guacamoleGuacamole – Serves 4
The avocado is protected from browning by tossing in lemon juice. Serve with pitta bread or tacos.

1 small tomato
1 large ripe avocado
juice of lime or lemon
½ small red onion finely chopped
optional – ½ small, finely chopped red chilli
salt and pepper
chopped coriander or chopped parsley to decorate


  1. Remove the skin from the tomato either by leaving in boiling water for 30 seconds or holding over a gas flame with the tomato spiked on a fork.
  2. Chop the tomato into very small pieces and put in a bowl.
  3. Cut the avocado in half, remove the stone, and scoop out the flesh into a bowl.
  4. With a fork, mix in the lime or lemon juice, onion, chilli if used and salt and pepper.
  5. Serve topped with chopped herbs and tortilla chips or pitta bread.

The science bit

When cells in fruit or vegetable are cut or damaged, they are exposed to oxygen in the air and change colour.
Enzymes catalyse this reaction – this means they speed it up.
Enzymic browning makes fruit and vegetables change colour.
Acid ingredients such as lemon juice prevent enzymic browning and stop fruits and vegetables changing colour.
The juice of the lime or lemon coats the pieces of avocado and stops the enzymic browning taking place so the avocado pieces do not turn brown.

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Filed under Food GCSE Recipes, Food science

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