Milk, cheese and yoghurt (dairy) as a food commodity group: their nutritional value, the main types, heat treatment of milk, working characteristics such as coagulation, and safe storage.

What this dot point is asking

You need to know what milk, cheese and yoghurt provide in the diet, the main types, how milk is heat-treated to make it safe, how dairy foods behave in cooking (their working characteristics), and how to store these high-risk foods safely.

What this group gives us in the diet

Dairy foods are a key source of calcium, which works with vitamin D to build and maintain strong bones and teeth and is especially important during growth. They provide high biological value (HBV) protein for growth and repair, vitamin A and B vitamins (including B12), and energy from milk fat. They form their own section on the Eatwell Guide.

Full-fat dairy is high in saturated fat, so the advice is to choose lower fat versions (semi-skimmed or skimmed milk, reduced-fat cheese, low-fat yoghurt), which keep the calcium and protein but cut the saturated fat.

The main types

• Milk: whole (full-fat), semi-skimmed and skimmed, plus alternatives such as soya, oat and almond drinks (which are often fortified with calcium).
• Cheese: hard cheeses (Cheddar), soft cheeses (Brie, cream cheese) and cottage cheese; cheese is made by coagulating (clotting) the milk protein, usually with rennet, then separating the curds from the whey.
• Yoghurt: made by adding harmless bacteria to warm milk, which ferment the lactose to lactic acid, thickening the milk and giving the sour taste.

Heat treatment of milk

Raw milk can carry harmful bacteria, so most milk is heat-treated:

• Pasteurisation: heated to about 72 degrees Celsius for 15 seconds, then cooled quickly. This kills most harmful bacteria, makes the milk safe, and extends shelf life, with little change to flavour or nutrients.
• UHT (ultra-heat treatment): heated to about 132 degrees Celsius for a few seconds, giving long-life milk that keeps unopened without refrigeration.
• Sterilised milk is heated in the bottle to a high temperature for longer, which keeps well but changes the flavour.

Working characteristics

Coagulation

The protein in milk and cheese sets (coagulates) when heated or when acid is added. This is used to make cheese, to thicken custards and to set sauces. Overheating can cause cheese to become stringy and oily as the protein tightens and squeezes out the fat.

Browning

Cheese browns under a grill or in the oven, giving colour and flavour to dishes such as cauliflower cheese and lasagne.

Emulsification

Milk and cream are emulsions of fat in water, which helps them combine with other ingredients and gives sauces a smooth, creamy texture.

Storing dairy foods

• Milk, cheese and yoghurt are high-risk foods and must be kept in the fridge below 5 degrees Celsius.
• Keep them covered and away from raw meat to avoid cross-contamination.
• Use within the use-by date, as dairy supports the growth of harmful bacteria.
• UHT and sterilised milk keep at room temperature until opened, then must be refrigerated and used quickly.