1. Functional and chemical properties
Carbohydrates

2. Lesson objectives
By the end of this lesson students should be able to: • explain the term gelatinisation • explain the term dextrinisation • explain the term caramelisation.

3. The effect of temperature, acid and sugar on gelatinisation
Resources for each group
100g cornflour
1 litre water
30ml lemon juice
50g sugar
Thermometer
Wooden spoon
Saucepan
4 small bowls
Sticky labels

4. Gelatinisation Process
Make a sauce using 250ml of water with 25g cornflour. Moisten a small amount of cornflour with water. Stir until the lumps disappear, add the remaining liquid and stir.
Place the mixture in a saucepan. Heat and stir constantly.
Bring the mixture to the boil for two minutes. Stir constantly.
Remove from heat and pour into a small bowl. Label ‘Control’.
Repeat sauce-making process. Boil for two minutes and add the lemon juice, Boil for a further minute. Pour into a small bowl. Label ‘Gel with acid’.
Repeat sauce-making process. Boil for two minutes add sugar. Boil for a further minute. Pour into a small bowl. Label ‘Gel with sugar’.
Repeat sauce-making process, except do not boil the sauce – heat to 70°C only. Remove from the heat. Pour into a small bowl. Label ‘Gel at 70°C’.

5. Gelatinisation Questions
Describe the effect of adding lemon juice to the sauce.
Describe the effect of adding sugar to the sauce.
Explain how temperature affected the thickness of the sauce.
What advice would you give to someone making a sweet lemon sauce?

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 colour and flavour of many foods such as toast, bread and croissants.
Browning on the surface of bread is dextrinisation.

7. Caramelisation
Caramelisation is one of the most important types of browning processes in foods.
Caramelisation is the process of changing the colour of sugar from white to brown when heated.
Caramelisation causes important changes in foods, not only in colour but also in flavour.
It leads to a desirable golden brown colour and an attractive flavour in baked goods and drinks.
Caramelisation can give a buttery, toasty or even a nutty flavour to food.
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.

8. Critical stages when making a starch based sauces