Primary Processing

This lesson covers primary processing of food, as required by the AQA GCSE Food Preparation and Nutrition specification (8585), section 3.6. You need to understand what primary processing means and study specific examples, including the milling of wheat into flour and the heat treatment of milk (pasteurisation, UHT, sterilisation and micro-filtration).

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What Is Primary Processing?

Primary processing is the first stage of transforming raw agricultural materials into basic food ingredients that can then be used in cooking or further processed into food products.

Feature	Detail
Definition	Converting raw materials from farms into basic ingredients
Examples	Milling wheat → flour; milking cows → liquid milk; slaughtering cattle → beef cuts; harvesting sugar cane → raw sugar
Purpose	Makes raw materials safe, edible and suitable for storage, transport and further processing
Differs from secondary processing	Primary processing produces ingredients; secondary processing produces food products (bread, cheese, cakes)

flowchart LR
    A["RAW MATERIAL<br/>(from farm)"] --> B["PRIMARY<br/>PROCESSING"]
    B --> C["BASIC<br/>INGREDIENT"]
    C --> D["SECONDARY<br/>PROCESSING"]
    D --> E["FOOD<br/>PRODUCT"]

    A1["Wheat"] --> B1["Milling"] --> C1["Flour"]
    A2["Milk from cow"] --> B2["Heat treatment"] --> C2["Pasteurised milk"]
    A3["Sugar cane"] --> B3["Extraction &<br/>crystallisation"] --> C3["Sugar"]

    style B fill:#3498db,color:#fff
    style D fill:#8e44ad,color:#fff

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Milling Wheat into Flour

Milling is the process of grinding wheat grains into flour. This is one of the most important primary processes, as flour is a fundamental ingredient in bread, cakes, pastry, pasta and many other products.

Structure of a Wheat Grain

Part	Description	Proportion
Endosperm	The largest part; starchy white interior; contains most of the carbohydrate and protein (gluten)	~83%
Bran	The outer protective layers; rich in fibre, B vitamins and minerals	~14.5%
Germ (embryo)	The reproductive part; rich in B vitamins, vitamin E, fat and protein	~2.5%

The Milling Process

Step	Description
1. Cleaning	Wheat grains are cleaned to remove dirt, stones and other impurities
2. Conditioning	Grains are moistened with water to toughen the bran (making it easier to separate) and soften the endosperm
3. Breaking	Grains pass between steel rollers that crack open the grain and separate the bran from the endosperm
4. Sieving	The broken grain is sieved to separate different particle sizes; bran and germ are removed
5. Reduction	The endosperm particles are gradually ground finer by successive pairs of rollers
6. Sieving (repeated)	After each reduction stage, the flour is sieved again; finer particles become white flour
7. Blending	Different flour streams are blended to produce the desired type (plain, self-raising, strong bread flour)

Types of Flour

Type	What It Contains	Uses
White flour	Endosperm only (bran and germ removed)	Cakes, pastry, sauces, white bread
Wholemeal flour	All three parts (endosperm, bran, germ)	Wholemeal bread, biscuits, pastry
Brown flour	Some bran retained (typically 85% extraction)	Brown bread; compromise between white and wholemeal
Strong flour	High-protein white flour (from hard wheat varieties)	Bread making — more gluten for structure
Self-raising flour	White flour with added baking powder (raising agent)	Cakes, scones, sponges

Fortification of Flour

In the UK, white flour (but not wholemeal) must by law be fortified with certain nutrients that are lost when the bran and germ are removed during milling:

Nutrient Added	Why
Calcium (calcium carbonate)	To compensate for the calcium lost with the bran; supports bone health
Iron	Lost during milling; essential for red blood cell production
Thiamin (vitamin B1)	Lost during milling; essential for energy release from carbohydrates
Niacin (vitamin B3)	Lost during milling; essential for energy release and nervous system function

Exam Tip: Know the four nutrients that must be added to white flour by law: calcium, iron, thiamin (B1) and niacin (B3). This is a commonly examined fact.

Wholemeal flour does not need fortification because it retains all parts of the grain, including the nutrient-rich bran and germ. However, since 2024, folic acid is also being added to non-wholemeal wheat flour in the UK to help prevent neural tube defects in babies.

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Heat Treatment of Milk

Milk undergoes heat treatment during primary processing to make it safe to drink by killing harmful bacteria. There are several methods, each with different temperatures, times and effects.

Why Milk Needs Heat Treatment