Working Characteristics of Commodities

Why Commodities Behave Differently in the Kitchen

Pick up a raw egg and a hard-boiled one — they feel and behave completely differently, yet the only thing that changed was heat. This is the heart of food science: every commodity has working characteristics that determine what happens when you cook with it. Understanding these characteristics explains why a sponge cake rises, why a sauce thickens, why a stir-fry browns — and crucially, why things can go wrong.

Carbohydrates: Gelatinisation and Dextrinization

Gelatinisation is what turns a thin liquid into a thick sauce. When a roux-based béchamel sauce is heated on the hob, the starch granules in the flour absorb water, swell and eventually burst, releasing amylose chains that tangle together and thicken the sauce. The process is essentially complete above 80 °C. If the sauce is not stirred during this stage, clumps of gelatinised starch form — the lumpy white sauce so familiar from school kitchens. Stirring distributes the heat evenly and keeps the granules from aggregating.

Dextrinization happens when starch is dry-heated. Toast the surface of a slice of bread under the grill and you will see dextrinization at work: the starch molecules on the surface break down into shorter chains (dextrins), producing the golden-brown colour and slightly crisp texture of toast. This is a different reaction from gelatinisation, which requires water. Dextrinization also contributes to the crust of a baked loaf and the croutons in a salad.

Fats: Shortening, Aeration, Plasticity and Emulsification

Fats are among the most functionally versatile commodities. Shortening describes the way fat coats flour particles and prevents gluten strands from forming long networks — this is exactly what you want in shortcrust pastry, where the goal is a crumbly, tender texture rather than chew. Aeration occurs when fat (butter or margarine) is creamed vigorously with sugar: the mechanical action forces air into the fat, creating tiny bubbles that expand in the oven and contribute to a light sponge. Plasticity refers to the ability of solid fats to be spread, rolled or moulded at room temperature — important for laminated pastries such as croissants, where butter must be rolled into layers without melting. Emulsification is the ability to hold oil and water together. Egg yolk contains lecithin, a natural emulsifier, which is why adding egg yolk to a vinaigrette produces a temporarily stable suspension, and why hollandaise sauce can hold butter in a water-based liquid without separating.

Proteins: Coagulation, Foam Formation, Gluten Formation and Denaturation

Coagulation is the reason scrambled eggs solidify when heated: liquid egg protein denatures and then bonds together, forming a solid curd. In a quiche filling, the protein in the egg-and-milk mixture sets in the oven, encasing the other ingredients. A related property is foam formation: whisking egg whites stretches and denatures the protein, which wraps around tiny air bubbles and stabilises them — giving a meringue mixture its volume. The foam collapses if fat is accidentally introduced (a trace of egg yolk, a greasy bowl), because fat destroys the protein film around the air bubbles.

Gluten formation occurs in wheat-flour doughs. Glutenin and gliadin proteins in flour absorb water and, when the dough is kneaded, align and bond into a continuous elastic network. This network traps carbon dioxide produced by yeast fermentation, causing the dough to rise. Over-working a pastry dough activates the same protein network, producing a tough, chewy result instead of a short, crumbly one — which is why pastry-making guides say “handle the dough as little as possible.”

Fruit and Vegetables: Enzymic Browning and Oxidisation

Enzymic browning is why a freshly sliced apple turns brown within minutes of being cut. The cut surface exposes phenolic compounds to polyphenol oxidase enzymes; these react with oxygen from the air to produce brown melanin pigments. In cooking, enzymic browning can be prevented by: covering the cut surface with acidulated water (vitamin C from lemon juice lowers pH, inhibiting the enzyme); blanching (brief boiling denatures the enzyme); or vacuum packing (removing oxygen). In the production of black tea, enzymic browning is deliberately encouraged to develop colour and flavour. Oxidisation is the broader term for nutrient loss (particularly vitamin C) when fruit and vegetables are cut, stored or cooked — oxygen in the air, heat and water all accelerate the process.

Dry vs Moist Methods of Cooking

The cooking method determines which of a commodity’s working characteristics are activated. Dry methods include roasting, baking, grilling, frying and dry-frying. In dry methods, surface moisture evaporates quickly, temperatures at the surface can reach well above 100 °C, and reactions like dextrinization, the Maillard reaction, and fat rendering take place. A Sunday roast chicken in the oven is a showcase for dry-heat cooking: the proteins denature and coagulate in the breast, fat renders from the skin, and the Maillard reaction creates the brown crust and rich flavour. Moist methods include boiling, steaming, poaching, braising and stewing. Water limits temperatures to 100 °C at atmospheric pressure; this prevents surface browning but can cause water-soluble vitamins (B vitamins, vitamin C) to leach into the cooking water. Steaming is preferable to boiling for retaining micronutrients in vegetables.