The refrigeration of chilled foods 85 applications, and an appropriate choice must be made, dependent on the planned operation 4.7 Chilling equipment 4.7.1 Cooling systems For most prepared foods, air blast cooling chambers or tunnels are used. Water immersion(hydrocooling)is used for some vegetables, and for fresh, leafy produce, vacuum coolers may be appropriate. For some fresh produce which has relatively long storage life, cooling may be achieved using storage chambers, but frequently cooling rates will be enhanced by the use of special air circulation arrangements. Each of these systems will be considered in turn below 4.7.2 Blast chillers Blast chillers operate by passing cold air over foodstuffs at high speed. For cook-chill catering and similar operations, there are various guidelines, such as those issued by the dhss in the UK. These recommend that equipment should be capable of chilling foods of up to 50 mm thickness from 70oC down to a core temperature of 3C or below within 90 minutes. This requires an air speed of at least 4 metres per second and an air temperature of around -4oC Small,reach-in chillers taking batches of up to 30 kg are available, for buffer'supplies in catering and for teaching and research. Larger models with capacities of up to a quarter of a tonne of foodstuffs are designed to accommodate wheel-in trolleys of trays. a typical single trolley unit might have a nominal capacity of 45 kg, typically accommodated on a trolley taking 20 trays of food. The evaporator and fans are located to the side of the interior chamber and the compressor and condenser may be located either in the top of the unit or remotely, depending on whether the heat and noise emitted can be accommodated locally or not. Controls will permit the unit to be used as a chilled store at 0-3C, or will operate the chill ing cycle using any combination of air temperature, product probe temperature, or simple timer. At the end of the illing cycle, a defrosting cycle to remove ice and frost from the evaporator is operated. Total power draw for a 45 kg unit is about 7kw With a two-hour load/chill/defrost cycle, it is convenient to operate a four- batch shift, with the final batch being left in the cabinet as overnight storage Optionally, temperature recorders may be fitted to monitor operation. For larger units, there may be doors at each side, so that chilled trolleys may be rolled through into a chilled food holding store at 0-3.C. It is also possible to obtain combination units with a frozen food storage cabinet alongside a chiller/chill storage unit. This allows a caterer to remove frozen food, cook and portion it, then chill and finally store the completed portions Other forms of blast chillers have been developed for the chilling of fresh poultry, which use a carbon dioxide tunnel in which CO, snow is used to provideapplications, and an appropriate choice must be made, dependent on the planned operation. 4.7 Chilling equipment 4.7.1 Cooling systems For most prepared foods, air blast cooling chambers or tunnels are used. Water immersion (hydrocooling) is used for some vegetables; and for fresh, leafy produce, vacuum coolers may be appropriate. For some fresh produce which has a relatively long storage life, cooling may be achieved using storage chambers, but frequently cooling rates will be enhanced by the use of special air circulation arrangements. Each of these systems will be considered in turn below. 4.7.2 Blast chillers Blast chillers operate by passing cold air over foodstuffs at high speed. For cook-chill catering and similar operations, there are various guidelines, such as those issued by the DHSS in the UK. These recommend that equipment should be capable of chilling foods of up to 50 mm thickness from 70ºC down to a core temperature of 3ºC or below within 90 minutes. This requires an air speed of at least 4 metres per second and an air temperature of around
4ºC. Small, ‘reach-in’ chillers taking batches of up to 30 kg are available, for ‘buffer’ supplies in catering and for teaching and research. Larger models with capacities of up to a quarter of a tonne of foodstuffs are designed to accommodate wheel-in trolleys of trays. A typical single trolley unit might have a nominal capacity of 45 kg, typically accommodated on a trolley taking 20 trays of food. The evaporator and fans are located to the side of the interior chamber, and the compressor and condenser may be located either in the top of the unit or remotely, depending on whether the heat and noise emitted can be accommodated locally or not. Controls will permit the unit to be used as a chilled store at 0–3ºC, or will operate the chilling cycle using any combination of air temperature, product probe temperature, or simple timer. At the end of the chilling cycle, a defrosting cycle to remove ice and frost from the evaporator is operated. Total power draw for a 45 kg unit is about 7 kW. With a two-hour load/chill/defrost cycle, it is convenient to operate a four￾batch shift, with the final batch being left in the cabinet as overnight storage. Optionally, temperature recorders may be fitted to monitor operation. For larger units, there may be doors at each side, so that chilled trolleys may be rolled through into a chilled food holding store at 0–3ºC. It is also possible to obtain combination units with a frozen food storage cabinet alongside a chiller/chill storage unit. This allows a caterer to remove frozen food, cook and portion it, then chill and finally store the completed portions. Other forms of blast chillers have been developed for the chilling of fresh poultry, which use a carbon dioxide tunnel in which CO2 snow is used to provide The refrigeration of chilled foods 85