In most of food service facilities, food is not served just after cooking especially when preparing large quantities (such as party preparation or airport catering), also in restaurants and central kitchens of schools, hospitals, etc, some foods can be cooked or pre-cooked as to utilize out of peak periods or to manage the proper use of cooking equipments (equipments may not be adequate to cook all the food at the same time), then cooked food is kept refrigerated until serving time, then food is re-thermalized (re-heated) or finally cooked just before serving, which saves time in peak periods. Refrigerating of food after cooking can not be done by an ordinary refrigerator (e.g. reach-in refrigerator), where this type is designed to store cold food, that is already cold and not to cool hot food, in addition; providing of hot food inside a reach-in refrigerator or clod room may result in heating of surrounding cold foods inside the unit and accordingly will be damaged. One of the reasons for food borne illnesses is using of storage refrigerator to chill hot foods.
Hot food should be refrigerated in a blast chiller. Blast chiller is a refrigerator, with high cooling capacity, that can cool hot food quickly from 70 °C to 3 °C in a maximum period of 90 minutes (which can not be achieved by an ordinary refrigerator, see Fig.188.8.131.52).
Fig.184.108.40.206 Danger temperature zone
FOSTER REFRIGERATOR – UNITED KINGDOM
According to European and international healthy food regulations, food temperature has critical zone (or danger zone), which allow bacteria to rapidly growth. Critical zone is different according to different standards, but all ranges are around this range (68 °C to 8 °C). Simply, blast chiller allows food to quickly pass this zone to reduce time of bacteria growth (under ideal conditions, bacteria split into two every 20 minutes). In addition, blast chilling or rapid cooling decrease the percentage of food weight loss (less water is lost from food because of less refrigeration time), also rapid chilling stops forming of ‘ice skin’ which dehydrates and damages the product’s appearance especially for delicate food surfaces such as pasta and fruits, and finally does not allow change in food color, texture, nutritional value and flavor, which can be affected by slow refrigeration.
Blast chillers capacities are ranging from small, under counter units (Fig220.127.116.11) to cabinet or roll-in type up to modular type (Fig.18.104.22.168).
Fig.22.214.171.124 Under counter blast chiller
FOSTER REFRIGERATOR – UNITED KINGDOM
Fig.126.96.36.199 Modular type blast chiller
FOSTER REFRIGERATOR – UNITED KINGDOM
appearance especially for delicate food surfaces such as pasta and fruits, and finally does not allow change in food color, texture, nutritional value and flavor, which can be affected by slow refrigeration.
Blast chillers capacities are ranging from small, under counter units (Fig. 188.8.131.52) to cabinet or roll-in type up to modular type (Fig.184.108.40.206).
When food is frozen, the water content of the food is changed into ice in the form of ice crystals inside the food cells; big ice crystals can damage food cells affecting food texture. Quick or blast freezing results in smaller ice crystals (proportional relation; i.e. the quicker the freezing, the smaller the ice crystals), which means better food structure and appearance.
Blast freezer function is to freeze food from 70 °C to -18 °C in a maximum period of 240 minutes, or from 20 °C to -18 °C in a maximum period of 180 minutes.
Blast freezers are used for freezing of all types of foods; meats, poultry, fish, dough (see Bakery equipments, to know more about advantages of dough blast freezing), etc.
Blast freezer can be used as blast chiller with different food quantities (in kg) and different periods.
To feel the difference between a reach-in refrigerator or freezer and a blast chiller/freezer; for a reach-in refrigerator or freezer and a blast chiller/freezer of the same internal volume, the required electric power (mainly compressor consumption) for reach-in refrigerator ( 1 to 4) will be around 350 Watts (approx) and for reach-in freezer (-18 to -21) will be around 700 Watts approx, but for blast chiller/freezer it will be around 5 KW (approx).
Blast freezer or chiller temperature is controlled either by food probe(s) – (thermostat sensor inserted in food) – or by a timer. When the cycle is finished (temperature reached or time ended), an audible alarm will be activated.
Blast chillers and freezers have similar construction and features to reach-in refrigerators but with the following differences and additions:
- Blast chiller only or blast chiller/freezer
- Capacity; estimated in kg of chilled/ frozen food or in number of GN trays. The same equipment can be used for blast chilling of certain quantity in kg, and for blast freezing with less quantity.
- Should have hold facility; hold facility means that blast chiller or freezer acts as a reach-in refrigerator or freezer (storage unit) after reaching required temperature, to keep food at this temperature until unloaded. In large units, additional small condensing unit (compressor condenser) should be added for utilizing during storage process where no need for a large condensing unit, to avoid cycling & save large compressor power.
- Blast chillers/freezers can be provided with several days’ temperature/time record with or without printout.
- Electric controls; temperature probe(s) and/or timer, automatic defrost & re-evaporation, cooling process programs (see example), automatic changeability to storage cabinet after cycle is ended, temperature display, etc.
- See next example.
As shown in Fig.220.127.116.11, a modular Blast chiller/freezer with the following features; can work as a blast chiller or blast freezer, 150 kg chilling or freezing capacity (equipment is designed for occasional freezing; capacity stated is nominal and will be dependent upon product, type and density, loading, etc),
75 mm thick modular panels, robust white laminate exterior as standard or 304 grade stainless steel as an option, wall mounted refrigeration system leaves the floor clear for cleaning robust internal stainless steel bumper bars to prevent trolley damage, 2 different door opening widths available (700 mm and 900 mm) to suit all trolley requirements including combi-trolleys, floorless application for blast chilling, 25 mm built in floor available for blast freezing application, blast chilling from 90°C exceeding food safety requirements, Foster’s Circulair TM air circulation system ensures uniform chilling whilst protecting the food surface, temperature probe supplied as standard, 3 probe options also available, alarm sounds and unit switches to automatic hold (as a storage cold room) at end of cycle to keep the operator informed and food safe until it is needed, can be supplied with built in pressure release for added safety (MBCF models), HACCP software is available as an option in 3 formats for data retrieval and management, new control panel facilitates easier access for operation and servicing, operator-friendly fans cut-out whenever door is opened, suitable for changing to a cold room as a roll-through, giving complete temperature control for maximum efficiency and performance, easy program selection -menu driven dial lets the operator simply turn to select the required program, available programs are;
– Soft Chill; ideal for delicate product such as gateaux and patisserie items and high water content items such as vegetables, rice and pasta. By maintaining a higher air temperature, these delicate food products maintain their texture and appearance, with no dehydration or cell damage
– Hard Chill; general purpose chilling, ideal for standard chilling product such as cooked meat, pies, lasagne, individually portioned meals etc.
– Hard Chill Max; for high density or high fat content such as meat joints, portioned meals, stew, sous vide, etc.
– Shock Freeze; any product to be frozen can be shock frozen to -18ºC within 240 minutes
– Professional programs; 3 program options to be set up by the end user to suit their menu requirements, easy to set up for use whenever required
– Probe & Timed Chill/Freeze; All programs can be set to achieve temperature either on a timer or by use of a probe.
Unit dimensions are 1350 x 1300 x 2350 mm, maximum trolley dimensions 690 x 1040 x 1890, clear door opening 695 x 1898 mm, electric power supply 11.5 KW (3 Ph), model (MBC 150), manufactured by “Foster refrigerator” – United Kingdom. www.fosterrefrigerator.com