A blast chiller works by blowing very cold air hard across hot food, pulling the heat out far faster than a fridge can. Foster rates its cabinets to take food from +70°C to +3°C in 90 minutes, or to -18°C in under 240 minutes in freeze mode. A soft chill keeps the air at +2°C for delicate food, while a hard chill runs the air down to -15°C first for dense dishes.
This guide explains what goes on inside the cabinet, what the different cycles do, how to load it so it actually hits its time, and how it differs from the fridge it is often confused with. The figures come from Foster's blast chiller manuals, UK food hygiene guidance and the regulation that defines a blast cabinet.
At a glance
| Question | Short answer |
|---|---|
| What it does | Rapidly cools hot cooked food, rather than storing cold food |
| Typical chill | +70°C to +3°C in 90 minutes (Foster's rating) |
| Typical freeze | +70°C to -18°C in under 240 minutes (Foster's rating) |
| Soft chill | Air and food kept at or above +2°C, for delicate food |
| Hard chill | Air down to -15°C for most of the cycle, then +2°C, for dense food |
| How it knows when to stop | By a core probe in the food, or by a set time |
| Afterwards | Holds at about +2°C until you move the food to storage |
What a blast chiller is
UK law has a definition. Commission Regulation (EU) 2015/1095, retained in UK law, describes a blast cabinet as an insulated refrigerating appliance "primarily intended to rapidly cool hot foodstuffs to below 10 °C in the case of chilling and below -18 °C in the case of freezing". Its capacity is defined as the food weight it can process to those temperatures in a single operation, which is why blast chillers are sold by kilograms per cycle rather than by litres.
That definition is the key difference from a fridge. A refrigerated storage cabinet is built to hold food that is already cold at a steady temperature. A blast chiller is built to take heat out of hot food quickly, and then hand it over to storage.
How a blast chiller works
Inside, a blast chiller has the same basic parts as any refrigerator: a compressor, an evaporator coil, a condenser and fans. What is different is the balance. The refrigeration system and fans are sized to remove heat quickly from a hot load, and the air is driven across the food so that the cold reaches every tray. Foster describes its Circulair air circulation system as ensuring uniform chilling while protecting the food surface.
The speed comes from moving air. Still cold air around a hot tray warms up and insulates the food. Fast-moving cold air keeps stripping that warm layer away, so heat leaves the food much faster. That is also why a blast chiller works much harder than a fridge while a cycle is running.
Most cabinets also have a core probe: a temperature probe pushed into the thickest part of the food. The controller reads it throughout the cycle and can end the cycle when the core reaches its target, rather than relying on a timer.
Soft chill and hard chill
Foster's service manual for its QC 11 and QC 600 blast chillers sets out the two main cycles clearly.
| Cycle | What the air does | What it is for |
|---|---|---|
| Soft chill | Brings food to +3°C in no more than 90 minutes without the air or food going below +2°C | Delicate food such as vegetables, rice, pasta, custard and fruit, where it prevents large ice crystals and keeps texture and appearance |
| Hard chill | Air drops to -15°C for the first part of the cycle to extract heat quickly, then rises to +2°C for the end to limit surface damage | Denser food such as meat pies, lasagne, pasta and individually portioned meals |
On the timed hard chill, Foster says the air runs at -15°C for the first 70 minutes and +2°C for the final 30 minutes. On the probe-controlled version, the split is the first 70% and the final 30% of the cycle. The guide to blast chilling in Foster's newer BCT manual suggests hard chill for meat, prepared dishes such as stews and lasagne, cakes and pastries, and soft chill for fish, vegetables, rice, potatoes, stewed fruit and fruit-based desserts.
Probe or timed cycles
A timed cycle runs for a set period. A probe cycle runs until the core probe reports that the food has reached its target. The probe is the more reliable choice, because it measures the food itself rather than assuming the load matches the setting. Foster's BCT manual says to clean and sanitise the fitted core probe before each use, and to check the food with a hand-held probe before and after, recording the result.
Hold mode after the cycle
When the cycle ends, either because the time has run out or the core temperature has been reached, Foster's QC manual says the controller switches to a hold mode and sounds an alarm. After a chill, it holds the air at about +2°C, and after a freeze, at about -21°C. Foster describes hold mode as a temporary storage facility until the food can be moved to proper storage.
That matters because a blast chiller used as a store is not available for the next hot batch. Once the cycle is done, move the food into a fridge or cold room that holds it at the right temperature.
How long a blast chiller takes
Foster's blast chilling range guide rates its cabinets to "Blast chill from +70°C to +3°C in 90mins with an entry temperature of up to 90°C" and to "Blast freeze from +70°C to -18°C in less than 240mins". Foster's QC manual says Department of Health guidelines set that target, +70°C to +3°C in 90 minutes, for blast chilling cooked food.
Those are ratings for a properly loaded cabinet. In practice, the time depends on what you put in. Foster's BCT manual notes that density, water content and fat content all change the time needed, and that a 10 kg meat joint will not chill like 10 kg of patisserie.
Loading a blast chiller properly
Most blast chillers that miss their time are being loaded wrongly rather than failing. Foster's BCT manual gives these rules:
- Keep food shallow. Do not overfill containers. Foster recommends a depth of 25 mm and a maximum of 3.75 kg per 1/1 gastronorm container.
- Leave lids off. Covers and lids extend the chilling time, and so do deep containers.
- Let the air through. Spread the load evenly over the shelves within the cabinet's rated capacity, and make sure air can circulate around the food.
- Do not overload. An overloaded cabinet will not reach temperature in time.
- Portion large joints. Large joints will not chill within the standard guidelines, so portion them first.
- Decant liquids. Put hot liquids into manageable gastronorm containers.
- Pre-chill the cabinet. Foster recommends pre-chilling to improve cooling time, and its guidelines suggest resting food for 30 minutes before blast chilling.
Why blast chilling matters for food safety
GOV.UK's food hygiene guidance for businesses says hot food must be kept at or above 63°C if it is not served straight away. It can be kept below 63°C for up to 2 hours, and after that it must be cooled as quickly as possible to 8°C or below, or thrown away. Its chilling guidance adds that chilled food must be kept at 8°C or below, which is a legal requirement in England, Wales and Northern Ireland and recommended in Scotland.
A blast chiller is the tool that does the "as quickly as possible" part reliably, and it produces the cycle records that show you did. Putting hot food straight into a fridge or cold room does the opposite: the food cools slowly and the rest of the stock warms up around it. Our guide to the cook chill process covers where the blast chiller fits in a production kitchen.
Blast chiller or fridge
| Blast chiller | Fridge or cold room | |
|---|---|---|
| Job | Remove heat from hot food quickly | Hold cold food at a steady temperature |
| Rated by | Kilograms per cycle | Storage volume |
| Air | Fast, and below freezing during a hard chill | Gentle, around the set point |
| Control | Cycle by time or core probe | Thermostat around a set point |
| Hot food | Designed for it | Not designed for it |
Standards and specifications
Blast cabinets for professional kitchens are tested under BS EN ISO 22042:2021, which BSI describes as specifying requirements for verifying the performance and energy consumption of blast cabinets used in commercial kitchens, hospitals, canteens and institutional catering, up to a load capacity of 300 kg. When comparing models, compare the rated capacity per cycle and the conditions it was rated under, rather than the shelf count. Our guide to blast chiller costs covers what drives the price.
Keeping a blast chiller on its cycle time
- Ventilation. Foster's BCT manual asks for at least 150 mm of clearance around the cabinet for ventilation.
- Condenser. A dirty condenser does not usually stop a blast chiller outright. It slowly stretches the cycle until it no longer meets its rated time.
- Probe. A damaged or inaccurate core probe can end cycles early or late, so check it against a hand-held probe.
- Records. If cycle times are creeping up with the same loads, that is the time to have it serviced.
Our blast chiller service covers repairs and maintenance across London, and planned refrigeration maintenance keeps condensers and probes checked on a schedule.
Questions people ask about blast chillers
How does a blast chiller work?
It blows very cold air quickly across hot food so heat is drawn out much faster than in a fridge. A core probe in the food tells the controller when the target temperature has been reached, and the cabinet then holds the food cold until it is moved to storage.
How long does a blast chiller take?
Foster rates its cabinets to chill from +70°C to +3°C in 90 minutes and to freeze from +70°C to -18°C in under 240 minutes. Real times depend on the food, the depth of the trays and how full the cabinet is.
What is the difference between soft and hard chill?
Soft chill keeps the air and food at or above +2°C, for delicate food like vegetables, rice and custard. Hard chill drops the air to -15°C for most of the cycle, then raises it to +2°C, for dense food like lasagne and meat pies.
What temperature does a blast chiller go down to?
In a hard chill, Foster's QC cabinets run the air down to -15°C. In freeze mode, the target is -18°C in the food, and in hold mode after freezing, the air is kept at about -21°C.
Can I store food in a blast chiller?
Only for a short time. Foster describes hold mode as temporary storage until the food can be moved to a proper store. Using it as a fridge means it is not free for the next hot batch.
Can I put hot food straight into a blast chiller?
Yes, that is what it is for. Foster rates its range for an entry temperature of up to 90°C, though its guidelines suggest resting food for 30 minutes first, and the cabinet works best pre-chilled.
The short version
A blast chiller is a heat extractor, not a fridge: fast cold air, a probe in the food and a cycle that ends when the core is cold. Load it shallow and uncovered, pick soft or hard chill to suit the food, move the food to storage when the cycle ends, and keep the condenser clean so it keeps meeting its time.
Last updated: 4 November 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.