Foods have different functional properties which can be treated and combined. They can be finished to improve palatability. Additives are used for a number of reasons and can be artificial or natural.
- thickens a liquid by forming a suspension such as a sauce
- forms a gel when the suspension is heated, like adding cornflour to a custard powder and milk mix
- flavours by sweetening
- colours by caramelising when heated
- aerates when beaten with a fat such as in a cake mix
- can coagulate which is when a liquid becomes firmer, for example when an egg is heated
- can aerate a mixture, like whisking egg whites in a meringue mix
- shortens pastry (makes it more crumbly) by making it less stretchy
- can act as an emulsifying agent to stop two liquids from separating
- moistens a baked mixture such as a cake
Some foods have different working properties when treated in certain ways. They can be treated by:
- Aerating incorporates air by sieving, creaming, whisking, beating, folding and rolling, or rubbing in. Raising agents can be used to make a mixture lighter, for example, baking power is used in cakes.
- Coagulation is when something thickens from a liquid to a solid. For example, raw eggs are clear and runny but become white and solid when heated.
- Preserving helps food to last longer through freezing, canning, jam-making, or pickling. Fats, sugar and oil are used in preserving.
- Tenderising tough meat makes it easier to eat. Lemon juice, vinegar or wine can be used as a marinade, or meat can be tenderised with mechanical action using a meat mallet or slow cooking.
- Thickening uses eggs, pulses, cereals and fruit to thicken liquids such as milk, and heat is usually applied. Egg custard is made like this.
Most of these working properties can be found in many different foods. The functional properties of different foods can be combined by:
- Binding uses fats, eggs, cereals and flour to bind ingredients. For example, egg is used to bind together a biscuit mixture.
- Bulking forms the main structure of a food product, such as flour in biscuits and cakes.
- Enrobing means coating a food with another ingredient, for example, dipping fish in beaten egg and then breadcrumbs.
- Enriching is the addition of an ingredient to improve the quality. Nutrients are sometimes added to increase nutritional value.
- Fermentation uses yeast to convert carbohydrates into alcohol and carbon dioxide. In bread making, yeast is added to flour and water causing the dough to rise.
- Flavouring can be savoury, like herbs and spices, or sweet, like sugar or sweeteners. Sugar helps to soften the sharp taste of grapefruit.
- Shortening uses of oils and fats to reduce the development of gluten in pastry to make the dough less stretchy.
- Stabilising helps food keep its structure. Eggs and flour are used for stabilising.
- Setting means using ingredients to make foods firm, such as gelatine to set cold desserts.
Finishing techniques are used to make the food look good. For example:
- Browning uses fats, eggs, sugar, milk, flour or oil, which darken a food when heated.
- Glazing adds a shiny coating, for example, pastry brushed with beaten egg before cooking.
- Icing can add colour and texture.
Finishing can help improve palatability, which is the appeal of the food, and includes taste, colour and smell.
When ingredients are combined they can form many different kinds of mixture or structure.
- Solution is when one substance is dissolve in another one, for example when sugar is dissolved in water we get a sugar solution.
- Colloid is a general term for when two substances are mixed together. For example milk has a colloidal structure, because it is made from microscopic drops of fat dispersed in a water-based liquid.
- Emulsion is when two unblendable liquids are mixed together, for example, oil and vinegar. An emulsifier like egg yolk is needed to stop them from separating. Emulsions are a particular type of colloid. Mayonnaise is an emulsion.
- Foam is when air bubbles are incorporated into a liquid, such as in whipped cream and meringue
- Gel contains a small amount of a solid in a large amount of liquid. A small amount of gelatine can set a large amount of liquid.
- Suspension is when a solid is held in a liquid. The solid may sink if the mixture is not stirred. Flour (solid) is suspended in milk (liquid) when making a cheese sauce.
Food additives can be classified as natural or artificial.
Natural additives occur naturally in foods. They are extracted and put into other foods. Caramelised sugar is used as colouring in cola.
Artificial additives do not occur naturally. They are made synthetically for a certain purposes. For example tartrazine is a synthetic colouring added to some sweets to make them yellow.
Uses for additives
Both natural and artificial additives are used for many different reasons:
- Preservatives extend the shelf life of a product. Salt is used used in bacon and sausages.
- Colouring makes food products look more appealing and appetising.
- Flavourings can be used to add or improve the flavour of a food product. Vanilla flavouring is often added to cakes and biscuits.
- Emulsifiers are used to prevent ingredients from separating. For example, lecithin, which is found in eggs, is used to stop the ingredients in mayonnaise from separating.