Carbohydrates Flashcards
What is gelatinisation
The swelling of starch granules when they are heated with a liquid to the point where they burst and release starch molecules
What happens during gelatinisation
Made of thousands of glucose molecules in chains
At 60° they start to absorb water making them get bigger
80° the granules are so swollen they start to burst and release starch molecules
The starch molecules trap water molecules and stop them moving around so much
At 100° sauce completely thickens
As the sauce cools down the starch molecules form longer chains trapping the water molecules so it gradually becomes a solid gel
Given example of gelatinisation when foods containing starch are cooked
Cooking pasta
Why is it important to stir regularly when cooking a sauce
To stop the starch molecules staying at the bottom where they would swell up, stick together and cause the sauce to have a lumpy texture
What is dextrinisation
When starch molecules break up into smaller groups of glucose molecules when they are exposed to dry heat
What happens in dextrinisation
Dry heat causes starch molecules to break into groups of smaller glucose molecules dextrin.
The formation of dextrin contributes to the flavour
Give an example of dextrinisation.
Toasting bread
Why does toast sometimes burn
Carbohydrates are made from carbon, hydrogen and oxygen. When the starch molecules are expose to dry heat for too long, the oxygen and hydrogen have been driven off so only the carbon is left
What is caramelisation
When sucrose (sugar) molecules are heated, they change colour, flavour and texture of the sugar as it turns into caramel
What happens during caramelisation
Sugar that is used in cooking is a disaccharide made from glucose and fructose
When it is heated it, melts, then forms a syrup and boils
The molecules of sucrose start to break up
As sugar is a carbohydrate, it is made from hydrogen, oxygen and carbon. As the sugar is heated, the hydrogen and oxygen bond to make water which evaporates gradually. This leaves the carbon which is why the caramel gets darker
How does the texture of sugar change during caramelisation
It begins as crystals of sugar, then to a syrup, and finally a brittle toffee as it cools
What happens if you start the syrup
It will crystallise into larger, hard lumps
What is the temperature of caramelising sugar
160°C to 170°C
Given example of caramelised sugar in a recipe
Crème brûlée, frying onions, roasting vegetables
What is the difference between caramelisation
Dextrinisation is when starch is browned I heat and caramelisation is when sugar is browned by heat
