The 6 Unstoppable Ways To Tell If An Egg Is Bad (The Float Test Is Only Half The Story)

Knowing how to tell if an egg is bad is a crucial kitchen skill that can prevent food poisoning, save your recipes, and stop you from wasting perfectly good food. As of today, December 15, 2025, the most common test—the simple water float test—is still widely recommended, but experts now agree it only tells you one thing: the egg's age. It does not definitively tell you if the egg is spoiled or unsafe due to bacterial contamination.

The truth is, eggs can remain perfectly safe to eat for weeks, or even a couple of months, past the printed "sell by" date, provided they have been stored correctly in the refrigerator. To truly determine if an egg is safe, you need a comprehensive, multi-step approach that combines the classic tests with crucial visual and technical indicators. Here is the ultimate, updated guide to egg freshness.

The Ultimate 4-Point Egg Freshness Checklist (The 'Uncracked' Tests)

Before you crack an egg, there are several quick, non-destructive tests you can perform to gauge its approximate age and potential for spoilage. These methods rely on the natural aging process of the egg.

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1. The Nuanced Egg Float Test

The float test is the most famous method, and it works because eggshells are porous, allowing air to slowly pass through and moisture to evaporate over time. This process causes the internal air cell to grow larger.

• Very Fresh Egg: Sinks immediately to the bottom of the bowl and lays flat on its side. The air cell is tiny.
• Older Egg (Still Safe): Sinks but stands upright on the bottom, with the wider end pointing up. This indicates a larger air cell, meaning the egg is older, but usually still safe for cooking and baking.
• Bad/Rotten Egg: Floats completely on the surface. A fully floating egg has an extremely large air cell and should be discarded, as it is likely rotten.

The Crucial Caveat: The float test indicates *age*, not *safety*. A floating egg is old, but a sinking egg can still be contaminated if it was stored improperly or its protective outer layer, the *bloom* (or *cuticle*), was damaged.

2. The Unmistakable Sniff Test

The sniff test is, by far, the most reliable and definitive way to determine if an egg is bad. If an egg has spoiled, it will produce a foul, sulfurous odor—often described as a strong "rotten egg" smell—due to the breakdown of proteins.

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How to Perform It Safely:

1. Hold the egg close to your nose while it is still in the shell. If you detect a strong, off-putting odor, discard it immediately.
2. If there is no smell, crack the egg into a clean bowl or plate, away from other ingredients.
3. Take a second, more thorough sniff. If the odor is still present after cracking, the egg is definitely bad and should be thrown out.

3. The Quick Shake Test

Hold the egg up to your ear and give it a gentle shake. In a very fresh egg, the contents are held tightly by the thick *albumen* (egg white) and the strong *vitelline membrane* surrounding the yolk, so you should hear very little or no movement.

If you hear a noticeable sloshing sound, it means the egg white has thinned out and the yolk membrane has weakened, allowing the contents to move freely. This is a sign of an older egg, though again, not necessarily a spoiled one.

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4. The Expiration Date Reality Check

The date on the carton is often a "sell by" or "best by" date, not a mandatory discard date. The USDA considers eggs safe to eat for up to 45 days after packing if they have been continuously refrigerated.

If your eggs have been consistently stored at or below 40°F (4°C), they can often last for weeks past the printed date. However, once that date passes, the other tests become essential.

The Cracked-Open Truth: Visual Inspection & Technical Indicators

Once you've passed the initial sniff test and cracked the egg onto a flat surface, the visual inspection provides the most precise measure of quality and freshness, often used by professional graders.

1. Yolk Appearance and Height

The yolk is a key indicator of freshness. As an egg ages, the *vitelline membrane* that holds the yolk together weakens, causing it to flatten out.

• Fresh Egg: The yolk is high, firm, round, and stands up prominently in a hemispherical shape.
• Older Egg: The yolk is flatter and breaks easily when touched. The color may also appear slightly paler.
• Bad/Spoiled Egg: Look for any discoloration. A rotten egg may have a strange, oily, or black appearance. Do not consume any egg with abnormal colors like pink, green, or black spots, as this can indicate bacterial or fungal growth.

2. Albumen Consistency and the Haugh Unit

The egg white, or *albumen*, is the most scientific indicator of freshness. It is composed of two layers: a thick layer (inner) and a thin layer (outer).

• Fresh Egg: The majority of the albumen is thick, gel-like, and holds tightly around the yolk, creating a distinct mound. This is why fresh eggs are best for poaching.
• Older Egg: The thick albumen breaks down and becomes thin and watery, spreading out significantly across the plate. This thinness is why older eggs are poor for poaching but excellent for hard-boiling.

The Haugh Unit (HU): The gold standard for measuring internal egg quality is the Haugh Unit. This is a calculation based on the weight of the egg and the height of the thick albumen. A higher HU score (e.g., 72+) means a fresher, higher-quality egg.

Advanced Methods and Crucial Safety Warnings

For those who want to be absolutely sure, or for those with backyard chickens, these advanced methods and safety tips add an extra layer of authority to your egg-checking process.

1. The Candling Method

Candling is an old-school technique used by egg graders to inspect the contents of an uncracked egg using a bright light in a dark room. You can use a bright flashlight or a dedicated candler.

By shining the light through the shell, you can observe the size of the *air cell* and the clarity of the yolk.

• Fresh Egg: The air cell is small (about the size of a dime), and the yolk appears dimly defined and centered.
• Older Egg: The air cell is noticeably larger (due to moisture evaporation), and the yolk shadow is more visible and may move closer to the shell.

2. The Salmonella Risk and Refrigeration Rule

While an egg may be old, the primary danger is not age but bacterial contamination, specifically *Salmonella*. This bacteria can be present inside or outside the egg, and poor storage increases the risk significantly.

The FDA and USDA Rule: Always store eggs in the main compartment of your refrigerator (not the door, where temperatures fluctuate) at a consistent temperature of 40°F (4°C) or below. Refrigeration is paramount for safety.

3. When to Absolutely Discard an Egg

Regardless of the float test or the date on the carton, you must discard an egg immediately if you observe any of the following signs:

• Foul Odor: The overpowering sulfur smell.
• Shell Damage: Any cracks or sliminess on the shell, which allows bacteria to enter.
• Discoloration: Black, green, pink, or iridescent spots in the egg white or yolk, which indicate bacterial or fungal growth.
• Cloudy Egg White: This is a sign of carbon dioxide, which is actually an indicator of a *very fresh* egg, not a spoiled one. The cloudiness will disappear as the egg ages.

By combining the physical tests—float, sniff, and shake—with the detailed visual inspection of the yolk and *albumen* consistency, you can confidently determine the freshness and safety of your eggs. While the float test is a good starting point, the ultimate judge of quality remains your nose and your careful visual inspection of the cracked contents.