Chapter 5

• What conditions are needed for micro organisms to grow and multiply quickly?

  1. right temperature
  2. enough moisture
  3. food to eat
  4. time to grow
  5. right amount of acid or alkali
• Why can microbes grow and multiply in fridge but not freezer?

  If food is cooled to low temperature (0-5 degrees in fridge) microbes will still grow and multiply just very slowly. Whereas in a freezer it’s so cold (-18 degrees) the microbes become dormant (inactive) but are still alive
• Removing moisture from food will kill many microbes
• Some microbes are killed by acids eg. Vinegar in pickles, high levels of salt eg. Dried salted fish
• Why do micro organisms make food unsafe to eat?

  1. they put waste products and poisons into food
  2. large numbers of microbes in a food can make people ill because they irritate the digestive system
  3. not all microbes are unsafe eg. some are needed for food production, like yoghurt making
• what do enzymes do to food?

  1. ripen fruits and vegetables
  2. make unripe fruits change colour and become softer, juicer and sweeter
  3. break down the tissues of dead animals and fish
• What makes enzymes work

  1. right temperature
  2. oxygen from air
  3. right level of acidity
• What prevents enzymes from working?

  1. cooking
  2. mixing with air
  3. adding acids (lemon juice)
• How can enzymes make food unfit to eat

  1. fruits and vegetables become overripe making them soft and mushy. Overripe food go mouldy quickly
  2. some fruits and vegetables become discoloured when cut and open to air, they are safe to eat just not appetising
• What do moulds do to food to make it unsafe and unfit to eat?

  1. moulds send tiny spores which land on surfaces of food
  2. if conditions are right, spores germinate and send down roots into the food and you can see the mould growing on the surface of food
  3. the waste products from mould go into the food and can cause food poisoning
• What makes mould grow and multiply?

  1. warm temperatures
  2. moisture
  3. food
  4. right amount of acidity
  5. time
• Moulds will grow where there is a lot of moisture, eg inside an air tight plastic food box or a poorly ventilated cupboard (no fresh air)
• What does yeast do to make food unsafe and unfit to eat?

  they ferment (break down) sugars into CO2 gas and alcohol. Lots of pale brown spots will appear on food, fermentation by yeasts can happen in processed foods such as fruit and yogurts
• what makes yeast grow and multiply

  1. sugars in food
  2. temperature (ideally 25 - 37 degrees)
  3. moisture
  4. time
• Yeast multiply by budding
• How is yeast used for bread making?

  1. fresh, dried, fast-acting dried yeast
  2. yeast needs warmth, moisture, starch/sugar and time to ferment the starch and sugar to CO2 gas and alcohol
• How is bacteria and moulds used in cheese making?

  1. the bacteria used is specially produced in large amounts called a culture
  2. moulds used are specially produced in controlled conditions
  3. milk is pasteurised to kill pathogenic bacteria
  4. bacteria culture added to milk turns lactose in the milk into lactic acid
  5. lactic acid adds flavour, texture, preserves cheese
  6. rennet added - turns milk to curds and whey
  7. whey drained off
  8. curds cut up, salt added, then curds are pressed
  9. bacteria ripen the cheese to develop flavour
  10. cheese left to mature for a few weeks
• How is bacteria used in yoghurt making?

  1. special bacteria culture added to pasteurised and homogenised milk
  2. milk held at 42 degrees to let bacteria ferment the lactose sugar to lactic acid
  3. milk becomes semi-solid due to coagulation of protein by lactic acid
  4. milk cooled - flavouring may be added
• What are the symptoms of food poisoning?

  1. bad stomach ache
  2. diarrhoea
  3. feeling sick (nausea)
  4. being sick (vomiting)
  5. headache
  6. dizziness
  7. high body temperature
  8. feeling cold and shivery
• A person with food poisoning is unlikely to have all food poisoning symptoms, different types of bacteria cause different symptoms. A person can start to feel ill after a few hours or a few days. They may be ill for several days
• Why does bacteria cause food poisoning?

  1. most bacteria cause it inside the digestive system
  2. some bacteria get into bloodstream and go round the body causing damage to body organs, eg. Liver and kidneys
• What are the most common bacterias?

  1. campylobacter
  2. escherichia
  3. salmonella
  4. listeria
  5. staphylococcus aureus (S.Aureus)
• Which food is campylobacter found in?

  Raw poultry, meat, milk, dirty water
• What food is found in escherichia coli?

  Meat, minced beef, untreated milk, dirty water
• What food is found in salmonella

  Raw and undercooked poultry, eggs and meat, untreated raw milk
• What food is found in listeria

  Soft cheese, cheeses made from untreated raw milk salads pates
• What food is found in staphylococcus aureus?

  Untreated milk, cold cooked meats, dairy foods
• What is the danger zone?

  5 - 63 degrees
• If conditions are not right bacteria produce spores, they stay inside the spore and when conditions are right they germinate. If bacteria spores germinate, they produce very strong and dangerous poisons (toxins) which can cause serious illness and even death
• How to use temperature probe?

  1. reset probe before use
  2. Sterilise before use with antibacterial wipe
  3. The probe into the core/thickest part of the food
  4. Don’t touch the metal baking tin or pan base with the tip of the probe
  5. Leave the probe in place until the temperature stabilises
  6. Temperature must reach 75° or above
  7. The temperature must remain at 75° or more for at least two minutes
  8. Sterilise the food probe after use within antibacterial wipe