Food spoilage

• Microorganisms- tiny living things found in air, water, soil, on people. They are mostly harmless but pathogenic ones can spoil food which can cause food poisoning
• Microorganism examples- bacteria, mould, yeast
• Microorganism conditions needed to grow and multiply-

  1. warm temperature
  2. plenty of moisture(water)
  3. plenty of food
  4. right pH(not too acidic or alkaline)
  5. enough time (eg. bacteria split every 10-20mins)
• Conditions to stop growth of microorganisms-

  1. use a fridge to change temperature
  2. pickle food in vinegar to change pH
  3. add salt(absorbs water to remove moisture)
• High risk foods- if not stored correctly could grow harmful bacteria
• High risk food eg-

  • cooked meat, fish, poultry
  • dairy products
  • gravies, stock, sauces
  • shellfish
  • cooked rice
• Enzymes- biological catalysts
• Enzymes- substances usually made from proteins that act as biological catalysts (speed up chemical reactions)
• Enzymes:

  • Ripening
  • Browning
• Ripening (Enzymes):

  1. Enzymes in fruit cause them to ripen which affects sweetness, colour and texture
  2. Eg. unripe bananas are green and firm but enzymes break down starch inside them to make them softer and sweeter
• Browning (Enzymes):

  1. When fruit sliced, oxygen in the air will turn fruit brown (oxidation). enzymes in fruit speed up this process
  2. Leaving some fruit to overripen will give them a brown colour
• Stop enzymes from working- adding acid

  • enzymes work best at certain pH so if add lemon juice to fruit, the acidic conditions will stop enzymic browning
• Slow down enzymes- blanching

  • blanching=plunging into boiling water for short period)
  • natural ripening enzymes will cause the veg to lose colour, texture, flavour and nutrients
  • Freezing will slow down enzymes
  • Blanching destroys ripening enzymes to veg retain colour...
• Mould (microorganism):

  • Spoil bread, cheese, fruit
  • Cause change in look, smell, taste
  • Causes a fuzzy appearance
  • Can cause food poisoning
• Yeast (microorganism):

  • commonly grow on surfaces of fruit eg. grapes, tomatoes
  • spoil by fermenting sugars by turning them into alcohol and carbon dioxide
• To preserve food, keep in right conditions so bacteria doesn't grow
• Cooking/Reheating-

  • Cook food above 75C (to kill bacteria)
  • reheat food properly and once
  • Reheat above 75C (check with temperature probe)
• Danger zone- 5-63C

  • because that is the temperature zone where bacteria grows
  • hot food held above 63C
  • optimum bacteria temp growth is 37C
• Chilling (0-5C)

  • slows down growth of bacteria
  • extends shelf life
  • causes harder texture
• Freezing (-18C)

  • stops bacteria growing as food becomes dormant
  • extends shelf life a lot
  • doesnt kill bacteria though as they become active when defrosts
• Fridge-

  • always kept between 0C and 5C
  • keep food covered or stored in containers
  • always store raw meat, poultry, fish on bottom shelf
  • keep cooked meat above raw meat
• Freezing-

  • Kept around -18C
  • Food should have clear labels with date they were frozen
  • Defrost meat and poultry in fridge
• Ambient foods- foods that stored safely at room temperature eg.bread, crips, canned food
• Ambient foods:

  • kept in seal containers too keep air out (keeps it fresh)
  • stored in dry, cool place (moisture helps bacteria grow)
  • methods of preservation- freeze drying, canning food, vacuum packing, using chemicals
• Use by date:

  • Shown on products with short shelf life eg. high risk foods
  • Given as safety warning
• Best before date:

  • for products with longer shelf life
  • if eat food after, its probably safe but not as nice
• Cross-contamination:

  Transfer of bacteria from raw to cooked food
• Cross contamination sources:

  • other contaminated food
  • utensils, equipment and work surfaces
  • people
  • pests
• Follow safety hygenine procedures- reduce risks of cross contamination
• Safety hygiene procedures-

  • Prepearing
  • Cooking
  • Serving
• Preparing:

  • wash hands
  • wear clean apron
  • wear hat or hair net
  • remove jewellery
  • cover cuts
  • separate raw and cooked food
  • using coloured chopping boards
  • wash raw vegetables
  • use clean equipment
• Cooking:

  • cook food at the right temperature
  • make sure food is cooked all the way through
  • use temperature probe to test the temperature
• Serving:

  • Serve food straight away or keep it above 63C for no longer than 2 hours
  • If serving food cold, cool it down within 90 minutes
  • keep food covered
• Food poisoning-

  • Caused by bacteria
  • Symptoms- sickness, diarrhoea, stomach cramps, fever
  • Get it by eating contaminated food containing contaminated pathogenic bacteria
• Main types of bacteria:

  • Campylobacter
  • E-coli
  • Salmonella
  • Listeria
  • Staphylococcus aureus
• Campylobacter (bacteria):

  • Most common cause of food poisoning in UK
  • found in raw or undercooked poultry or untreated milk/water
  • 2-5 days to feel symptoms
• Salmonella (bacteria):

  • Found in raw poultry, untreated eggs and milk
  • 6-72 hours to feel symptoms
• E-coli(bacteria):

  • live in intestines of animals
  • most harmless but some cause kidney damage and death
  • sources - raw beef, untreated milk/water, unwashed veg and salad leaves
  • 1-10 days to feel symptoms
• Listeria(bacteria):

  • found in soft cheeses, pate, shellfish
  • can grow in cold temperatures eg.fridge
  • pregnant women at higher risk
  • up to 70 days to feel symptoms
• S.aureus(bacteria):

  • live on skin, hair, in noses of animals and people
  • poor personal hygiene can contaminate food
  • 1-6 hours to feel symptoms