Food Hygiene - Temperature Control
Bacteria will grow rapidly in foods especially in the right temperature. Temperatures between 5C and 63C are called The Temperature Danger Zone and it is important that the time foods are kept in this zone is kept to a minimum. Outside of this zone bacteria either stop growing or grow very slowly (bacteria will not grow above 63C).
In order to prevent the growth of bacteria you simply have to maintain the appropriate temperature i.e. keep hot food hot (above 63C) and cold food cold (5C or below).
Bacteria are killed by heat and are the reason why food should be cooked to at least 70C in the centre of the food and for at least 3 minutes. Some bacteria have a built in defense system in order to withstand the heat. They form spores or release toxins when higher temperatures, are needed in order to fully destroy them. If spores are present temperatures of over 120C are required to kill them.
Meat and Poultry
It should go without saying that the larger the joint or carcass the longer it will take to cook, it is important that the correct temperature is maintained for sufficient time and not just warmed up, this is particularly important when cooking:
Large Joints of meat – these should be cut into smaller pieces where possible to ensure that correct temperature is reached throughout the meat.
Rolled Meat and burgers – bacteria is usually just present on the surface of the meat and therefore easily killed however, when rolled the bacteria is then distributed throughout the meat and can be more difficult for the heat to kill them.
Poultry – can carry a large amount of bacteria and are spread throughout the carcass, it is sensible practice to cook a bird and stuffing separately as stuffing inside the bird can prevent the inside from reaching the desired temperatures.
Soups and Stocks
It is regarded as bad practice to top up existing soups and stocks with fresh batches, it will only be a matter of time before the temperature enters the danger zone and becomes a feeding ground for bacteria. It is safer if you prepare soups and stocks in small portions and dispose of any leftovers at the end of the day.
Eggs
Salmonella has been found inside a small portion of eggs and as a safe guard eggs should be thoroughly cooked. It is recommended that you avoid dishes that use uncooked or lightly cooked eggs, an example of this might be homemade mayonnaise. Pasteurised powered or liquid eggs should be used as a substitute.
Using a temperature food probe is an effective and cheap way of ensuring you have reached the correct temperatures with all of the foods mentioned. These should be recorded at regular intervals.
Hot Foods Hot
Eating high risk foods once they have reached the appropriate temperature following cooking are safe, however if there is a time lapse between cooking and serving then it is possible for the temperature to fall into the danger zone. If the delay is intended it is important that the appropriate equipment should be used to ensure that the foods are kept at a safe temperature level of atleast 63C. An example of this equipment might be a hot cupboard or bain marie. It is important that this equipment should already be at the correct temperature and that food should already be fully cooled before this equipment is fully used. This type of equipment should not be used to reheat food.
Cold Foods Cold
Cold food should be kept at the appropriate temperature until the nearest possible time until consumption and kept away from other foods. They should be handled as infrequently as possible to prevent the spread of bacteria onto them. Cold foods should always be kept covered.
Chilling and Reheating Foods
If you do not intend to serve food immediately then it should be cooled down appropriately. As guidance this should be below 10C within 90 minutes and then placed in the fridge. It is important not to put the hot food straight in the fridge as this will increase the temperature of the chiller unit.
Speeding up the process of chilling food can be assisted in a number of ways:
- Measuring the food into smaller portions
- Placing into a cold dish which is then immersed by iced water
- Allowing food to cool in chilliest part of the kitchen (ensuring that there is no risk of cross contamination
The re-heating of foods is the cause of most cases of food poising (mainly meat and poultry). It is often assumed that simply warming up the food will be sufficient as food has already been cooked once. The risk of food poisoning has increased as the food has to pass through the Temperature Danger Zone again. Using a food probe is recommended.
Spore forming bacteria may not have been killed in the cooking process and by only warming the food up you provide excellent conditions in which bacteria can multiply.
Guidelines for reheating food:
- Keep the food chilled as much as possible until reheating commences
- Keep food covered and clear of other foods
- Divide into smaller portions
- Heat to at least 70C for at least 2 minutes
- Do not reheat more than once
Refrigeration
You are breaking the law if your fridge temperatures reach higher than 8C. Commercial fridges should operate between 1C – 4C and it is these temperatures you should be recording each day.
By putting food into the fridge you do not kill bacteria but simply remove the warm temperatures bacteria need to grow and instead become dormant until the temperature increases again. However some food poisoning bacteria, such as Listeria, can grow slowly in a fridge.
Keeping foods refrigerated is a short term method and most foods fall in the 1 – 5 days however this does vary. Full information can be found on the manufacturers labelling and should not be stored past its use by date. Remember, it is against the law to sell foods that are unfit for human consumption.
Guidelines for refrigeration
- Keep raw meat and poultry away from other foods
- Ensure that nothing (particularly raw meats) can drip onto food below
- Allow cooked food to cool before placing in the fridge
- Keep all foods covered as much as possible
- Do not overcrowd the fridge
- Carry out regular temperature checks
- Minimise the amount of times the doors are opened and closed
- Defrost on a regular basis
Freezing
Freezers keep food at a temperature of between -18C to -25C and deny bacteria all warmth needed for them to grow and moisture into ice which prevents the bacteria from multiplying. Some bacteria will die as a result however some will just remain dormant and will once again grow should temperatures increase.
The length of time food can be frozen for depends on the type of food and the rating of your freezer. A guideline of between 2- 12 months, keeping food longer than manufacturer guidelines may not result in contamination but could result in deterioration of quality.
Guidelines for Freezing
- The freezer should lower the temperature of the food to -22C (the temperature should never rise above -18C)
- Wrap, label and date all food
- Store food neatly within the freezer and do not overload past the load line.
- Use old stock before new – know maximum storage periods
Thawing Food
It is not always necessary to thaw some foods before cooking however with others it is essential and you should always follow manufacturer’s guidelines.
There are a number of methods that can be used in order to thaw foods safely. Placing foods into containers and then into the fridge is best practice, although they will take longer to defrost. Planning is essential. For small meats and poultry defrosting can take place on the lower shelf in a container. Some microwave ovens also have a defrosting facility although it is important that manufacturer’s guidelines are followed at all times.
In order to determine the real temperature of food it is recommended to use a temperature probe. Care should be taken to keep these clean so they do not become a vehicle for cross contamination and regular calibration to ensure they are displaying an accurate temperature.
Fridge and freezer temperatures should be taken at regular periods, generally on each shift and recorded.
Cook-chill and cook-freeze
Cook-chill is the process of cooking the food and then rapidly cooling it down in 90 minutes (usually with a blast chiller) minimising the time bacteria is allowed to grow.
Guidelines on cook-chill food
- Use by date should be adhered to normally with 5 days inclusive of preparation and consumption
- Chilled food that rises above 10C during storage should be discarded
- Between 5C and 10C then food should be consumed with 12 hours
- Food must be taken from the chill no more that 30 minutes prior to reheating or to the food being eaten cold
- Reheating should take place immediately before food is due to be eaten
Cook Freeze is a similar process except that the cooked foods temperature is taken to at least -18C and then stored at that temperature until required (from between 2 – 12 months)
The same reheating and serving guidelines apply to cook freeze as they do to cook chill.
Microwaves
It is important to note that domestic microwaves (along with other domestic kitchen equipment) are not suitable within a commercial premise and are not designed to cope with the high volume of usage.
If you are using microwaves it is important that the desired temperature (70C) is reached throughout the food and that no cold spots exist (areas where the temperature is considerably colder) as bacteria will still exist. It is for this reason many microwaves have turntables so that the likelihood of cold spots are reduced.
Once food has been removed from the microwave the cooking process is still not over and standing time should be given to allow the heat to spread throughout the food and cook thoroughly.
Dry food storage
Your dry store should be cool, dry, clean and ventilated, an example of foods stored in these conditions would be; rice, flour, canned goods etc.
All food should be stored on shelves and kept off the floor at all times to minimise the risk of pests and contamination. Most dry foods have a long shelf life but you should always read the manufacturer’s instructions.
Food poisoning from canned foods is rare, however should the can show visible signs of rusting or burst at either end then they should be disposed of.
All food should be kept covered and/or contained at all times and checked that they are in the stated use by before use.
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