The big idea: a production line
Food manufacturing means making food in a planned line of stages, so that every batch is the same, safe and tasty. Each product has raw material at the start, a few process stages in the middle and a finished product at the end.
- Clean: wash, sort and remove dirt or stones.
- Change: cut, crush, cook, set or ferment.
- Control: keep the right temperature and time.
- Close: pack in a clean, sealed pack and label it.
Workers wear clean clothes, wash hands and keep tools clean. This is called hygiene. It matters as much as the machines.
Grains and wheat flour
A grain has an outer bran layer, a starchy middle (endosperm) and a small germ.
Making flour
- Clean the wheat: remove stones, dust and husk.
- Condition: add a little water so the bran toughens and the middle softens.
- Mill: rollers or stones crush the grain.
- Sieve: fine flour falls through; coarse bran stays.
White flour (maida) is mostly endosperm. Whole-wheat flour (atta) keeps the bran and germ, so it has more fibre.
From flour to food
- Bread: flour, water, salt and yeast. Mix, knead, rise, bake.
- Noodles: flour and water kneaded, rolled and cut, then dried or steamed.
- Biscuits: flour, fat and sugar mixed, shaped and baked dry.
Rice is milled to remove the husk (brown rice) and then the bran (white rice). Maize and millets are milled in much the same way.
Beans and tubers
Soybean to tofu
- Soak soybeans in water until they swell.
- Grind them with water into a slurry.
- Boil and strain: the liquid is soy milk, the leftover is okara.
- Add a setting agent (a mineral salt or an acid). The protein clumps.
- Press out the water. The block is tofu.
Other bean foods: dal (split and dehusked pulses), bean paste, sprouted beans.
Potato and other tubers
- Chips: wash, peel, slice thin, fry or bake, add salt.
- Starch: grate, wash with water, let the white starch settle, then dry it. Starch thickens soups and sauces.
- Dried and flour forms: cassava and sweet potato are dried or milled to last longer.
Tubers hold a lot of water, so they spoil fast unless dried, fried or chilled.
Vegetables and fruit
Fruit and vegetables are full of water, so they spoil quickly. Processing keeps them longer.
- Jam: fruit is cooked with sugar (about equal weight) and a little acid until it sets. Sugar holds water, so microbes cannot grow.
- Pickle: pieces are kept in salt, oil and spice or in vinegar. Salt and acid stop spoilage.
- Juice: fruit is crushed, pressed, filtered, heated and bottled.
- Drying: slices are dried in sun or hot air.
- Freezing: vegetables are briefly scalded (blanched) to stop enzymes, then frozen.
Hot-filling and sealing the jar while it is still hot, then letting it cool, makes a vacuum that keeps air and microbes out.
Livestock products
Milk
- Cool the milk soon after milking.
- Pasteurise: heat to about 72 °C for 15 seconds, then cool fast. This kills harmful germs.
- Add a culture of friendly lactic acid bacteria and keep warm: milk sets into curd (dahi, yogurt).
- Add acid or rennet to split milk into curd lumps and whey: this is how paneer and cheese start. Press and age the lumps for cheese.
Meat and eggs
- Meat is chilled, cut, then salted, smoked, cooked or frozen (sausage, ham).
- Eggs are washed, graded, and kept cool, or pasteurised as liquid egg.
These foods carry harmful bacteria easily, so cold storage and clean tools are a must.
Fermented foods
Fermentation is when friendly microbes eat sugar or starch and make acid, gas or alcohol. This changes taste and often helps keep the food.
| Food | Microbe | What happens |
|---|---|---|
| Bread, idli, dosa | Yeast and bacteria | Gas bubbles make the dough or batter rise |
| Curd, yogurt, cheese | Lactic acid bacteria | Milk sugar becomes acid, milk sets |
| Miso, soy sauce | Koji mould, yeast, bacteria | Mould breaks soy protein and starch into tasty parts; weeks to months of waiting |
| Kimchi, sauerkraut, pickles | Lactic acid bacteria | Salted vegetables turn sour and last longer |
| Vinegar | Yeast, then acetic bacteria | Sugar to alcohol to acid |
What the maker controls
- Temperature: each microbe has a best range.
- Salt: keeps bad microbes out while good ones grow.
- Time: short for curd (hours), long for miso (months).
- Clean tools: so wrong microbes do not join.
Try it: the curd test
Make two small bowls of lukewarm milk with a spoon of curd in each. Keep one at room temperature and one in the fridge. Next day the warm bowl is curd and the cold one is not. Microbes work fast when warm and slowly when cold. This is why fermentation needs a controlled temperature.
Key formulas and definitions
- Food line: raw material → clean → change → control → pack → product
- Pasteurisation of milk: about 72 °C for 15 seconds, then cool fast
- Jam: fruit and sugar about 1 : 1 by weight, cooked until it sets
- Flour yield (extraction %) = flour weight ÷ grain weight × 100
- Curd needs lactic acid bacteria + warmth (about 35–40 °C) + hours
- Fermentation: sugar → acid, gas or alcohol (made by microbes)
Worked examples
1. Why is milk heated to 72 °C before it is made into curd or cheese?
The heat kills harmful germs that may be in raw milk. Then only the friendly bacteria we add will grow, so the product is safe and always turns out the same.
2. 100 kg of wheat gives 75 kg of white flour. What is the flour extraction rate?
Extraction = flour ÷ grain × 100 = 75 ÷ 100 × 100 = 75 %. The other 25 kg is mostly bran and germ.
3. Why does jam last for months even though it is made from fresh fruit?
Jam has a lot of sugar, which holds on to water so microbes cannot use it. The jar is also filled hot and sealed, which keeps new microbes out.
4. Soy milk is warm and thin. What makes it turn into solid tofu?
A setting agent such as a mineral salt or an acid makes the proteins stick together into clumps. Pressing out the water gives a firm block.
5. A baker uses 500 g flour and 60 % water by flour weight. How much water?
60 % of 500 g = 0.6 × 500 = 300 g (300 mL) of water.
Common mistakes
- Thinking pasteurised milk is sterile. It kills harmful germs but still needs a fridge because some microbes survive.
- Believing fermented food is rotten. Fermentation is controlled and uses friendly microbes; spoilage is uncontrolled and uses harmful ones.
- Mixing up whole-wheat and white flour. Whole-wheat keeps bran and germ; white flour is mainly the starchy middle.
- Forgetting hygiene. The best recipe still makes unsafe food with dirty hands, tools or water.