1. Functional and chemical properties
Carbohydrates
By the end of this lesson students should be able to:
• explain the term gelatinisation
• explain the term dextrinisation
• explain the term caramelisation.

2. Gelatinisation
The process in which moist heat is applied to starch grains, which swell, increase in size and then break open, releasing amylose, which thickens the mixture around boiling point.
Gelatinisation occurs between 75°C and 87°C
Stirring will prevent lumps forming.
When the thick liquid cools it forms a gel which will then set.
The presence of two molecules called amylose and amylopectin in starch gives it the ability to thicken sauces. They bond with each other when heated to form a gel:
Amylose causes sauces to thicken, turn cloudy when cooked and get even thicker as they cool.
Amylopectin produces a clear gel when it thickens and has the same thickness hot or cold.

3. Different starches contain different amounts of amylose and amylopectin molecules Cornflour made from maize cereal, for example, is almost pure starch and is high in amylose. This means it will form a strong gel. It blends to a smooth cream when mixed with a cold liquid
Starchy rich food
How they thicken
Wheat flour
Traditionally used to thicken white sauce (bechamel)
Cornflour
Used to thicken gravies, custard and soups
Arrowroot
Used to thicken gravies, soups, stews, sauces
Potatoes
Used to thicken soups and casseroles as they release starch
Tiny pasta shapes
Added to soups e.g. minestrone
Rice
Used to thicken milk puddings e.g. rice pudding
Barley
Added to a soups and casseroles to thicken it

4. Factors affecting gelatinisation
Amount of liquid: Small amount of liquid in proportion to starch will produce a thicker sauce and a large amount of liquid to proportion of starch will produce a runny sauce.
Type of starch: Cornflour is better for thickening than plain wheat flour, as it is pure starch.
Temperature: gelatinisation requires hot, moist conditions. Starch will not dissolve on cold water and cannot thicken cool liquids. In order for starch to absorb liquid the outside of the starch grain need to be softened by heating. At a temperature between 75°C and 87°C the sauce will start to thicken and at boiling point it stops thickening. Sauces should be gently boiled while stirring for a full 2 minutes to ensure that all the starch grains have gelatinised.
Stirring: is essential for the creation of a smooth gelatinised sauce. If not stirred the starch grains will settle at the bottom of the saucepan. Here the grains will absorb some of the liquid around them, but they will also stop liquid from reaching other grains, resulting in a lumpy texture.
Sugar: competes with starch for water. This means the starch does not absorb as much water as it could. Sugar makes the sauce runnier and less likely to be stable. Always add sugar after gelatinisation in sauce-making.
Acids: such as lemon juice should always be added to the sauce after it has thickened and boiled, because they can break down the gel. Recipes like lemon meringue pie should follow this method.

5. Critical stages when making a starch based sauces

6. Dextrinisation
Dextrinisation occurs when starch is broken down into dextrin by dry heat, e.g. baking, grilling or toasting. Dextrin adds a sweet taste to baked products.
Dextrinisation contributes to the brown/ golden brown colour and flavour of many foods such as toast, bread, pasties, biscuits, cakes, scones
When you toast bread until it is very dark in colour, it means that it has gone past the dextrinisation stage and the oxygen and hydrogen part of the carbohydrate have been driven out by the heat as water and what is left behind is the carbon.   

7. Caramelisation
Caramelisation is the process of changing the flavour and colour of food products containing sugar from white to brown when heated. It can give a buttery, toasty or even a nutty flavour to food.
Caramelisation is one of the most important types of browning processes in foods.
It leads to a desirable golden brown colour and an attractive flavour in baked goods and drinks.
Process: When sugar is heated to high temperatures (at least °C), it first melts, then forms a syrup and boils. Water is released from the sugar as steam when it is heated. The colour of the sugar gradually changes from colourless and clear to golden brown to dark brown and eventually black and bitter when it is overheated. Sugar begins to break down to pure carbon at about 200°C.
When cooled the syrup becomes brittle and hard.
Examples:
Fudge, toffee, jam, honeycomb, brandy snaps
Crème brulee, Crème caramel, spun sugar
Surface of biscuits, bread, pastry
Vegetables such as onions when fried for extended period of time e.g. French onion soup
Crème brulée is a dessert that has a hard sugar topping. This is achieved by using a blow torch or a very hot grill to caramelise the sugar.