Egg Freshness Checker: How Long Duck Eggs Keep, and What the Float Test Means

There is a duck egg on the counter and nobody remembers when it was collected. The float test is what most people reach for, and the float test measures the wrong thing. This checker takes what you do know — when it was laid, whether it was washed, where it has been — and gives the storage limits the USDA and Penn State publish for that egg, and then explains what a floating egg actually tells you.

Key takeaways

• USDA: raw eggs in the shell keep 3 to 5 weeks refrigerated. Penn State: at least a month. Hard-boiled: one week.
• An unwashed egg keeps its bloom, the natural seal on the shell. A washed egg has lost it and must be refrigerated.
• The float test measures the size of the air cell — age, not safety. It tells you an egg is old, never that it is safe.
• Neither body publishes a duck-specific figure. The checker does not invent one.

What the checker does

You enter the collection date, whether the egg was washed, whether it has been in the fridge or out, and whether it is raw or hard-boiled. The checker works out the age in days and matches it against the published limits for that case. A raw egg in the fridge inside three weeks is inside the published guidance; between three and five weeks it is inside the USDA’s range and near its end; past five weeks it is outside the published guidance, and the checker says plainly that it cannot call the egg safe. An egg whose collection date you do not know gets the same honest answer: it cannot be assessed.

A hard-boiled egg gets the USDA’s one week, counted from the day it was cooked, if it went into the fridge within two hours; out of the fridge there is no figure beyond those two hours for a boiled egg at all, because boiling strips the bloom entirely. A washed raw egg kept at room temperature gets the plainest answer on the page: it should have been in the fridge.

The bloom, and why washing matters

A duck lays an egg with a cuticle on the shell — the bloom — that seals the pores against bacteria and slows water loss. Penn State’s guidance for home flocks explains that this is what protects the egg; the USDA’s Food Safety and Inspection Service says it is not necessary or recommended for consumers to wash eggs, because washing can draw water and whatever is in it through the pores into the egg.

So an unwashed egg and a washed egg are different objects. Unwashed, with the bloom intact, eggs are sold unrefrigerated across much of Europe on this principle, and in the fridge an egg keeps for the full published period. Washed, it must be refrigerated. No US body publishes a room-temperature shelf life for an unwashed egg, so the checker gives none and cannot say whether an egg kept warm is safe.

Duck eggs are dirtier than hen eggs — laid on the floor, in wetter bedding, by a bird that walks through water — so the washing question comes up more. Penn State’s method for those who must: water at least 20 °F warmer than the egg and at least 90 °F, so the contents do not contract and pull the water in; one egg at a time, agitated rather than submerged, in water with a food-safe detergent; never scrub; rinse in water that contains an approved sanitiser and is slightly warmer than the wash water; dry the shell, then refrigerate promptly. Collecting, cleaning and storing duck eggs covers the whole routine from the nest onward, including keeping the ducks in until mid-morning so the eggs are laid indoors in the first place.

The float test

An egg loses water through its shell over time and the air cell at the blunt end grows. A fresh egg sinks and lies flat; an older one stands on end; an old one floats. That is all the float test measures: the size of the air cell, which is a proxy for age.

The USDA’s position is precise. A floating egg is an old egg; the test cannot say whether it is safe. Age and spoilage are different things — a fresh egg laid in a dirty nest can be contaminated, an old egg with an intact shell can be sound — and the float test cannot tell them apart. What the USDA does advise is cracking an egg into a separate bowl, never straight into the mix: an off smell or an unusual appearance means bin it. That check catches some bad eggs; it does not make any egg safe, and it never outranks the dates above.

Water glassing

The old method of storing eggs for months in a solution of sodium silicate has come back into fashion. Penn State’s verdict is “not recommended”, because of the risk of pathogens through the shell and because it is not reliably effective; the checker repeats that and we would apply it with more force to a duck egg, whose shell is more porous than a hen’s.

What this will not tell you

It will not tell you a duck-specific shelf life, because none is published — the duck egg’s thicker shell and larger air cell are often said to keep it longer than a hen’s, and that may be true, but nobody authoritative has put a number on it and we will not either. It will not tell you whether an egg is fertile or whether a broody has been sitting on it; an egg from a nest you did not know about is of unknown age and has been sat on, and the answer for that one is not to eat it. For what a duck egg is and how it cooks, duck eggs vs chicken eggs; for turning a recipe’s chicken eggs into duck eggs, the egg converter. If the eggs are for hatching rather than eating, the rules are different and the weight-loss tracker is the tool.