Best before vs use by: what food dates actually mean

There are two completely different kinds of date printed on food, and most of us treat them as one. Best before is a quality promise: the maker's estimate of how long the food stays at its best. Use by is a safety limit on the small set of foods where invisible spoilage can genuinely make you ill. Learning to tell them apart is the single highest-value thing you can know about food dates.

Best before: a promise about quality

Best before — also printed as "best if used by" — means the manufacturer expects the product to be at full quality until that date. Crisps still crisp, biscuits still snapping, coffee still aromatic, tinned tomatoes still bright. After the date, the product is not dangerous. It is simply drifting away from the version the maker wanted you to taste.

Dry pasta a month past best-before is dry pasta. Sealed rice, sugar, salt, honey and vinegar are effectively indefinite; the date on those is closer to a formality than a forecast. Tinned food a year past its date is usually fine if the tin is not bulging, rusted or leaking. Where best-before really bites is subtler: nuts and cooking oils go rancid, spices fade to dust, and flour eventually turns. Those are quality failures too — you notice them by taste, not by illness.

Use by: a genuine limit

Use by appears on the foods where dangerous bacteria can multiply without changing the smell, taste or appearance in a way you would notice. Fresh meat and poultry, fish, ready meals, pre-cut salads, soft cheeses, fresh dairy in some countries. Here the date reflects laboratory testing on how long the product stays safe when stored as instructed.

The reason this category needs a date at all is precisely that your senses do not cover it. Sour milk warns you loudly. Listeria on a pre-packed salad does not. That asymmetry — not the food being fragile — is what use-by is for. When in doubt with these, the date wins over your nose. That is the one place where the printed number really is smarter than you are.

The Japanese pair, which is unusually clear

Japanese packaging draws this line more explicitly than most, and the two terms are worth knowing even if you never shop in Japan, because they name the concept so cleanly.

賞味期限 (shōmi kigen) is best-before — literally the "enjoy the taste" limit. It goes on food that keeps relatively well: snacks, instant noodles, tinned goods, seasonings, tofu, yoghurt. Past it, quality slowly declines; safety does not fall off a cliff.

消費期限 (shōhi kigen) is use-by — the "consume" limit. It appears on food that spoils quickly, generally within about five days: bento, fresh sandwiches, raw meat and fish, fresh cream cakes. Past it, do not eat it.

Two things follow from this that surprise people. Both dates assume the package is unopened and stored exactly as the label says. Once you open it, neither date applies any more — you are on the opened-food clock, which nobody printed. And on 賞味期限 items, the maker has usually built in a safety margin below the tested limit, which is part of why so much perfectly good food goes in the bin on the day it turns.

How to actually use this

• Check which of the two it is before you decide anything. The word matters far more than the number. This one habit prevents most avoidable waste.
• On best-before, promote your senses. The date is a prior; your nose, eyes and a small taste are the evidence. Evidence outranks a prior.
• On use-by, follow the date. Freezing before it, though, moves the goalposts legitimately — freeze on day three, and the clock stops.
• Note the day you opened things. Once the seal is broken, the opened-food clock is the only one running, and it is usually much shorter than the printed date suggests.
• Store where the label says. A date is a conditional statement. "Keep refrigerated" is part of the sentence, not advice attached to it.

None of this is about being scrupulous or virtuous. It is that "best before" and "use by" answer two different questions, and once you can see which question you are being asked, most of the daily fridge-door hesitation just goes away.