How Do You Test If Eggs Are Good? | The Water Test Works

You have probably seen the trick before: drop an uncracked egg into a glass of water and watch what it does. If it floats, people say it is bad. If it sinks, it is fine. The test travels by word of mouth, passed along from home cooks and grandparents. But a glass of water can only tell you so much, which raises a fair question — does a sink-or-float result really reveal whether that egg is safe to eat?

The honest answer is mostly yes, with a couple of important caveats. The float test is a reliable indicator of freshness, not a guaranteed food safety check. An egg that floats is almost certainly spoiled and should be tossed. An egg that sinks may still carry bacteria like Salmonella, though the risk is low with properly refrigerated eggs. This article walks through how the test works, how to read the results, and what other steps you can take to be confident before you cook.

How The Water Float Test Works

The science behind the float test comes down to an egg’s porous shell and the air pocket inside it. A freshly laid egg has a very small air cell at the large end — roughly 1/8 inch deep. Over time the egg loses moisture and carbon dioxide through its shell, so the contents shrink and that air cell grows larger.

In a very old egg the air cell can measure over 1/2 inch deep, which makes the whole egg less dense than water. A spoiled egg floats for an extra reason: decomposition produces gases like hydrogen sulfide inside the shell, which further reduces its density. That is also why a rotten egg smells sulfur-like when you crack it open.

To perform the test, fill a bowl or glass with cold tap water and gently lower the egg in without cracking it first. Cold water is important — warm water affects buoyancy and can give a misleading result, so stick with cold tap water for the most accurate read.

Why Testing Eggs Before Cooking Matters

Checking an egg before you cook it serves two practical goals: avoiding food waste and reducing the chance of a bad meal. Tossing a perfectly good egg based on the date alone wastes money and food. Eating a spoiled egg can ruin a dish or, in rare cases, cause illness. The float test gives you a quick verdict without cracking every shell open.

• The sniff test: Crack the egg into a small bowl and smell it immediately. A fresh egg has almost no odor. A spoiled egg gives off a distinct sulfur-like or generally unpleasant smell.
• Visual inspection of the white: A fresh egg has a thick, firm white that stays close to the yolk. An older egg has a thinner, more watery white that spreads out noticeably in the pan.
• The candle test: Hold the egg up to a bright flashlight in a dark room. A fresh egg looks mostly solid inside, while an older egg shows a large, visible air pocket at the wide end.
• Check the carton date: Eggs can often be used safely for several weeks past the sell-by date if they have been refrigerated properly. Use the float test as your primary guide rather than trusting the label alone.

Each method has strengths. The float test is the fastest and least invasive, which makes it the go-to choice for most people. The sniff and visual checks are more definitive but require cracking the egg, meaning you have already committed to using it.

Reading The Results Of Your Egg Test

When you lower a raw egg into a bowl of cold water, one of three things happens. Each result tells you something useful about freshness and whether the egg is worth keeping.

The Australian Eggs industry group explains the outcomes clearly on its fresh egg sinks flat page. An egg that sinks and lies flat on its side at the bottom is very fresh — ideal for poaching or frying, where a firm white matters. An egg that sinks but stands upright on the bottom (pointed end down) is older but still generally considered safe to eat; it should be used fairly soon. An egg that floats to the surface is likely spoiled and should be discarded without cracking.

The upright egg is the result that most people find confusing. It is not spoiled — the air cell has simply grown large enough to tip the egg’s balance in the water. Use it for baking, scrambling, or hard-boiling, where texture matters less than in a fried or poached egg.

Reading the result correctly helps you make a quick decision without ever cracking the shell. The sink-flat egg is your best candidate for delicate preparations. The upright egg works fine for dishes that mask texture. The floating egg belongs in the compost or trash.

Steps For A More Reliable Freshness Check

The float test is a good starting point, but it has limits. A sinking egg could still contain bacteria like Salmonella, although the odds are very low with properly refrigerated, uncracked eggs from a reliable source. For extra certainty, add these simple steps to your routine.

1. Crack into a separate bowl: Crack the egg into a small bowl or ramekin before adding it to your recipe. This lets you inspect it without contaminating your whole dish if the egg has gone bad.
2. Sniff immediately after cracking: Bring the bowl close and take a quick sniff. A fresh egg has almost no smell. Any sulfur-like, fishy, or unpleasant odor means the egg should be discarded right away.
3. Check the white and yolk appearance: Look for a thick, firm white that stays close to the yolk. Reddish or brown spots on the yolk are blood spots — they are safe to eat and not a sign of spoilage.
4. Wash your hands and surfaces: Always wash your hands, utensils, and countertops with warm soapy water after handling raw eggs to reduce the risk of bacterial spread.

These steps add roughly 30 seconds to your cooking routine but provide much more certainty than the float test alone. If an egg passes the sniff test and looks normal, it is almost certainly fine to use. If anything seems off — smell, color, or texture — trust your senses and toss the egg.

What The Float Test Misses

The float test has a few blind spots worth knowing. A hard-boiled egg that floats is not necessarily spoiled — the boiling process itself can create a larger air cell inside the shell, causing even a perfectly fresh hard-boiled egg to float. The float test is only reliable for raw eggs in their shells.

Per the when in doubt discard guide, if you are unsure after the float test, it is safest to throw the egg away rather than take a chance. That rule is especially important for eggs intended for raw or lightly cooked dishes like soft-scrambled eggs or sunny-side-up preparations.

Another limitation: the float test cannot detect Salmonella or other bacteria. A perfectly fresh-looking egg that sinks flat may still carry harmful bacteria if it was contaminated before the shell formed or through a tiny crack. Cooking eggs to 160°F (71°C) kills Salmonella, so fully cooked eggs like hard-boiled or baked dishes are safe regardless of the float test result. Proper refrigeration also slows bacterial growth significantly.

The Bottom Line

The water float test is a simple, effective way to gauge an egg’s freshness without breaking the shell. A fresh egg sinks flat, an older egg stands upright, and a floating egg should be tossed. For the most reliable check, pair the float test with the sniff test and visual inspection after cracking. When in doubt, throwing one egg away is better than risking a meal.

If you have recurring questions about egg freshness or storage practices, the USDA Meat and Poultry Hotline or your local health department’s food safety division can offer guidance specific to your kitchen routine.