Dairy - EdExcel Specification

The key facts from the Dairy topic.

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Processing of milk

Pasteurised - blue lid - kills pathogenic micro-organisms - 72C for 5 seconds then cooled rapidly.

Skimmed - red lid - same as pasteurised.

Semi-skimmed - green lid - same as pasteurised.

Homogenised - red lid - fat globules are broken up so they are equally suspended - then pasteurised.

UHT - pink lid - kills all micro-organisms - 132C for 1 second.

Sterilised - Heated to above 100C for 30 minutes.

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Structure of milk

Milk is made up of:

Water

Carbohydrates

Fat

Protein

Minerals, especially Calcium

Vitamins, especially B group.

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Nutritional Information

Whole Semi-skimmed Skimmed

Protein 3.2g 3.4g 3.4g

Carbohydrate 4.7g 5g 5g

Fat 4g 1.7g 0.1g

Calcium 119mg 122mg 124mg

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Putrefaction

When milk bacteria use lactose as an energy source, they change it into lactic acid, which makes the milk taste sour.

To produce lactic acid the bacteria must first split lactose into its 2 components, glucose and galactose.

These can diffuse into bacterial cells and be used as energy sources.

The principal protein of milk - casein - turns into curd in this acid environment, so another way of describing sour milk is to say that it has 'curdled'.

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Storage

Kept cool and covered.

Should be in a dark place.

Date-stamped must be kept in fridge.

Clean containers must be used to package.

Not left in a warm and sunny environment.

Old and new must not be mixed together.

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Secondary processing of milk

Cream - produced from whole milk by a process of separation.

Yoghurt: Fluid yoghurt such as Greek - whole or skimmed milk. Semi-solid yoghurt - whole or skimmed is partially evaporated and skimmed milk powder may be added.

Ice-Cream - Egg-custard sauce mixed with cream.

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Legal minimum fat content of cream %

Half cream 12

Single 18

Whipping 35

Double 48

Thick double 48

Sterilised 23

'Long life' single 18

'Long life' whipping 35

Clotted 55

Soured 18

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Butter

Made by churning cream.

When shaken or churned, the fat globules clump together to form butter.

The excess liquid separates and is drained off as buttermilk.

The butter is a water-in-oil emulsion containing about 82% fat.

By law, the butter in Britain must have a minimum fat content of 80% and a maximum water content of 16%.

Most butter has 3% salt added, although some is left unsalted.

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Manufacture of margarine

1. Refining of oils

2, Hydrogenation of oils

3. Blending of oils

4. Pasteurisation and inoculation of fat-free milk and whey

5. Salt is added

6. Formation of emulsion

7. Formation of fat crystals

8. Packing.

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Production of cheddar cheese

1. Delivery of milk

2. Pasteurisation

3. The ripening of the milk

4. Renneting

5. Cutting the curd

6. Scalding

7. Pitching (Setting)

8. Cheddaring

9. Milling and Salting

10. Moulding

11. Pressing

12. Ripening

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Varieties of hard cheese

Factors affecting texture: degree of acidity, temperature, amount of pressure, length of time in the press.

Factors affecting flavour: Amount of pressure, ripening time.

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Soft cheese

Ripened made from whole milk. Stronger flavour e.g. Brie, Camembert.

Unripened milder flavour e.g. curd, cream cheese.

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Composition of cheese

Protein - 50g provides one fifth required each day by adults.

Also supplies valuable amounts of Calcium, Phosphorous and Vitamin A.

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