Store-bought eggs should carry a Grade A or Grade AA stamp as well as date of grading and freshness code. Grades AA and A are the top two classifications of the USDA's voluntary system for indicating an egg's quality. They have no bearing on size or freshness. Rather, both indicate eggs that had high, round yolks and firm, thick whites when they were first laid. While AA-graded eggs are a bit more shapely, the difference between the two grades is slight, and with age, no matter what its grade, an egg yolk will flatten out and the white will turn watery.