Micro-organisms in food production

• What is the definition of pathogenic?

  A micro-organism that is harmful to humans and can cause food poisoning
• What is the definition of non-pathogenic?

  A micro-organism that is not harmful to humans and does not cause food poisoning
• What is the definition of pasteurisation?

  This means heating fresh milk to 72C for 15 seconds in order to kill pathogenic micro-organisms that may be in it
• What is the definition of homogenised?

  Forcing milk under high pressure through a fine sieve, in order to break up the fat into tiny droplets. This means that the droplets stay suspended in the milk and do not separate out into a layer of cream
• What types of micro-organisms are used in cheese production?

  Bacteria and moulds
• What is the role of moulds in blue cheeses?

  They give blue colour and distinctive flavour
• What type of cheese uses only bacteria in its production?

  Cheddar cheese
• What are the stages of cheese production?

  1. Pasteurisation of milk
  2. Addition of special bacteria culture
  3. Addition of rennet
  4. Cutting the curds
  5. Draining off the liquid whey
  6. Drying the curd
  7. Milking the curd
  8. Pressing the cheese
  9. Ripening/maturing the cheese
• What happens during the pasteurisation of milk?

  Milk is heated to 72°C for 15 seconds
• Why is pasteurisation important in cheese production?

  It kills pathogenic bacteria in the milk
• What does the special bacteria culture do to lactose sugar?

  It turns lactose into lactic acid
• What are the effects of lactic acid on cheese?

  It coagulates protein, adds flavour, preserves cheese
• What is the function of rennet in cheese production?

  It coagulates the protein in milk
• What are curds and whey?

  Curds are solid, whey is liquid
• Why are curds cut into small pieces?

  To help form the final texture of cheese
• What is done with the liquid whey after draining?

  It is used to make ricotta cheese
• Why is whey considered a valuable by-product?

  It contains high biological value protein
• What happens during the drying of curd?

  Curd is stacked to drain more whey
• What is the purpose of heating and milling the curd?

  To cut curd into small pieces for texture
• What role does salt play in cheese production?

  It adds flavour and helps preserve cheese
• What is the purpose of pressing the cheese?

  To form a solid block of cheese
• What is the ripening process in cheese production?

  It develops flavour, texture, and colour
• How long is cheese typically ripened?

  For a few weeks or months
• Why is cheese stored in a cool place during ripening?

  To control growth of moulds and bacteria
• How does the ripening time affect cheese flavour?

  Longer ripening develops stronger flavours
• Blue cheeses

  Blue cheeses such as Stilton, Gorgonzola and Danish Blue use special moulds to give them their distinctive blue pattern and flavour.

  Blue Stilton cheese is a very traditional English cheese and is made in a similar way to Cheddar cheese, except for a few differences.

  1. The spores of a special mould are added to the pasteurised milk with the bacteria culture in stage 2

  2. In stage 8, the curds are put into a cylinder-shaped mould for a while, but they are not pressed. They are taken out of the moulds and allowed to continue to drain during the ripening process in stage 9

  3. When the cheese has developed its traditional crust (rind), it is pierced with stainless steel needles to allow air into the cheese. This enables the mould spores to germinate and spread inside the cheese to form blue ‘veins’ and a distinctive flavour
• Moulds used in cheese making

  . Non-pathogenic (harmless) moulds are also used to ripen cheeses and add flavour to them

  . For example, in cheeses such as Brie and Camembert, special mould spores are either sprayed onto the cheese or is dipped into a liquid containing them

  . By carefully controlling how the cheese is stored while it is ripening (which only takes a few weeks), this type of cheese will develop a white surface mould, and a special flavour
• Micro-organisms used in the production of bread

  . When bread is made, a specially cultivated, non-pathogenic variety of micro-organism yeast is used

  . Yeast is a type of microscopic, single-celled fungi and is related to mushrooms

  . Specific types of yeast are produced for use in bread making

  . If given the right conditions of warmth, moisture, food (sugar or starch) and time, yeast will use the sugar or starch for energy and produce carbon dioxide (CO2) gas to make bread and other yeast doughs rise, and alcohol as by-products

  . This whole process is called fermentation
• What is yogurt made from?

  Milk fermented by non-pathogenic bacteria
• What are the steps in yogurt production?

  1. Preparing the milk

  • Heat treatment destroys pathogens
  • Homogenisation keeps fat droplets suspended
  • Optimal temperature for bacteria is 42°C

  1. Adding the bacteria culture

  • Milk held at 42°C for fermentation
  • pH reaches 4.5, then cooled to 7°C
  • Lactic acid denatures proteins, making milk semi-solid

  1. Flavouring the yogurt

  • Addition of fruit or other flavors
  • Variety of choices available
• What types of milk can be used to make yogurt?

  Whole, semi-skimmed, or skimmed milk
• Why is heat treatment important in yogurt production?

  It destroys pathogenic bacteria in the milk
• What is the purpose of homogenisation in yogurt production?

  To keep fat droplets suspended in the milk
• What temperature is optimal for bacteria growth in yogurt production?

  42°C
• What happens when the pH of the milk reaches 4.5?

  The milk is cooled to 7°C to stop fermentation
• What effect does lactic acid have on milk proteins?

  It denatures and coagulates the proteins
• What is the result of lactic acid production in yogurt?

  The milk becomes semi-solid
• What is the purpose of cooling the milk to 7°C?

  To stop the fermentation process
• What gives yogurt its distinct flavor?

  Lactic acid and other natural substances
• What types of flavors can be added to yogurt?

  Fruit, honey, coconut, fudge, ginger