Microorganisms in Food Production (AQA GCSE Food Preparation & Nutrition)

The use of microorganisms in food production

• While microorganisms can cause food spoilage, there are some situations in which they are essential for food production, including:

  • mould in the production of blue cheese

  • yeast in bread-making

  • bacteria in yoghurt and cheese-making

Moulds in blue cheese

• Moulds are added to some cheeses during the production process to alter their texture, flavour and appearance, e.g. in:

  • Stilton

  • Gorgonzola

  • Roquefort

• The mould in blue cheese produces a creamy texture and a sharp, tangy flavour, and can often be seen as blue and green veining

• Note that the moulds used in blue cheese are chosen specifically for the purpose and do not cause harm when eaten

  • Other moulds would not work in the same way and may be harmful to consume

Martin Delisle, via Wikimedia Commons

Yeast in bread

• Yeast is used as a raising agent in bread as follows:

  1. yeast is mixed with flour and water and kneaded to form gluten and distribute the yeast evenly

     • Sugar may be added as an easy fuel for the yeast

  2. the yeast uses sugars for respiration, releasing carbon dioxide gas

  3. carbon dioxide forms bubbles that cause the dough to rise

     • This is known as proving, and requires warmth

  4. when baked the gas in the bubbles expands, causing the dough to rise further

Bacteria in yoghurt and cheese

• Particular types of bacteria are used in yoghurt production as follows:

  1. milk is boiled to kill any non-useful or harmful bacteria that may already be present

  2. useful bacteria are added to the milk

     • The bacteria are referred to as a starter culture

  3. the milk is gently heated to a temperature that is suitable for bacteria, which can then use the sugars present in the milk for respiration

     • this is known as fermentation

  4. the bacteria produce lactic acid, which denatures the proteins in the milk and causes the milk to coagulate

  5. the milk thickens and takes on a sour flavour; this is yoghurt

jules, via Flickr

• The cheese-making process begins in a very similar way to yoghurt, but contains some additional steps, including:

  1. once the milk has started to thicken, as described above, rennet enzyme is added

  2. rennet causes the milk to separate into liquid and solid components; the liquid is whey and the solids are curds

  3. the whey is removed and the curds are heated, pressed and salted to produce a solid block of cheese

     • Salt adds flavour and also acts as a preservative to prevent spoilage

  4. at this point the cheese may be left to mature for a period of time

• Note that specific types of bacteria are used in yoghurt and cheese making; these bacteria are not harmful and bring about the desired effect when added to milk

  • Contamination with harmful bacteria will cause the milk to spoil and may result in a harmful product