You can't tell, just by looking at it, how old an egg is. So when you're buying eggs at a store, how can you tell which cartons have the freshest eggs?
You look at the carton.
Cartons have a three-digit number printed on the side, from 001 to 365 — or 366 in leap years. As you have already cleverly intuited, the number corresponds with the number of days that have passed since the beginning of the year. A carton with the number 054 on the side, therefore, would have been packaged on Feb. 23.
These facts, and many more, come courtesy of a brand-new cookbook devoted entirely to eggs, "The Fresh Eggs Daily" cookbook by Lisa Steele. Steele raises chickens in her backyard, so she knows a great deal about eggs, which she happily imparts in the beginning section of her cookbook.
You know that part of a cookbook that no one ever reads? Sometimes it can be worth reading. Steele's introductory section includes such interesting information as:
— Chickens are omnivores; they will eat anything. They don't just eat plants, they eat bugs, worms, lizards and even frogs. If an egg carton is labeled "vegetarian fed," it necessarily means the chickens were kept indoors. Otherwise, they would eat bugs, worms, lizards and frogs.
— Similarly, the phrases "hormone-free" and "antibiotics-free" on cartons are essentially useless terms. In the United States, it is against the law to give hormones to laying chickens, and very few commercial farms use antibiotics.
— If the carton says "cage-free," it could conceivably mean that the chickens are kept in a large warehouse, with their beaks filed to keep them from pecking one another. Even "free-range" could mean they are kept in a large warehouse with an open door to the outside that some of the chickens may never use.
— You can freeze eggs, but not in the shell (the liquid inside will expand, cracking the shell). To freeze, whisk eggs until they are well beaten, then pour them into ice-cube trays coated with nonstick spray (silicone trays work best). Store the frozen egg cubes in a freezer bag for up to six months. Defrost overnight before using.
— Refrigerated eggs will last for three to four months. If kept unrefrigerated, they will be good for two weeks or more. (The book does not say it, but do not leave eggs out for more than an hour if they have ever been refrigerated; bacteria can enter the porous shell when it goes from cold to warm).
— Most supermarket eggs are white because they are laid by Leghorn chickens, which lay white eggs. Leghorns are favored by commercial farmers because they can produce eggs on less feed than many other breeds.
— Chicken eggs can be white, blue, green or tan, and there is absolutely no difference in their nutritional value or taste.
— Eggs are stored pointy end down because that makes it harder for bacteria to get through the slightly alkaline white to the more vulnerable yolk. It also centers the yolk, resulting in prettier hard-cooked or deviled eggs.
— Although eggs are graded by size, they are sold by weight. One dozen large eggs weighs 24 ounces. The eggs inside the carton can be different sizes, as long as they add up to that weight.
— You can separate cold eggs more easily than room-temperature ones. So, separate eggs fresh out of the refrigerator. But then let the whites sit for 30 minutes before whipping them, because:
— Room-temperature egg whites whip better than cold ones. The opposite, incidentally, is true of cream — chilled cream whips faster.
— Anything more than the slightest drop of fat — including yolk — will keep egg whites from whipping into a stiff, airy structure. Before whipping egg whites, make sure there is no yolk (or very, very little), and that the bowl and whisk or beaters are perfectly clean.
— To bring chilled eggs to room temperature, either leave them on the counter for 30 minutes or cover them in tepid water for 10 minutes. (I have had success using lukewarm water for five minutes.)
— If you like scrambled eggs to be soft and dry, salt them before cooking. If you like them to be firm and moist, salt them after they are cooked.