Section C: Cooking and food preparation

Section C: Cooking and food preparation Topic 1: Food science – working characteristics and the functional and chemical properties of ingredients

Characteristics and functional and chemical properties of ingredients • Learning objectives • To develop a knowledge and understanding of: • The working characteristics and the functional and chemical properties of ingredients.

Functions of ingredients Every ingredient used in a recipe has a specific function, for example to: • Thicken • Aerate • Coagulate • Add nutritional value. Most food products we make contain more than one ingredient. A colloidal structure is formed when two or more ingredients are mixed together.

Functional properties of carbohydrate foods • Wheat flour is the most common starchy foods used in cooking. • Flour: • Forms the main structure of a product, e.g. in cakes, pastry and biscuits • Bulks out the ingredients. • The flour used will vary depending on the desired texture and the product you are making.

The effect of dry heat on flour • When dry heat is used on flour the product becomes brown – this is called dextrinisation. • Examples of this are seen when baking or toasting. • The dry heat converts the starch into a sugar.

The effect of moist heat on flour • When flour is mixed with a liquid and heat is applied it will thicken. This is called gelatinisation. • Starch grains do not dissolve in water, they form a suspension. • As the liquid is heated, the starch grains swell (60°C). • As more heat is applied, the starch grains burst and thicken the mixture (80°C). • The mixture must be stirred as it is being heated to prevent lumps from forming.

Flour as a thickener • Flour can be used to thicken sauces in cooking. • Cornflour is often used as an alternative to flour in sauces. • All sauces need to be stirred as they are heated so that lumps do not form. • Other starch foods that thicken mixtures include potatoes, other root vegetables, rice and arrowroot.

Sugars • Sugars: • Add flavour – most sugars taste sweet. Lactose is thesugar in milk – this does not taste sweet • Add colour.

Heat on sugars • When heat is applied it melts and becomes a syrup. • At 154°C it starts to change colour – this is called caramelisation. • The longer the sugar is heated, the darker it becomes and the harder it sets. • Maillard reaction – this is when sugars are mixed with other products (e.g. eggs and flour) and baked. This is a type of browning.

Uses of sugar • Bulking out ingredients, e.g. in biscuits and rubbed-in mixtures. • Aerating – when sugar is beaten with eggs or fats, air is added to the mixture. When heat is applied, the air expands and causes the mixture to rise. • Preserving –high concentration of sugar prevents growth of micro-organisms. • Helps with fermentation, e.g. when making bread.

Uses of fats • There is a wide range of fats used for a variety of purposes. • Not all fats melt at the same temperature. This property is called plasticity. • Some products are designed to have a lower melting point as this gives consumers a quality in a product that they want, e.g. a spread that can spread straight from the fridge.

Use of fats • Aeration – fat and sugar are creamed together, trapping air which expands on heating, e.g. in creamed cake mixtures.

Uses of fats • Shortening –fat coats the grains of flour and prevents the gluten from developing. The finished product will have a short crumbly texture, e.g. in pastry. • Flavour and moisture –some fats are used for flavour, e.g. butter. They will also add moisture to foods – this means they have a longer shelf life.

Uses of fats • Emulsions –these are formed when oil and a liquid are mixed together, e.g. in a salad dressing. • Emulsifying agents are sometimes added to stop mixtures separating, e.g. in low-fat spreads.

Cooking foods • Fats can be used to cook food. • Shallow, deep and stir frying – food has a crisp texture and added flavour. • Sautéing allows the flavour to develop in the foods as they are cooked for a longer time. • Roasting is often used for meat and vegetables.

Protein – eggs • Coagulating (setting) • When moist or dry heat is applied to eggs the protein (albumin) in the eggs coagulates (sets). • Egg white starts to coagulate at 60°C. • Egg yolk starts to coagulate at 80°C. • Syneresis occurs when protein is overcooked.

Uses of eggs • Aeration –when eggs are whisked the albumin stretches and traps air. • If the egg whites are left to stand they collapse. • Whisking egg whites can also be called a foam as it is a mixture of gas (air) and liquid (egg white). • Eggs add colour, e.g. when used in a sauce or as a garnish. • Eggs form an emulsion when mixed with fat. This stops it separating, e.g. in mayonnaise.

Uses of eggs • Binding, e.g. in rubbed-in cake or scone mixtures or fishcakes. Protein sets the mixture when heated. • Glazing produces a shiny surface, making the food more attractive. • Coating – eggs allow a coating to be applied to a product, e.g. breadcrumbs. When heated the eggs set, holding the coating in place. • Enriching (adding nutrients), e.g. when added to a sauce, pastry or bread mixture.

Gluten • When making cakes, a soft flour is used which has a low gluten content so that the cakes have a soft crumb. • When making bread, strong flour with a high gluten content is used to provide the structure. The gluten is developed in the bread dough when it is being kneaded. • The names of the proteins found in wheat which form gluten are: • Gliadin • Glutenin.

Acids – denature protein • Acids are chemicals found in some foods. • Acids give flavour to foods – sour or sharp. • Acids can also be used to tenderise meat. They break down the structure of the protein.

Fruits and vegetables • Lemon juice is acetic acid. It is used to: • Prevent foods going brown – foods such as apples and bananas go brown when they have been cut. This is called enzymic browning. If the fruit is put in a lemon juice solution the browning does not take place • Set mixtures that contain protein, for example cheesecakes. Lemon juice is also added to some jams to help them set (form a gel).

Types of raising agent • The gases used are air, carbon dioxide or water vapour. • Gases are introduced to the mixture and expand on heating. • The different types of raising agents used in cooking are air, carbon dioxide, self-raising flour, yeast, steam.

Types of raising agent • Yeast • When yeast is given the right conditions – food, warmth, moisture and time – it can break down food into carbon dioxide by a process known as fermentation. • Yeast is used to make bread. You can use either fresh or dried yeast.

They must be used in the correct proportion. The table below shows what happens if too much or too little is used. Chemical raising agents

Chemical raising agents • Carbon dioxide • This is introduced by using: • Bicarbonate of soda • Bicarbonate of soda + acid • Baking powder. • Self-raising flour • This is soft flour + raising agent.

Air • The diagram below shows how air can be added.

Steam • Steam is produced when products are baked from the liquid present in the mixture. • Steam is used as a raising agent in products which contain a lot of liquid, for example in: • Batters • Choux pastries • Flaky and puff pastry. • These products have to be cooked in hot • ovens so that sufficient steam is produced to • make the product rise.

Types of raising agent • Carbon dioxide – this is introduced by using: • Bicarbonate of soda • Bicarbonate of soda + acid • Baking powder. • Self-raising flour – soft flour + raising agent. • Yeast –used for bread making. You can use either fresh or dried yeast. • Water vapour (steam) – steam is produced from the liquids in the mixture.It is used in choux pastry, batters, cakes, flaky and puff pastry.

Key words • Aeration: the process of trapping air in a mixture. • Albumin: protein in egg white. • Caramelisation: process of changing the colour of sugar from white to brown when heated. • Coagulate: to set; the change in structure of protein brought about by heat, mechanical action or acids. • Colloidal structure: when two substances are mixed together. • Denatures: changes which occur in proteins. • Dextrinisation: when dry heat is applied to flour and it browns as the starch is changed into a sugar.

Key words • Emulsifier: a substance that stops oil and water separating. • Emulsion: a mixture of two liquids. • Enzymic browning: reaction between a food product and oxygen resulting in a brown colour. • Gelatinisation: what happens to starches and water when cooked together. • Gluten: the protein in flour. • Maillard reaction: when foods containing proteins and carbohydrates are cooked by dry methods.

Key words • Oxidisation: occurs when fruit and vegetables are cut and the cells are exposed to air. • Radiation: where heat is passed by electromagnetic waves from one place to another. • Shortening: when fat coats the flour grains and prevents the gluten from developing and absorbing water, resulting in a crumbly mixture. • Syneresis: usually refers to eggs; if overcooked, the proteins shrink as they coagulate and separate from the watery liquid.

Section C: Cooking and food preparation