Plants not under USDA inspection are governed by laws of their states. This numbering system is sometimes used on egg cartons to denote the day the eggs are packed. Fresh shell eggs can be stored in their cartons in the refrigerator for 4 to 5 weeks beyond this date with insignificant quality loss. The color comes from pigments in the outer layer of the shell and may range in various breeds from white to deep brown. The breed of hen determines the color of the shell.
White eggs are most in demand among American buyers.
In some parts of the country, however, particularly in New England, brown shells are preferred. The Rhode Island Red, New Hampshire and Plymouth Rock are breeds that lay brown eggs. Since brown-egg layers are slightly larger birds and require more food, brown eggs are usually more expensive than white. A yellow or greenish cast in raw white may indicate the presence of riboflavin. Cloudiness of the raw white is due to the presence of carbon dioxide which has not had time to escape through the shell and thus indicates a very fresh egg.