Commercial freezer temperature: why −18 °C is the number everyone uses

Where −18 °C comes from

The figure is simply 0 °F converted to Celsius. It became the working standard in the frozen food industry decades ago and was written into international guidance: the Codex Code of Practice for the Processing and Handling of Quick Frozen Foods uses −18 °C as the reference temperature for storage and distribution. FSSAI's Schedule 4 says frozen food should be received at −18 °C or below and its catering section repeats −18 °C or below for frozen storage.

The number is under review internationally. In 2025 the Codex food hygiene committee asked FAO and WHO for advice on the holding temperature, and WHO has noted that storage warmer than −18 °C may affect safety with respect to parasites as well as quality and shelf life. For now, −18 °C remains the figure to work to.

What freezing does and does not do

Pathogenic bacteria stop multiplying at temperatures well above −18 °C. Freezing does not kill most of them; it puts them on hold. When food thaws, they become active again, which is why thawed food must be handled like fresh perishable food.

So why go as cold as −18 °C? Because quality keeps changing at temperatures between about −5 °C and −15 °C. Enzymes stay slowly active, fats oxidise and turn rancid, and ice crystals grow, drawing moisture out of the cells. Colder storage slows all of that. −18 °C is a practical balance between quality, shelf life and the energy cost of going colder.

Freezer temperature bands and what they mean

Air temperature versus product temperature

A freezer's display shows air temperature at the sensor. During a defrost cycle, or just after the lid has been open, the air can read −10 °C or warmer while the frozen product, which holds its cold well, is still around −18 °C. That is why a single warm air reading is not the same as thawed food.

To know the product temperature, probe between two packs (sandwich the probe tip between them) or use a dedicated frozen-food probe. Don't drill into frozen product with a standard thermometer; you will damage the probe. If product readings are consistently above −15 °C, the freezer is not coping.

Keeping a deep freezer at −18 °C in a hot kitchen

• Site it away from ovens, fryers and direct sun. A chest freezer in a 42 °C store room works far harder than one in a ventilated space.
• Leave the clearance the manufacturer specifies around the condenser, and keep it free of dust and lint.
• Don't load large quantities of unfrozen food at once; a storage freezer is not a blast freezer and will warm the stock around it.
• Keep lids and doors shut. Chest freezers hold cold well because cold air sinks and stays in, but a lid left open still lets heat flood in.
• Defrost manual-defrost models before ice builds up; thick ice insulates the evaporator and cuts capacity.
• Protect the compressor from voltage sags and spikes; an appropriate stabiliser and a dedicated earthed socket help.

If the freezer warms up

Check whether the product is still frozen hard and how long it was warm. Food that still has ice crystals and has stayed cold can generally be kept frozen, though quality may suffer. Food that has fully thawed and sat above 5 °C needs a decision under your food-safety plan, not a guess. Record the event and get the freezer serviced before restocking.