The Science of Starch Fact Sheet

Starch has many useful properties such as:

·  A thickening agent in stews and sauces

·  A bulking agent (forms the bulk of a product such as bread, cakes, rice in stuffed vegetables)

·  A gelling agent (e.g. translucent shiny gloss on a fruit flan).

Pectin (used in jam making) and gelatine are also thickening agents.

Common food starches are:

·  Potatoes

·  Wheat flour – plain, self-raising and strong

·  Maize (corn) flour

·  Rice

·  Cassava (tapioca flour).

How does it work – the facts

Fact – Starch forms a suspension in water until heat is added. When the temperature reaches around 60°C the starch granules begin to absorb water.

Fact – As the temperature rise to around 85°C the starch granules will have absorbed up to five times their volume of water.

Fact – Eventually the starch grains swell up until they become weak and break. They make a network of starch and swollen granules with the water. This is called a gel. The whole process is called gelatinisation.

Fact – Continued heating makes sure that all the starch granules have swollen and complete gelatinisation has taken place.

Fact – When the starch granules rupture starch is released and the thickness or viscosity of the mix begins to increase.

Fact – Sauces need to be stirred continually when it is heated, otherwise the starch settles to the base on the saucepan and the sauce becomes lumpy.

Fact – When the starch gel cools the mixture becomes thicker.

Fact – The higher the ratio of starch to liquid the thicker the gel becomes.

Fact – The gelatinisation of starch is also used to help make baked products e.g. bread, cakes and pastry. The starch granules absorb moisture from the dough, as the temperature rise during baking they gelatinise.

Examples: Meat and Education recipes

Pork and beetroot tartlets Ham, spring onion & basil muffins Tortilla lasagne

Pupil Name: Date:

Activities

1.  Using magazines, recipe books or websites, research the following foods and state which type of starch is used and what their function is. The first one has been done for you.

Macaroni cheese / Plain flour
Thickening agent / Lemon meringue pie (filling)
Lasagne cheese sauce / Chicken and mushroom pie (filling)
Leek and potato soup / Spinach, potato and chickpea curry
Risotto / Gravy

2.  Using the information on the fact sheet, explain in your own words how starch thickens a sauce.

3.  You have made a beef lasagne and the white sauce is lumpy. Using the information on the fact sheet, explain how this could be avoided next time.