Food Spoilage (AQA GCSE Food Preparation & Nutrition): Revision Note

The signs of food spoilage

• Food spoilage can occur due to the action of:

  • enzymes

  • microorganisms, such as:

    • mould

    • yeast

    • bacteria

Signs of food spoilage due to enzymic action

• Sliced fruit may turn brown due to oxidation on exposure to air; this is known as enzymic browning, e.g.

  • apples

  • pears

• Enzyme activity can result in fruits becoming overripe, e.g.

  • bananas

  • avocado

Jason Thibault, via Flickr

Signs of food spoilage due to mould growth

• Moulds are fungi that spread by the growth of thread-like filaments; moulds can grow in conditions that include:

  • acid or alkaline

  • high sugar

  • high salt

  • moist or quite dry (e.g. on hard cheeses)

  • warm temperatures

• Moulds often grow on foods such as:

  • bread

  • cheese

  • jam

  • fruit

• Visible mould can be green, black or white in colour and may have a furry appearance

• Mould that is visible on the surface of food is a sign that microscopic moulds are present within the food

NotFromUtrecht, via Wikimedia Commons

Signs of food spoilage due to yeast

• Yeasts are single-celled fungi; growth conditions include:

  • either in the presence or absence of oxygen

  • high enough moisture levels

  • warm temperatures

• Yeasts often grow on or in acidic, sweet foods such as:

  • fruit, e.g. grapes, strawberries and tomatoes

  • fruit juice, e.g. orange juice

  • honey

  • jam

  • sweetened yoghurt

• Yeasts that grow in the absence of oxygen can ferment the sugars in food; signs of this include:

  • gas bubbles that contain carbon dioxide forming on the surface of liquids

  • an alcoholic taste

  • a slightly fizzy mouthfeel