What Do Expiry Dates Mean? Two Different Labels Doing Different Jobs

A use by date is a safety instruction. It appears on foods that support the growth of dangerous bacteria without obvious signs, principally fresh meat, fish, dairy and ready meals, and eating the food after that date carries genuine risk that cannot be detected by looking or smelling, since the organisms that cause illness do not necessarily cause spoilage. In several jurisdictions selling food past its use by date is an offence, and freezing before the date extends it, since freezing halts microbial growth. A best before date is a quality statement. It indicates how long the manufacturer expects the food to remain at its best in flavour, texture and appearance, and food remains safe to eat afterwards, with the quality declining gradually rather than at a cliff edge. Dry goods, tinned food, pasta, rice and most preserved products carry this label. A sell by or display until date is neither of these and is stock control information for the retailer, which is why regulators in several countries have pushed to remove it from packaging entirely.

Date marks are determined by the manufacturer rather than by a regulator, following a defined process:

• •Shelf life testing, in which samples are stored under expected conditions and assessed over time for microbial growth, chemical change and sensory quality
• •Challenge testing for safety-critical products, deliberately introducing a target organism to establish whether the product supports its growth
• •Accelerated testing at elevated temperature for stable products, with models used to extrapolate to normal storage
• •A safety margin applied at the end, which is conservative because the liability for being wrong is severe and the cost of a shorter date falls mostly on the consumer
• •An assumed storage condition, which is why the date is meaningless if the chain was broken, and why a temperature stated on the packet is part of the instruction rather than advice
• •Once opened, the printed date usually no longer applies, which is why packets carry a separate instruction about consuming within a number of days

Date label confusion is one of the largest identified causes of avoidable household food waste. Surveys across several countries have consistently found that a majority of people cannot correctly distinguish the two labels and that a substantial proportion discard food solely because a best before date has passed. Estimates attribute a meaningful share of household food waste directly to date labels, and household waste is itself the largest segment of food waste in high-income countries, larger than losses in retail or manufacturing. The environmental arithmetic is significant, since discarded food represents the water, land, energy and emissions used to produce it, and food waste overall accounts for a share of global greenhouse gas emissions comparable to a large country. Retail practice compounds the problem, since stores remove stock well before dates to maintain appearance, and the historical prevalence of the meaningless display until date added a third number to an already confusing label.

Reform has moved in a consistent direction. Several major retailers have removed best before dates from fresh fruit and vegetables entirely, on the reasoning that people can judge whether a carrot is acceptable by looking at it and that the date does more harm than good. Regulators and industry bodies have issued guidance to standardise wording and to discourage additional dates. Campaigns have promoted simple household rules, principally that a use by date is a rule and a best before date is an opinion. Redistribution law has been adjusted in several places so that food past its best before date can legally be donated, which was previously blocked by cautious interpretation. Technology proposals include time and temperature indicators that change colour according to the actual thermal history of the package rather than displaying a fixed date, which would be more accurate and adds cost. The underlying tension remains that the manufacturer setting the date bears the risk of illness and not the cost of waste, which is an incentive structure that produces conservative dates.

A use by date is a safety limit on foods where dangerous bacteria can grow undetectably, and in several countries selling past it is an offence, while a best before date is a quality estimate after which food is still safe. Sell by dates are retailer stock control and are being removed. Manufacturers set the dates through shelf life and challenge testing plus a conservative margin, and surveys find most people cannot tell the labels apart, which drives a large share of household food waste.