What is a raw material and what is in it?
A raw material is the food we start with. Most foods are made of the same few parts:
- Water: makes food soft and lets germs grow.
- Starch (carbohydrate): energy store in grains, potatoes and tubers.
- Protein: in pulses, milk, eggs, meat and fish. Heat changes it (it sets, like a boiled egg).
- Fat/oil: in nuts, oilseeds, milk and meat. It can turn bad (rancid) with air.
- Vitamins, minerals, fibre, colour and flavour.
Properties of common raw materials
| Raw material | Main property | Usual processing |
|---|---|---|
| Cereals (wheat, rice) | Dry, hard, starch-rich; keep well | Cleaning, milling, polishing, cooking |
| Pulses and soya | Protein-rich, dry | Soaking, splitting, cooking, grinding |
| Tubers (potato, cassava) | Starch, about 75% water; spoil soon | Washing, peeling, frying, drying |
| Fruit and vegetables | Water, sugar, acids; go brown when cut | Washing, cutting, heating, juice, drying |
| Milk | About 87% water; spoils in hours | Cooling, pasteurising, making curd and cheese |
| Meat and fish | Protein-rich, very perishable | Chilling, freezing, curing, cooking |
Rule: more water means faster spoiling, so wet foods need quick, careful processing.
The main principles of processing
- Change the size: cutting, grinding, crushing. Smaller pieces have more surface for heat and water to act on.
- Use heat: cooking, boiling, baking, frying. Heat kills germs, softens food and brings out flavour. Pasteurising uses a mild heat (about 72 °C for 15 seconds for milk) so food stays fresh.
- Remove water: drying or adding sugar or salt. Germs need water, so dry food keeps long.
- Use cold: chilling and freezing slow germs down.
- Mix and shape: mixing, kneading, moulding make dough, batter and sauces.
- Separate: sieving, filtering, pressing take out what we do not want (bran, seeds, juice from pulp).
- Use friendly germs: fermentation turns milk into curd and batter into idli.
- Pack: keeps dirt, air and water out.
Choosing the method and counting the result
The best method depends on the raw material, what product we want and cost. Always clean and sort (grade) raw material first, because dirt and bad pieces spoil the whole batch.
Yield = output ÷ input × 100. Some mass is always lost as peel, bran, water or waste.
Moisture content tells how much of the food is water. In drying, the dry matter (solids) stays the same; only water leaves. So: final mass = solids ÷ (1 − final water fraction).
Try it
Take two equal slices of apple. Leave one whole slice and cut the other into small cubes. Put both on a plate in the sun for a few hours. Which dries faster and why? Then in the 3D, set pieces to the smallest size and move the water slider down to see the same idea.
Key formulas and definitions
- Yield (%) = output ÷ input × 100
- Solids = total mass × (1 − water fraction)
- Final mass after drying = solids ÷ (1 − final water fraction)
- Cube of side a: surface area = 6a²
- Pasteurising milk: about 72 °C for 15 s
Worked examples
1. A cube of potato has side 4 cm. It is cut into 8 equal cubes of side 2 cm. How does the total surface area change?
Before: 6 × 4² = 96 cm². After: 8 × (6 × 2²) = 8 × 24 = 192 cm². The surface area doubles, so it dries and cooks faster.
2. 100 kg of fruit has 80% water. It is dried until it has 20% water. What is the final mass?
Solids = 100 × 0.20 = 20 kg. Final mass = 20 ÷ (1 − 0.20) = 20 ÷ 0.8 = 25 kg. Water removed = 75 kg.
3. A mill gets 400 kg wheat and produces 288 kg flour. Find the yield and the mass lost as bran and waste.
Yield = 288 ÷ 400 × 100 = 72%. Lost = 400 − 288 = 112 kg.
Common mistakes
- Thinking drying removes the solids too. Only water leaves; solids stay the same.
- Thinking heat only cooks. Heat also kills germs, but heat that is too strong spoils colour, taste and vitamins.
- Using the wrong method for the material, such as leaving wet milk unheated for hours.
- Forgetting that yield is less than 100% because peel, bran and water are lost.