GCSE Food Technology (AQA) Food safety and hygiene
Food spoilage
Food spoilage Food products can t be stored for a long time without changes taking place. The changes that often occur are to the taste, texture and colour of the food. Microorganisms and enzymes cause food spoilage and can cause food poisoning. The three types of microorganism causing food spoilage are: 1. Bacteria 2. Yeasts 3. Moulds
- Microorganisms are all around us, in the soil and air, on animals and humans and on equipment and preparation surfaces in poor hygiene. - The problem is, these bacteria can t be seen without a microscope. However, a good thing about microorganisms are that the can be used in the food industry to produce products such as: Cheese Yoghurt Bread Quorn.
What conditions to bacteria need to grow? Temperature Bacteria grows rapidly at 37 degrees c, however, growth occurs between the temperature s 5 degrees c and 63 degrees c which is known as the danger zone. Food Foods containing large amounts of protein and water (High risk foods) are the best medium for bacterial growth. Time When in the right conditions, bacteria reproduce by dividing into two and this can occur every ten to twenty minutes meaning that within a few hours, one bacterium can become several million. Moisture Most foods contain moisture and so are ideal for maximum bacterial growth.
How does food poisoning happen? Food poisoning occurs if harmful microorganisms contaminate food and are allowed to grow. It s difficult to now if bacteria is present in foods as they don t actually affect the appearance, taste or even the smell of the food. Bacteria that cause food poisoning are called pathogenic bacteria. One example is clostridium botulinum. Pathogenic bacteria are very harmful and can cause death in young children and the elderly. Poor hygiene during the storage, preparation or serving of food can also result in food poisoning. The main types of food poisoning bacteria are: Salmonella This is the most common form of food poisoning in Britain. It s symptoms, such as diarrhoea, vomiting, head aches and stomach pains appear 12to 36 hours after consuming the affected food. Main sources of the bacteria are eggs and poultry. Campylobacter This has symptoms such as diarrhoea and headaches and these occur 1 to 11 days after eating the food. Main sources of the bacteria are meat, poultry and shellfish. Staphylococcus aureus This is a bacteria that creates toxins which causes the food poisoning. They are present in the nose, throat and skin of human beings and so can be transferred to foods by poor personal hygiene. The symptoms that appear one to six hours after consuming the food are vomiting, abdominal pain and diarrhoea. Main food sources are meat, poultry and salads.
How can we stop bacteria from growing in food? If we make changes to any of the optimum conditions needed by bacteria for growth it will stop them from reproducing or at least hopefully slow down the rate of reproduction. Temperature From looking at the thermometer it can be seen that: -18 degrees c Bacteria are dormant and are unable to reproduce. 0 to 5 degrees c Bacteria are sleeping and reproduce very slowly. 5 to 63 degrees c Bacteria produce most actively. This is known as the danger zone. 37 degrees c This is the optimum temperature for bacteria to reproduce. 72 degrees c The bacteria start to get destroyed and are unable to reproduce. Food Bacteria grow best on high risk foods (foods that have a high protein and water content). Time Food needs to be prepared as quickly as possible and should be chilled after preparation as it should not be allowed to wait around in danger zone temperatures before storing. Moisture Care must be taken when preparing food with a high moisture content.
How does preservation help ensure a longer shelf life If we change any of the optimum conditions that are needed by bacteria for growth then it will stop them from reproducing are greatly slow down the rate of reproduction.. The main methods of preservation are: Removal of liquid Drying, dehydration and jamming. Alteration of temperature Canning, freezing and chilling. Removal of air Modified atmospheric packaging. Addition of a preservative Jamming, Pickling and salting. Other substances are also able to cause food spoilage. Physical and chemical spoilage of foods can occur during storage, preparation and cooking. The main physical contaminants are jewellery, flakes of nail varnish, metal from equipment, hair and insects. Chemical contaminants are most likely to be cleaning fluids.
Food storage.
Food storage Freezing and chilling are the most popular ways of maximising the storage life of foods as the colour, taste, texture, flavour and nutritional value of the food is altered least of all the food preservation methods. These foods are readily available in the freezer and fridge sections of supermarkets.
Freezing and chilling food products Freezing food products preserves them for between 1 week and up to one year depending on the food. Most foods are able to be frozen quite easily; exceptions are those with a high water content, like strawberries and salad ingredients, or those with a colloidal structure, like sauces which may separate on thawing. Commercially frozen food is rapidly frozen using blast, plate or cryogenic freezing methods. This ensures that small ice crystals form in the food cells and that there is no damage to the structure of the food. If a food product is slow frozen then large ice crystals form which results in the food cell walls getting damaged. On thawing these foods have changes to their flavour, texture and nutritional values. Fast freezing involves reducing the core temperature of the food from 0 degrees c to -18 degrees c in 12 minutes. Freezing stops microorganisms from growing, it makes them dormant but it doesn t kill them. Domestic freezers are usually at a temperature of -18 degrees c but as commercial freezers are for longer-term storage they are kept at -29 degrees c.
Freezing and chilling food products continued Chilling doesn t preserve foods but it does extend it s shelf life for a few days. There is very little change to the taste, texture, flavour or nutritional value of these foods, in fact they are almost identical to fresh produce. Chilled foods are stored between 0 degrees c and 5 degrees c as this prevents the growth of Listeria monocytogenes, a common foodpoisoning bacteria. Foods that are going to be sold chilled are prepared using the cook chill method. This involves preparing and cooking the food and then it is blast chilled to a temperature of below 5 degrees c in 90 minutes. The foods must be stored at less than 4 degrees c for a maximum of 5 days. At home these foods are stored in the fridge. Modern lifestyles means that more consumers have less time to prepare food and therefore purchase foods that just need reheating.
Reheating foods There are some essential rules when reheating foods. They are: Ensure frozen foods are fully defrosted Follow the reheating instructions on commercially prepared food products All foods need to be reheated to a temperature above 72 degrees c Ensure that the core temperature of high risk foods and dense foods are at 72 degrees c by using a food probe. Here are instructions on how to use a temperature probe: 1. Plug in the probe 2. Make sure that it s clean (wipe using an antibacterial wipe) 3. Check that the digital reading is set to 0 4. Place into the centre of the food that needs to be tested 5. Hold it in place for 2 minutes 6. Make sure that the digital reading is static and take the reading 7. Remove from the food, read again 8. Clean it again using antibacterial wipes and reset the probe.
Food handling.
Food handling and personal hygiene. Everybody who works in the food industry needs to know and understand how food is produced safely. The key starting point is a high level of personal hygiene. What is good personal food hygiene? Wear clean protective clothing Tie hair back and cover with a hair net or hat Clean hands before touching food use antibacterial wash and hot water Cover all cuts with a blue waterproof dressing Keep finger nails short and clean without nail varnish Remove all jewellery Wear disposable gloves if possible where touching food Do not chew or smoke near food Don t touch your nose, ears or hair when handling food Report any illness to a supervisor e.g. Sickness, diarrhoea, cold or flu (this is a legal requirements).
What is good kitchen hygiene? Keep different food preparation areas for different foods, e.g. High risk fish and meat, medium risk vegetables and meat pies, low risk potatoes and jams. This prevents cross contamination The use of colour coded equipment to help prevent cross contamination This equipment must only be used for the specified foods and cleaned immediately after use Red raw meat Blue fish Green fruit and vegetables Yellow cooked meats Good facilities for cleaning and waste disposal Equipment and work areas kept in good condition, e.g. stainless steel sinks, regular removal of waste Methods for preventing insect contamination e.g. fly screens. What are the risks to food safety? When food is produced in a factory a production run occurs. There are chicks in place at each stage of the making of a product to make sure that the final product is of a good quality and is safe to eat. These check are called quality control checks and hazard checks.
Exam questions What are some rules that food workers should follow when working with food? (4 marks) Outline some methods of food preservation (8 marks)