Navigating various dates on foods such as "sell by," "best by" and "expires on" can be confusing. With their neat, natural shell packaging, eggs may seem even more difficult than average to check for spoilage. In reality, eggs have a lengthy shelf life, and it is quite easy to tell if they've gone bad, so baking or cooking with them after the "use by" date isn't generally a problem.
U.S. Department of Agriculture guidelines require that all eggs be marked with what is called a Julian Date. A Julian Date is a code that consists of three numbers corresponding to the actual day of the year; for example, January 1 is 001 and December 31 is 365. It is important to note that the USDA doesn't actually require an expiration date on eggs, but all eggs that are stamped with a "use by" date must be dated within 45 days of the package date. According the the Georgia Egg Commission, a properly stored egg can be expected to stay fresh for at least a couple of weeks post expiration date.
As time passes, the body of the egg slowly diminishes. Fresh egg yolks stand taller and the whites are thick when they are cracked open, while older eggs seem watery and thin. These eggs are perfectly safe to eat, though they may not create the perfect sponge cake. Fresher eggs "stand up" better for whipping and create a better rise in baked goods. One simple way to test for freshness is to put eggs into a pot of water. Fresher eggs will sink to the bottom, and old eggs will float due to evaporation through the porous shell over time.
Proper storage techniques will increase the shelf life of eggs. Eggs should always be stored cold and not at room temperature unless you are using them immediately. Eggs can also be frozen with little loss of quality. Crack eggs into freezerware or baggies first, then freeze. Be sure to freeze in appropriate portion sizes, as they should be used within three days after they are defrosted. Previously frozen eggs can still be used in baking -- including whipping -- with little loss of quality.
The only true way to tell if an egg is rancid is to crack it open. A rancid egg will smell bad and have an off color. There is a very real possibility of ruining an entire recipe with a rancid egg if it's accidentally cracked into already mixed ingredients. The best way to avoid this is to crack an older egg into a small cup first to check it, then add it to the recipe.
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