried egg yolks, use 50% egg yolk powder and 50% water. An egg yolk is mainly composed of neutral lipids and phospholipids (31 percent), and proteins (17 percent) –mostly phosvitin. The yolk’s pH level is around 6. The total solids and pH level in egg yolks are influenced by water migration from the egg white.2
Real Egg Yolk vs. Egg Yolk Powder
The most widely used commercially produced egg yolk comes in two forms: Liquid egg yolk or egg yolk powder. Both begin production the same way. Whole eggs are broken and separated by automated equipment. Liquid egg yolks are then filtered, pasteurized, and other ingredients can be added to improve shelf life. Some of these liquid eggs are then dehydrated into egg yolk powder.3
Dried and liquid egg yolks act very similar in products. Picking which one to use depends on what you are baking. An egg yolk powder may be better with dry mixes or if you have limited chilled storage space, while liquid egg yolk may be easier to work with fresh products.
Eggs have been commercially dried since 1880 and frozen since 1903, and separated since 1912. While both dried and liquid egg yolks begin commercial production similarly, the additives and end process differ.
Liquid egg yolks are mixed with sugar, salt, citric acid or carbohydrates such as corn syrup phosphates. This prevents gelation. Adding 10 percent sucrose or sodium chloride and homogenization also helps stop increased viscosity. Citric acid can be added to prevent greening. Liquid egg yolks are then frozen for transportation and storage.4
Dried egg yolks usually have added silicon dioxide or sodium silicoaluminate to prevent caking. Glucose is reduced, either by an enzyme procedure where a glucose-oxidase-catalase preparation and hydrogen peroxide solution is added, or a yeast procedure, where the pH is adjusted and a controlled fermentation with yeast takes place.4
Keep dried and powdered egg products in a cool dark place, until reconstituted. Then, use right away or keep refrigerated for no more than four days.
Frozen egg yolks can last in the freezer for years. Defrost desired quantities in the refrigerator by placing under cold water, and use immediately. After they are defrosted, store eggs in the refrigerator for up to three days, but do not refreeze.
The FDA groups dried, frozen, and liquid egg yolks all under “egg yolks” on labels. All egg products must labled under the common name of the egg product, such as egg yolks, and list added ingredients. The Food Safety and Inspection Service (FSIS) is responsible for inspecting egg products, with or without added ingredients.
1. Hatta, Hajime, Mahendra P. Kapoor, and Lekh Raj Juneja. “Bioactive Components in Egg Yolk.” Egg Bioscience and Biotechnology (2008): 185-237. Web.
2. Clark, Stephanie, Stephanie Jung, and Buddhi Lamsal. Food Processing: Principles and Applications. N.p.: n.p., n.d. Print.
3. United States Department of Agriculture
4. The Incredible Edible Egg Eggcyclopedia. Park Ridge, IL: American Egg Board, 1999. Print.