Gelatinisation

Gels are systems where large volumes of liquids are held by a small amount of solid.

Gelatinisation occurs when starch (flour) is added to a liquid and heated e.g sauce making using the blended method. This method is used to produce sauces made from cornflour and custard powder.

The cornflour is blended with a small quantity of cold liquid before being added to the remaining liquid and heated.

When starch is added to cold liquid it does not dissolve because the starch granules are suspended in the liquid.

When the mixture is heated slowly and stirred, the starch granules start to soften- heating starts the process of gelatinisation. The starch granules fill with water and with further heating they start to move more rapidly and the molecule bonds weaken.

As more liquid enters the granules it becomes trapped and so the filling begins to thicken.

The starch granules can swell about 5x their normal size, almost touching each other.

Gelatinisation occurs between 75 and 87 degrees. The mixture must be boiled for 2 minutes to ensure all starch is fully gelatinised.

The amylose molecules are involved in the process of gelatinisation as they will seep from the starch grains and stay in the liquid as long as it remains hot.

Any ungelatinised starch will give a raw taste to the sauce. 

Acid such as lemon juice or vinegar will prevent the starch granules from thickening because it breaks the starch molecules down into smaller molecules.