Chapter 6 Ions: Charged Particles in Solution 107 an egg white is, the more air it will trap and the greater volume it will attain when beaten. This means fresh egg whites will produce higher meringues and lighter angel food cakes. Adding cream of tartar to egg whites will also produce these qualities by lowering the pH. See 6-15. The loss of carbon dioxide does not seem to affect the egg yolk. Yolks will maintain a fairly stable pH for several weeks. Older eggs have their advantages. The loss of carbon dioxide releases the membrane around the egg white from the shell. Hard-cooked eggs will peel easily if they have been stored for several days before cooking. Fresh eggs are very difficult to peel without tearing the egg white. pH and Fruit Maturity As fruits mature, acids develop. These acids aid in the production of the fruits’ characteristic flavor compounds. The acids improve juice quality, affect color development, and help increase sugar content. As ripening progresses, some acids are neutralized as others develop or increase. The ideal pH and the acid mix are different for each type of fruit. Testing pH levels plays an important role in determining harvest time for many fruits. The pH of grapes is critical to successful wine making. Growers carefully test the pH of grape samples to see if the grapes have reached optimum pH. The flavor of citrus fruits is a delicate balance between the sweetness of sugars and the sourness of acids. As citrus fruits ripen, sugars increase and acids decrease. The ripening process and the changes associated with it stop once citrus fruits are picked. Therefore, citrus growers test the pH of fruits to determine when to harvest for peak flavor. The ideal mix of sweet and sour is different for every variety of citrus fruit. The ideal mix also varies, depending on the month and the location. To assist growers, food scientists have created charts showing the best ratios of sugars and acids for different citrus fruits. pamela_d_mcadams/iStock/Getty Images Plus 6-15 To get a snowy white angel food cake, add lemon juice or cream of tartar to lower the pH. Copyright Goodheart-Willcox Co., Inc.