What food is made of
Food science uses chemistry, biology and physics to understand food. Main nutrients:
- Carbohydrates (starch, sugars, fibre): main energy source. Starch is a long chain of glucose units.
- Proteins: chains of amino acids folded into shapes; they build and repair the body.
- Fats and oils: concentrated energy (about 37 kJ per gram, compared with about 17 kJ for carbohydrate or protein).
- Water, vitamins and minerals: needed in small amounts for body processes.
Human needs depend on age and activity. Different farming methods (intensive, organic, mixed) and processing affect yield, cost, nutrients and the environment. Feeding about 8 billion people means balancing enough food, good nutrition and low pollution.
Culinary transformations: what heat does
Protein denaturation
Heat (about 60–80 °C), acid or beating unfolds proteins. Unfolded chains join and trap water, so egg sets, paneer forms when acid is added to hot milk, and meat firms up. Over-cooking squeezes out water and makes food rubbery.
Starch gelatinisation
In hot water (about 60–70 °C) starch grains absorb water and swell, so rice softens and flour thickens gravy. When cooled, starch slowly firms again (retrogradation): bread goes stale.
Browning
Above about 140 °C in dry heat, amino acids and sugars react: the Maillard reaction gives flavour and brown colour (toast, roasted coffee, tandoor bread). Caramelisation is sugar alone breaking down above about 160 °C. Boiling keeps food near 100 °C, so boiled food does not brown.
Choosing a method
Boiling and steaming are gentle; frying and roasting reach higher temperatures. Some vitamins (C, some B vitamins) dissolve in water or break down with heat, so short cooking with little water keeps more of them. Fats form an emulsion with water when an emulsifier is present (mayonnaise uses egg yolk).
Fermentation
Fermentation is when microbes break down sugars with little or no oxygen to get energy.
- Alcoholic fermentation by yeast: glucose → ethanol + carbon dioxide (C6H12O6 → 2C2H5OH + 2CO2). The CO2 makes bread dough rise; the ethanol bakes off.
- Lactic acid fermentation by bacteria: glucose → lactic acid. The acid lowers pH, sets milk proteins into curd and yoghurt, and preserves pickles, sauerkraut and kimchi.
Fermentation improves taste, texture, keeping time and sometimes digestibility. Temperature control matters: too cold is slow, too hot kills the microbes.
Processing, preservation and food safety chemistry
Processing turns raw farm produce into food that is safe, lasts longer and is easy to use: milling, pasteurisation, canning, drying, freezing, packaging.
- Microbes grow fastest in the danger zone, about 5–60 °C. Refrigeration (below 5 °C) slows them; cooking (core 75 °C) or pasteurisation (milk at 72 °C for 15 s) kills most.
- Removing water (drying, adding salt or sugar) and lowering pH (vinegar, lactic acid) stop microbes.
- Additives such as preservatives, antioxidants and emulsifiers are tested and allowed only up to safe limits.
- Food safety chemistry also checks for contaminants (pesticide residues, heavy metals) and adulteration.
Food trades (bakers, cooks, dairy and quality-control workers) use this science every day, and a cold chain keeps food safe during distribution.
Try it at home
Mix a little yeast and sugar in warm water in a bottle and stretch a balloon over the mouth. Make a second bottle with cold water. After 30 minutes, which balloon grew? Then check the free-play step of the 3D: what temperature range did the microbes like?
Key formulas and definitions
- Glucose → ethanol + CO₂ (yeast, alcoholic fermentation).
- Glucose → lactic acid (bacteria, lactic fermentation).
- Denaturation: heat, acid or beating unfolds proteins (≈60–80 °C).
- Gelatinisation: starch + water + heat (≈60–70 °C) → swollen, thick.
- Maillard: amino acids + reducing sugars, dry heat ≈140 °C+ → brown flavours.
- Caramelisation: sugar alone ≈160 °C+.
- Danger zone: ≈5–60 °C; keep cold below 5 °C, hot above 60 °C.
Worked examples
1. Why does a boiled potato not turn brown but a roasted one does?
Step 1: water boils at 100 °C, so boiled food stays near 100 °C. Step 2: Maillard browning needs about 140 °C or more and dry surfaces. Step 3: in an oven the surface dries and gets hotter, so it browns.
2. A cook adds lemon juice to hot milk. What happens and why?
The acid lowers the pH and denatures milk proteins (casein), which clump into solid paneer and leave liquid whey.
3. Dough with yeast rises in a warm kitchen but hardly at all in a fridge. Explain.
Yeast ferments sugar to make CO₂. Its enzymes work fastest in warmth (about 25–35 °C) and very slowly in the cold, so less gas forms in the fridge.
4. 180 g of glucose is fully fermented by yeast. What mass of CO₂ forms? (C₆H₁₂O₆ = 180 g/mol, CO₂ = 44 g/mol)
Step 1: 180 g = 1 mol glucose. Step 2: 1 mol glucose → 2 mol CO₂. Step 3: 2 × 44 = 88 g of CO₂.
Common mistakes
- Thinking browning is just burning. Maillard browning makes new flavour molecules; burning (charring) is much hotter and bitter.
- Thinking cold kills microbes. A fridge only slows them; they grow again when warm.
- Saying all fermentation makes alcohol. Lactic acid fermentation (curd, pickles) makes acid, not alcohol.
- Thinking denatured protein is 'destroyed' and useless. Its shape changes, but the amino acids are still digested and used.