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The science of cooking

The mechanisms underneath what you see happening — grouped by the processes that belong together.

What starch does when it is heated

Thickening, setting and going stale are four stages of one process, and the order matters.

  • Crisping

    A dried surface layer becomes rigid and brittle enough to fracture audibly under bite.

  • Crust formation

    A dried, structurally distinct outer layer forms once the surface loses free water faster than the interior can resupply it.

  • Gelation

    A continuous network forms through a liquid and holds it, turning a pourable system into one that keeps its shape.

  • Microbial spoilage

    Bacteria, yeasts and moulds growing in a food and changing it until it is no longer wanted: souring, softening, sliming, visible growth, off odours.

  • Moisture equilibration and loss of crispness

    Moisture moves from the wet interior into the dry crust until the two equalise, and the crust softens.

  • Staling

    The firming and drying of baked goods over time, driven largely by retrogradation and by moisture redistribution rather than by moisture loss alone.

  • Starch gelatinisation

    Heating starch in the presence of water destroys the ordered structure of the granule irreversibly, and the granule swells and takes up water.

  • Starch granule swelling

    Granules take up water and expand, which is what thickens a sauce before anything ruptures.

  • Starch pasting

    Swollen granules crowd and rupture, releasing polymer into the surrounding water and building viscosity.

  • Starch retrogradation

    After gelatinisation, starch polymers slowly re-associate into ordered regions on cooling and standing.

Why food browns

The Maillard reaction and caramelisation are not the same thing. Here is where each one applies.

  • Caramelisation

    Thermal degradation of sugars alone, with no amino compound involved, producing colour and its own distinct aroma set.

  • Maillard reaction

    A reaction between reducing sugars and amino compounds that produces brown pigments and a large family of aroma compounds.

  • Melanoidin formation

    The late stage of non-enzymatic browning, where large brown nitrogen-containing polymers form and give the colour its depth.

  • Non-enzymatic browning

    The family of browning reactions that proceed without enzymes, of which the Maillard reaction and caramelisation are the two principal members.

How vegetables soften

Cooked soft and gone limp are different failures with different causes.

  • Cell-wall breakdown

    Plant cell walls lose integrity with heat, and the tissue softens as cells stop holding together.

  • Pectin solubilisation

    Pectin in the middle lamella dissolves with heat, weakening the adhesion between neighbouring cells.

  • Turgor loss

    The pressure of water inside a cell against its wall is what makes a leaf stand up and a stem snap.

Other transformations

Changes that happen in food without belonging to any one family — heat, time, air and water, each working on its own terms.

  • Aeration

    Gas is incorporated and stabilised within a structure, lowering density and changing mouthfeel.

  • Alcoholic fermentation

    Yeasts convert sugars principally to ethanol and carbon dioxide.

  • Anthocyanin pH response

    Anthocyanin pigments change colour with pH, shifting between red, purple and blue-green ranges.

  • Carryover cooking

    Heat already stored in the outer layers keeps moving inward after the food leaves the heat, so the centre continues to rise.

  • Cell rupture on cutting

    Cutting, peeling, grating and mashing break open cells that were keeping enzymes and their substrates apart.

  • Chlorophyll degradation

    Heat and acid convert bright green chlorophyll into duller olive-brown compounds.

  • Collagen conversion to gelatin

    Connective tissue collagen, given heat and moisture, solubilises into gelatin, turning a tough structure into a rich, yielding one.

  • Condensation

    Vapour meeting a cooler surface returns to liquid there, releasing its latent heat and wetting the surface.

  • Crowding suppresses evaporation

    Too much food in a pan releases more vapour than can leave, so the surrounding air saturates and the surface stays wet enough to stall browning.

  • Egg protein setting

    Egg proteins denature and set over distinct, relatively narrow temperature bands, and the bands differ between white and yolk.

  • Emulsion breakage

    Heat, shear or a shift in the emulsifier lets dispersed droplets coalesce, and the phases separate.

  • Enzymatic browning

    Enzymes in damaged plant tissue oxidise phenolic compounds to brown pigments, needing no heat at all.

  • Enzymatic tenderisation

    Enzymes break down protein structure over time, softening texture without heat.

  • Ethylene-driven senescence

    Ethylene is a gas the produce itself gives off, and it is the signal that accelerates its own decline — and its neighbours’.

  • Evaporation

    Liquid water leaving a surface as vapour, driven by the difference between the surface and the surrounding air.

  • Evaporative cooling

    Water leaving a surface as vapour takes a large amount of energy with it, holding the surface near the boiling point while any free moisture remains.

  • Fat as an aroma carrier

    Many aroma compounds are fat-soluble, so fat both extracts them and releases them slowly, lengthening how long a flavour is perceived.

  • Fat crystallisation on cooling

    Cooling fat forms crystals whose size and form set the final texture, and the cooling path decides which form appears.

  • Fat melting

    Solid fat becomes liquid over a range rather than at a point, because it is a mixture of triglycerides with different melting behaviour.

  • Fat rendering

    Heat breaks down fat-holding tissue and releases the fat as a liquid, leaving the remaining solids to brown.

  • Gas expansion

    Trapped gases and vapour expand on heating, lifting and opening a structure before it sets.

  • Gluten development

    Hydrated wheat proteins align and cross-link under mechanical work into an elastic, gas-retaining network.

  • Gluten relaxation

    Left alone, a worked gluten network loses elastic tension and becomes extensible again.

  • Heat penetration

    Heat entering a food does not arrive everywhere at once; it advances inward from the surface, and everything about timing follows from how fast that front moves.

  • Heat recovery after a cold load

    Cold food entering a hot medium drops the medium temperature; how fast it comes back decides whether the surface ever develops.

  • Ice crystal growth

    How large the ice in frozen food grows, which is decided by how fast it froze rather than by how cold it ended up.

  • Internal steam generation

    Water inside the food turns to vapour and expands enormously, lifting structures, splitting surfaces and driving liquid outward.

  • Lactic fermentation

    Lactic acid bacteria convert sugars principally to lactic acid, lowering pH and changing flavour and texture.

  • Moisture migration

    Water moves through food along gradients of concentration, pressure and temperature, from wetter to drier and from hotter to cooler.

  • Myofibrillar contraction

    Muscle proteins shorten as they denature, first across the fibres and then along them, squeezing the structure.

  • Myoglobin colour states

    The colour of meat tracks the chemical state of myoglobin, which changes with heat and with exposure to oxygen.

  • Osmotic moisture movement

    Dissolved salt or sugar outside a cell draws water across the membrane, and the direction reverses once the gradient does.

  • Protein coagulation

    Unfolded proteins bond to one another into a network, turning a liquid into a solid or a soft structure into a firm one.

  • Resting and redistribution

    During rest the gradient flattens and expelled liquid is partly reabsorbed as the structure relaxes.

  • Shrinkage

    Food loses volume as water leaves and structures contract.

  • Starch release and gluey texture

    Working starch-rich food after gelatinisation frees long polymer chains into the liquid and produces a gluey, elastic texture.

  • Surface drying

    The surface loses free water faster than the interior can replace it, which is the precondition for the surface temperature to rise past the boiling point.

  • Surface-area-to-volume ratio

    The proportion of a piece that is surface governs how much browning, drying and heat uptake it gets relative to its mass.

  • Surface-to-core temperature gradient

    The difference between the outside and the middle.

  • Syneresis

    A set gel contracts and expels the liquid it was holding, appearing as weeping.

  • Thermal mass

    How much energy a body must absorb or give up to change temperature.

  • Thermal protein denaturation

    Heat unfolds proteins from their folded shape, exposing regions that were buried and changing how they interact.

  • Thickness effect on cooking time

    Time to heat the centre grows far faster than thickness does, because the distance heat must travel and the mass to be heated both increase.

  • Volatile generation

    Cooking creates aroma compounds that were not present in the raw material.

  • Volatile loss

    Aroma compounds are lost to the air during cooking, which is why long-cooked food smells strongest in the kitchen and least on the plate.

  • Water activity

    How available the water in a food is, rather than how much there is.

Other explanations

Why food behaves as it does, where the explanation stands on its own.

  • Acetic fermentation

    How acetic acid bacteria turn alcohol into vinegar, why the process needs air, and what it means for kombucha, vinegar and sour ferments.

  • Ice crystals and texture

    Why frozen food leaks when it thaws, how crystal size governs the damage, and why some foods survive freezing and others do not.

  • Mould fermentation

    How deliberately cultivated moulds transform food, what enzymes they contribute, and how the good ones differ from the ones on your bread.

  • Salt in fermentation

    Why salt is the central control in a vegetable ferment, what it does to microbes and to texture, and why the quantity is not a flavour decision.

  • Yeast fermentation

    What yeast does to sugar, why it makes bread rise and drinks alcoholic, and what controls how fast and how far it goes.