Category Archives: Food science

Mayonnaise


Mayonnaise
This can take 5-10 minutes to make. You must go slowly when adding the oil.
The egg and oil need to be at room temperature.

Ingredients
1 egg yolk – at room temperature
pinch of salt
pinch of mustard powder
pinch of finely ground pepper
200ml vegetable oil – you can use a little olive oil for flavour
1 teaspoon white wine vinegar

Method

  1. Separate the yolk from the white. Use the white for meringues or an experiment.
  2. Put the egg yolk in a large, clean bowl. Stand the bowl on a damp dishcloth to stop it from slipping.
  3. Add the salt, mustard and pepper and whisk with a balloon whisk to make it thick and sticky so it is ready to take in the oil.
  4. Slowly – a ½ teaspoon at a time – whisk in the oil. Take time over this as you need to get the oil and egg to blend together. This takes a few minutes and the egg yolk and oil mixture begins to thicken and emulsify. Once the emulsification process has happened the oil can be added easily.
  5. Add more of the oil slowly – if the mixture gets too thick add a little warm water.
  6. Stir in vinegar and taste. Add seasoning if needed. Store in the fridge and use within 3-5 days.

The science bit

Egg yolks contain emulsifying agents including lecithin which form an emulsion where one liquid is dispersed in another.
Mayonnaise is an oil in water emulsion made from egg yolk, seasoning and oil.
The liquid in the egg holds the oil in an emulsion – just like emulsion paint.
If the recipe curdles, the oil has not mixed with the egg and the mixture separates.
The colour of the mayonnaise turns from yellow to cream as the mixture emulsifies.
The salt helps to thicken the yolk and the mustard helps with emulsification.

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Fish cakes with tartar sauce


 

Fish cakes with Tartar sauce – makes 2
These salmon fishcakes are served with home made tartar sauce which is made from mayonnaise and gherkins.

Ingredients
125g portion of salmon lightly cooked in a little milk
150g cooked, mashed potato
Salt and pepper
chopped chives or finely sliced spring onion
Flour for dusting
1 egg, beaten
some breadcrumbs or finely crushed plain crisps.
2 tablespoons oil

Method

  1. Mash together the fish, potatoes, salt and pepper and stir in the chives or spring onions.
  2. Shape into 2 equal sized fish cakes. Use the flour on your hands to stop sticking.
  3. Brush each fish cake in beaten egg and then coat with breadcrumbs or crushed crisps
  4. Fry in hot oil for 5 minutes on each side until crisp and golden.

Tartar sauce
Ingredients
2 tablespoons home made or bought mayonnaise
1 gherkin (30g) finely chopped
1 teaspoon capers finely chopped (5g)
finely chopped chives or parsley

Method
Stir all the ingredients together and taste. Add seasoning if needed.

The science bit

Egg yolk in mayonnaise is partly denatured by the whisking.
Egg yolk contains a fat called lecithin, an emulsifying agent, and as the oil is whisked in, the emulsion starts to form.
The protein molecules uncoil and surround the oil droplets.

 

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Quiche


Quiche – Serves 6
Use ready-made pastry for this dish to save time. Mary Berry does it!
Replace bacon with vegetables such as courgettes or broccoli florets.

Ingredients
Pastry
175g plain flour
100g butter or margarine
Water to mix
Filling
100g bacon cut into pieces – optional
100g grated cheese
3 eggs
150ml milk
pepper

Method

  1. Preheat the oven 200°C/Gas 6.
  2. Rub the butter into the flour until it looks like breadcrumbs and add enough water to make a firm dough.
  3. Line a 20 cm diameter flan tin with pastry, fill with baking paper and baking beans and bake blind for 15 minutes. Remove beans and paper and bake for another 5 minutes.
  4. Turn down the oven to 160°C/Gas 3.
  5. Fry the bacon until crisp. Place the bacon and 75g cheese in the flan case.
  6. Beat eggs and milk and season. Strain over the bacon and cheese. Top with the rest of the cheese.
  7. Bake for 35 – 40 minutes until the filling is set. Serve hot or cold.

The science bit

If the pastry has not been handled too much, the gluten does not develop and make it tough.
The pastry becomes crisp during baking as the gluten in the flour coagulates and becomes crisp with heat.
In a quiche, the egg is used to set the liquid filling. The egg denatures then coagulates with heat, becomes semi-solid and sets, forming a network which forms a matrix through the mixture.
If the egg mixture is over cooked, the protein denatures, coagulates and shrinks and squeezes out the liquid. This is called syneresis and makes the filling tough with holes.
This happens if the quiche or custard is cooked for too long at too high a temperature.

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Crème brûlée


Crème brûlée – Serves 4
This French dessert means ‘scorched cream’ as the sugar on the top is burned.

cremebrulee

Ingredients
300ml double cream
½ teaspoon vanilla essence
3 egg yolks
15g caster sugar
15g demerara or granulated sugar

Method

  1. Preheat the oven to 150°C/Gas 2 and put 2 small ramekins in a roasting tin half filled with water – called a bain marie.
  2. Warm the cream and vanilla essence in a small saucepan.
  3. Put the yolks and caster sugar in a bowl and mix in the warm cream.
  4. Pour the custard into 4 ramekins and bake in the bain marie until set – about 30 minutes.
    Cool and chill.
  5. Scatter the tops with demerara sugar and use the blow torch to caramelise the sugar.
  6. Hold the flame 5 cm away from the sugar at a 45° angle. The sugar caramelises, turns brown and bubbles.  The caramelised sugar becomes crisp when you cut it with a spoon.

The science bit

Eggs are used to set the custards in crème caramel and crème brûlée.
On heating the protein in the egg denatures, coagulates and sets forming a matrix structure which holds the milk or cream in place.
Gentle cooking using the water bath (bain marie) lets the egg proteins set evenly through the custard.
If you cook the custards on too high a temperature, the egg proteins set, shrink and curdle the mixture. This happens to scrambled egg. So your custards will have holes in them and be tough if they are cooked too long and at too high a temperature. This is called syneresis.

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French onion soup


French onion soup – Serves 2
To make French onion soup, you need to fry the onion until the natural sugars caramelise and the onions turn brown. This gives the soup its delicious flavour and sweet taste, and also provides colour.

Ingredients
25g butter or margarine
1 tablespoon oil (15g)
4 medium onions thinly sliced (450g)
1 tsp sugar
2 garlic cloves, thinly sliced
1 heaped tablespoon plain flour (30g)
600ml boiling water
1-2 beef or vegetable stock cubes
4 slices French bread (depending on size)
50g grated cheese

Method

  1. Melt the butter with the oil in a large heavy-based pan.
  2. Add the onions and stir and fry for 10 mins until soft, then sprinkle in the sugar, add the garlic and cook for 5 minutes until caramelised. The onions change to a golden brown colour and become sweet.
  3. Stir in the flour, add the boiling water and stock cubes and stir to thicken.  Cover and simmer for 10 minutes.
  4. To serve, toast the bread under the grill, scatter on the cheese and grill until bubbling.
  5. Spoon the soup into heat-proof bowls, float 2 slices of cheesy toast on top each bowl and serve.

The science bit

When the onions are heated, the sugars turn to caramel and the onions become brown.
The caramel gives the soup its brown colour and sweet flavour.
Flour is added to the soup liquid to thicken it. The starch in the flour gelatinises, swells and thickens the liquid.
The toast turns brown when it is toasted as dextrin is formed.
The cheese melts with heat, and the protein coagulates and shrinks.

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Welsh rarebit


Serves 2
Thanks to my friend Louise Johncox for this recipe. It was popular in her father’s tearoom and is a delicious lunchtime snack.

Ingredients
2 eggs
2 tablespoons milk
Pepper and salt to taste
120g grated Cheddar cheese
½ teaspoon mustard powder
2 slices of thick white bread

Method

  1. Mix together the eggs and milk with a fork and season with pepper and salt to taste. Stir in the grated cheese and add the mustard powder.
  2. Toast the bread on both sides and place on a baking tray. Cover one side of each slice of toast with the rarebit mixture.
  3. Grill until the topping is bubbling and golden brown.  Eat at once!
  4. You can add slices of tomato, poached egg, bacon and mushrooms to serve.

The science bit

Making toast shows dextrinisation as the starch changes to dextrin and goes brown.
The Maillard reaction develops more flavours in the toast.
Grilling the egg and cheese mixture makes the proteins coagulate as the egg and cheese change state and become solid.

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Guacamole


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

Ingredients
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

Method

  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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