106 Principles of Food Science Different cakes have different pH needs. Angel food cakes are the most acidic. Egg whites form a more stable foam when beaten if they are acidic. The color pigment in flour, anthoxanthin, is whiter when the batter is acidic. This pigment is yellowish when the batter is basic. Many angel food cake recipes will call for lemon juice or cream of tartar. These ingre- dients provide sufficient acidity to maximize the volume of the beaten egg whites and promote a snowy white color. Chocolate cakes will have a deeper, darker color and a smoother flavor if they are basic. Devil’s food cake will be light brown at a pH of 7.5. It will be a deep red-brown at a pH of 8.8. This is why chocolate cake recipes will call for baking soda as the leavening agent. Milk or water will give the cake a deeper color than buttermilk, which is more acidic. This is why buttermilk is commonly used in German chocolate cakes, which have a lighter color. See 6-14. Eggs and pH Eggs have porous shells. Carbon dioxide, which is an acidic gas dissolved in eggs, will gradually escape through these shells. As the carbon dioxide escapes, the pH of the egg will climb. Therefore, eggs that have been stored for a while will have a higher pH than fresh eggs. Fresh whole eggs will have a pH of 6.4 to 7.0. Older eggs may have a pH as high as 9.7. The pH, and thus the age, of eggs can affect the way eggs perform in baked goods. Fresh egg whites can have a pH as low as 5.6. These egg whites will be thicker than egg whites from older eggs. The thicker cannot escape. Therefore, ammonium bicarbonate is used only in thin baked goods with a large surface area, such as cookies and crackers. This shape allows the unwanted ammonia gas to escape during baking. Ammonium bicarbonate is only available to commer- cial bakers. It requires ventilation systems to remove ammonia gases. NH 4 HCO 3 NH 3 + CO 2 + H 2 O ammonium bicarbonate ammonia + carbon dioxide + water Batters and Doughs Analyzing batters and doughs before and after baking reveals that pH changes affect the color and texture of many products. For example, the more basic the batter for a particular type of cake is, the flatter and coarser the cake texture will become. Acidity of batters and doughs is affected by the acid mix in the leavening agent. The various acids used in baking powders neutralize or react with the baking soda at different rates. For instance, sodium dihydrogen pyrophosphate is a slower acting acid. Baking powder containing this acid will give batters and doughs a high pH for a long period. On the other hand, monocalcium phosphate is a fast-acting acid. Baking powder containing monocalcium phosphate will give batters and doughs a high pH for a shorter period. The pH of batters and doughs can be altered by adjusting the ingredients. Acidity can be increased by adding various acids such as acetic acid (vinegar) or cream of tartar. Batters can be made more basic by adding baking soda. Optimal pH Ranges for Various Cakes Cake Type pH Range Fruitcake 4.4—5.0 Angel food cake 5.2—6.0 Pound cake 6.6—7.1 Yellow layer cake 6.7—7.5 White layer cake 7.0—7.5 Sponge cake 7.3—7.6 Chocolate cake 7.5—8.0 J. Amendola & D. Lundberg, Understanding Baking, 2nd ed. New York, Van Nostrand Reinhold, 1992, p.129. 6-14 The pH of cake differs from one type to another. Food Fact If you run out of baking powder when preparing a favorite recipe, you can make an ingredient substitution. In place of 5 mL (1 teaspoon) baking powder, you can use 2 mL (1/2 teaspoon) cream of tartar plus 1 mL (1/4 teaspoon) baking soda. You can also use 1 mL (1/4 teaspoon) baking soda plus 125 mL (1/2 cup) buttermilk or other acidic liquid. This substitution will require you to reduce other liquid ingredients in the recipe by 125 mL (1/2 cup). Copyright Goodheart-Willcox Co., Inc.