Health Guidelines, Terms and Glossary:
Cook-Chill means a catering system based on the full cooking of food follow by fast chilling and storage in controlled low temperature conditions above freezing point (0°C to +3°C) and subsequent thorough reheating close to the consumer before consumption. It can take up to five days including the day of cooking but no longer as food quality diminishes (Department of Health, 1993).
Cook-Freeze means a catering system based on full cooking followed by fast freezing storage. At controlled low temperature conditions well below freezing point (-18°C or below) and subsequent thorough reheating close to the consumer before prompt consumption (Department of Health, 1993).
Microorganism growth is minimised when food is stored at a maintained temperature below freezing point (Department of Health, 1993).
Food Storage Temperature and Life
The recommended Cook-Freeze and long term storage temperature for food is -18°C. Food Cook-Chill food the storage life should not exceed 5 days with temperatures maintained below +3°C (Department of Health, 1993).
In Cook-Chill and Cook-Freeze operations initial cooking will ensure destruction of vegetative stages of any pathogenic microorganisms present. Rapid multiplication of pathogenic microorganisms occurs between 7°C and 60°C. Subsequently, this temperature range must be spanned as rapidly as possible to minimise growth during cooling, after cooking and during thawing or reheating (Department of Health, 1993).
Food Nutrient Retention
Nutrient content in food depends on the quality of the original raw materials, the storage conditions and the extent and nature of processing. Nutrient deficiency in vegetables increases proportionally to storage time before preparation and time held in water after preparation. Retention of nutrients and vitamins occurs if vegetables are cooked quickly and consumed as soon as possible afterwards. Reductions in nutrition can also be caused by over-cooking and prolonged delay between reheating and consumption; which can also cause loss of flavour and palatability. Cook-Chill processes can cause nutrient losses. However, fast chilling can stem the losses. Retention of nutrients in food can increase if products are stored below -18°C. Chemical Oxidation can also cause Nutrient deficiencies especially those with unsaturated fatty acid content (Department of Health, 1993).
Nutrient Content (quality of original raw materials)
Extent and nature of food processing
Nutrient and Vitamin C losses
Prolonged delays between reheating and consumption
Prolonged storages (especially vegetables)
Chemical Oxidation (exposure to oxygen/air)
Poor refrigeration processes
If vegetables are cooked quickly and consumed afterwards.
Storage below -18°C
Foods used as ingredients in meals, including those which have been pre-cooked (Department of Health, 1993).
Prepared food, i.e. food ready to be used for cooking, should be held at temperatures below +10°C until the cooking process commences (Department of Health, 1993).
The core temperature is the temperature of the central point of the food product. The time and temperature of the cooking should be sufficient to ensure that heat penetration to the centre of foods stuff will result in the destruction of non-sporing pathogens. This is normally achieved when the core temperature exceeds 70°C. To destroy Listeria monocytogenesthe temperature throughout the food should be held >70°C for >2 minutes.
Food portioning is dividing food into smaller quantities. After cooking food portioning should be completed in within 30 minutes for any product in a controlled environment room with the temperature <10°C (Department of Health, 1993).
Chilling Pre-Cooked Food
Chilling cooked food refers to the cooling process of cooked food to an overall temperature between 0°C and 3°C. Chilling should occur within 90 minutes of the product leaving the cooker. This helps preserve food appearance, texture, flavour, nutritional quality and safety of the cooked food (Department of Health, 1993).
Speed of chilling of a food stuff depends on:
Size, shape, weight of food and contruction material of the container;
Food density and moisture content;
Heat capacity of the food and the container;
Thermal conductivity of the food;
The design of the chiller;
Temperature of the food entering the chiller;
Whether the container is provided with a cover (Department of Health, 1993).
Pre-Chilled Food Storage
Chilled foods are much more vulnerable to temperature abuse during storage than frozen foods. There during storage it is important:
That the temperature of the cooked food after chilling be maintained below +3°C throughout the entire storage and distribution until reheating.
That the maximum storage life of chilled products does not exceed 5 days, including both the day of cooking and consumption. This also applies to where pre-cooked chilled products are purchased from outside suppliers.
Should the temperature of the cooked food in storage exceed +5°C, but not 10°C, and before reheating, the food should be consumed within 12 hours or destroyed.
Should the temperature exceed +10°C, during storage the chilled cooked food should be destroyed (Department of Health, 1993).
Freezing Pre-Cooked Food
Freezing should take placed <90minutes of the food leaving the cooker. The foods Core Temperature should reach -5°C within 90minutes of entering the freezing and subsequently reach a temperature of -18°C. Food that has thawed either partially or completely should not be re-frozen; and that which has thawed to an unknown temperature destroyed (Department of Health, 1993).
Cooked Frozen Food Shelf Life
Frozen food shelf life of cooked food varies with products but in general should not exceed 8 weeks. After the 8 weeks the food can lose nutrients and palatability, and rancidity can occur in high fat content products (Department of Health, 1993).
Food temperature measurement
No matter what device is used be it the electronic thermometers, PRT probes or infrared surface readers, the temperature of the food will not necessarily be the same as that of the surrounding air or cryogenic gas. Some temperature variations are likely to occur at different points in the processes. All records of temperatures and other monitoring results at critical control should be kept for at least three months. Indications of temperature abuse should be investigated and corrected promptly.
Variations in the total aerobic colony are the most useful guide to the hygiene and temperature control of the process. It is suggested by Department of Health (1993) that one sample of about 100 grams of each item of food be taken from each batch tested. Samples should be taken immediately before the food is due to be reheated so that the results reflect any abuse conditions to which the item sampled has been subjected during storage and transport following processing (Department of Health, 1993).
Food should generally achieve the following microbiological criteria:
Total aerobic colony count after incubation of agar plates for 48 hours at 37°C - <100,000 per gram.
Salmonella species – not detected in 25g.
Escherichia coli - <10/g
Staphylococcus aureus (coagulase positive) <100 per gram.
Clostridium perfringens <100/g
Listeria monocytogenes – not detected in 25g (Department of Health, 1993).
© Industrial Technologies Ltd 2017