Eggs are a highly perishable food item, but they can remain good for several weeks beyond the printed date if stored correctly. The primary concern is distinguishing between an egg that is merely old and one that has developed harmful spoilage, which requires using simple home tests. Understanding the natural changes that occur within the egg allows consumers to accurately gauge freshness and avoid food waste.
Immediate Freshness Tests
The most common and effective way to determine an egg’s age is the float test, which relies on the fact that eggshells are porous. As an egg ages, moisture slowly evaporates through the shell, and the lost volume is replaced by air, causing the air cell at the blunt end to expand. To perform the test, gently place the egg in a bowl of cold water deep enough to cover it.
A very fresh egg will sink immediately and lie flat on its side at the bottom, indicating a tiny air cell. If the egg sinks but stands upright on the bottom, it means the air cell has grown larger, but the egg is still of good quality and should be used soon. An egg that floats to the surface has a large enough air cell to make it buoyant and is likely significantly older, though it may not be spoiled.
The plate test, which involves cracking the egg onto a flat surface, provides a visual assessment of internal structure. A fresh egg will have a firm yolk that sits high and round, surrounded by a thick, compact egg white, or albumen, that does not spread far. The thickness of the albumen is an indicator of quality; the higher the albumen, the fresher the egg.
As the egg ages, the thick albumen structure breaks down, causing it to become runnier. This results in an older egg having a flattened yolk and a thin, watery albumen that spreads widely across the plate. While lower in quality and not suitable for poaching or frying, this egg is usually still safe to use in baking or fully cooked dishes.
Recognizing Absolute Spoilage
While the float test indicates age, the most reliable method for detecting absolute spoilage is the sniff test, which should be performed immediately after cracking the egg. A rotten egg produces a distinct, foul odor, often described as sulfurous or pungent, due to the presence of hydrogen sulfide gas produced by bacteria. If any odor is present, the egg should be discarded immediately, even if it passed the float test.
Visual inspection after cracking is also important, as spoilage can manifest as discoloration. The egg white, which is normally clear or slightly cloudy, may appear pink, green, or iridescent, a sign of contamination by Pseudomonas bacteria. Any black or green spots on the yolk or white can indicate fungal or bacterial growth, and these eggs must be thrown out.
Before cracking, examine the shell for any signs of damage or contamination. A cracked shell allows bacteria to enter the egg more easily, and a slimy or powdery exterior can signal the presence of mold or bacterial growth. If the shell is compromised, it is safest to assume contamination and discard it.
Maximizing Shelf Life
Eggs are typically safe to consume for up to three to five weeks beyond the “Sell-By” or “Best-By” date printed on the carton, provided they have been stored properly. These dates are indicators of peak quality, not absolute safety limits. The “Pack Date,” often printed as a three-digit Julian date, is the most accurate measure of the egg’s true age.
Storing eggs in the refrigerator at a consistent temperature of 40°F (4°C) or lower significantly slows the deterioration of quality and growth of bacteria. It is beneficial to keep eggs in their original carton, as the cardboard protects them from absorbing odors from other foods through the porous shell and helps maintain a stable temperature.
Avoid storing eggs on the refrigerator door, as this area is subject to the most frequent temperature fluctuations, which can accelerate the breakdown of the albumen. Placing eggs with the pointy end facing down helps to keep the yolk centered and away from the air cell at the blunt end, which reduces the risk of microbial contamination.