- Created by: eloisesmallbone07
- Created on: 18-01-20 15:35
· Gelatinisation helps to thicken foods that contain starch
· When starch granules are first mixed with liquid, they become suspended in it
· When the granules are heated with water, the bonds between starch molecules start to break, allowing water molecules to enter. As water is absorbed, the starch granules well in size and soften.
· Between 60 and 80 degrees, the starch granules burst open and release their starch into the liquid
· This release of starch causes the liquid to thicken. How thick the liquid becomes depends on the ratio of starch to liquid in the mixture.
· When it cools, the liquid solidifies and a solid gel is formed- this is useful for making ‘set’ desserts
· Gelatinisation also happens when you cook starchy foods like pasta and rice- they swell, soften and release starch into the water as they cook
· When starchy foods such as bread or biscuits are cooked with dry heat, the starch molecules in the food break down into smaller molecules called dextrins.
· This breakdown is called dextrinization and it gives food a browner colour and crispier texture as well as a different taste
· The longer the food is cooked, the more starch is converted into dextrin and the darker and crispier the food becomes
· Sugar molecules break down when they reach a high temperature- this causes sugar to turn brown and change flavour. This process is called caramelisation.
· The sugar goes through various stages: at first the liquid is runny and has a very sweet taste, as time passes it becomes more like a smooth caramel, eventually it turns harder and as it cools it becomes more like a boiled sweet.
· Caramelised sugar can burn very quickly, turning black, brittle and bitter to taste.
· To avoid this, water can be added during the early stages of heating
· When fats such as butter are beaten with sugar (creaming) air becomes trapped in the mixture. This air makes the mixture fluffier and lighter in colour.
· This aeration gives cakes a spongy and light texture when they’re cooked.
· Foods can be aerated in many different ways, e.g. whisking egg whites
· When you rub fat into flour, you cover the flour particles with fat- this gives the flour particles a waterproof coating.
· This coating prevents long gluten molecules forming when water is added to the flour.
· This means the dough cannot become stretchy and baked goods like shortbread keep a firm and crumbly texture
· Shortening is also used when making filled pies and tarts- it’s helpful because the base doesn’t rise and forms a solid case
· Some fats are called ‘shortening’- they have 100% fat content which helps stop gluten formation and prevents steam from raising the food.
· Fats have plasticity- we’re able to spread and manipulate them.
· This is possible because fats contain a mixture of different triglycerides. These different triglycerides all melt at different temperatures- so fats gradually soften over a range of temperatures rather than melting at just one.
· The more plasticity a fat has, the easier it is to spread.
· Plasticity is useful for: decorating cakes with buttercream, rubbing fat into flour, spreading butter and putting cream cheese on crackers
· Emulsions are formed when oily and watery liquids are shaken together
· Milk, margarine and mayonnaise are all examples of emulsions.
· Usually, oil and water don’t mix together and so emulsions separate out again unless you keep shaking or stirring them- or use an emulsifier.
· The molecules in an emulsifier have two different ends: one is hydrophilic (attracted to water) and the other is hydrophobic (repulsed by water).
· When you add an emulsifier, the water molecules bond to the hydrophilic side and the oil molecules bond to the hydrophobic side. This holds the oil and water together in a stable emulsion, preventing them from separating.
· Emulsions can either be oil-in-water or water-in-oil
· Egg yolks contain a natural emulsifier called lecithin- this is used as the emulsifier in margarine and mayonnaise.
· Emulsions are often used as sauces and salad dressings