On food and cooking the science and lore of the kitchen ( PDFDrive ) 163

egg-leavened cake, then you may be better off with the premium grade, with its thicker white and a yolk membrane less likely to leak foamlowering yolk into the white In any case, the quality of a carton of eggs depends mainly on how old they are Even Grade AA eggs eventually develop flat yolks and thin whites So be sure to check the sellby date stamped on the carton (usually four weeks from the packing date; sometimes the pack date itself is indicated by a single number from 1 to 365), and choose the carton with the latest date Fresh grade A eggs can be a better buy than old grade AA Deterioration in Egg Quality Designed as it was to protect itself for the duration of the chick’s development, the egg is unique among our raw animal foods in its ability to remain edible for weeks, as long as it’s kept intact and cool Even so, the moment the egg leaves the hen, it begins to deteriorate in important ways There is a fundamental chemical change: both the yolk and the white get more alkaline (less acidic) with time This is because the egg contains carbon dioxide, which takes the form of carbonic acid when it’s dissolved in the white and yolk, but is slowly lost in its gaseous form through the pores in the shell The pH scale provides a measure of acidity and alkalinity (p 795) On the pH scale, the yolk rises from a slightly acidic pH of 6.0 to a nearly neutral 6.6, while the albumen goes from a somewhat alkaline 7.7 to a very alkaline 9.2 and sometimes higher This alkalinization of the white has highly visible consequences Because albumen proteins at the pH of a fresh egg tend to cluster in masses large enough to deflect light rays, the white of a fresh egg is indeed cloudily white In more alkaline conditions these proteins repel each other rather than ... is because the egg contains carbon dioxide, which takes the form of carbonic acid when it’s dissolved in the white and yolk, but is slowly lost in its gaseous form through the pores in the shell The pH scale provides a... The pH scale provides a measure of acidity and alkalinity (p 795) On the pH scale, the yolk rises from a slightly acidic pH of 6.0 to a nearly neutral 6.6, while the albumen goes from a somewhat alkaline.. .the egg leaves the hen, it begins to deteriorate in important ways There is a fundamental chemical change: both the yolk and the white get more alkaline (less acidic) with time