The golden crust of a breaded pork cutlet, a set egg white, fluffy yeast dough, sour pickles and smooth mayonnaise — behind each of them are specific chemical reactions and laws of physics. Fry a cutlet, boil an egg to the minute, ferment pickles, whisk up mayonnaise and boil water on Rysy, Poland's highest peak.
Temperature speeds up reactions, water holds the surface at 100 °C, acid protects against spoilage, and proteins change shape.
Simplified model: the browning rate rises with temperature according to the Arrhenius equation, and as long as the surface is wet, its temperature stays not much above 100 °C.
Reducing sugars (glucose, fructose, lactose) combine with the amino groups of amino acids and proteins. This sets off a chain of hundreds of reactions that produces brown melanoidins and aromas: pyrazines (nutty, roasted), furans, thiazoles (meaty) and Strecker aldehydes. It runs slowly even at lower temperatures, but speeds up markedly above about 140 °C.
Caramel needs no amino acids. Sucrose softens and breaks down from about 160 °C (fructose caramelizes earlier): first you get a pale, straw-colored syrup, then at about 170–180 °C an amber caramel with the aroma of maltol, furans and diacetyl (the smell of butter). Above about 190–200 °C the caramel quickly turns bitter and then chars — leaving mostly black carbon.
As long as there is water on the surface, the energy goes into evaporating it and the temperature stays close to 100 °C — the meat turns gray and “stews”. That's why meat boiled in water never browns. Dried and placed in a well-heated pan, it passes 140 °C sooner. Don't overcrowd the pan — the juices that run out will cool it down.
Acrylamide forms mainly in starchy foods (fries, chips, heavily toasted bread) — just fry and bake to “golden, not brown”.
Model: the egg as a sphere of radius 21.5 mm (yolk 15.5 mm), heat conduction and irreversible protein denaturation with Arrhenius kinetics. Real eggs vary in size, so the times are approximate.
During long cooking, the sulfur-containing amino acids of egg-white proteins (cysteine) release hydrogen sulfide H₂S. The gas travels to the cooler yolk and reacts with iron(II) ions — a gray-green layer of iron(II) sulfide FeS forms at the boundary. It's harmless but spoils the look and the taste. The fix: don't cook longer than needed, and cool the eggs in cold water right away.
The white of a fresh egg has a pH of about 7.6–8. CO₂ escapes through the shell, and after a few days the pH rises to about 9. At lower pH the white is thought to stick more firmly to the membrane under the shell — hence the advice to hard-boil eggs that are a few days old. Putting the eggs straight into boiling water also helps.
Egg-white foam holds together thanks to proteins that unfold at the air–water boundary and form springy bubble walls. Fat (even a drop of yolk) gets in their way, while sugar thickens the water and stabilizes the meringue.
Simplified model: yeast activity depends on temperature (fastest at about 35 °C; it stops above about 50 °C and dies from about 55 °C), and the better the dough is kneaded, the more gas the gluten holds.
Yeast (Saccharomyces cerevisiae) is a living single-celled fungus. In dough it breaks sugars down into ethanol and CO₂ — the gas inflates the bubbles, and the alcohol almost completely evaporates in the oven.
½ teaspoon of baking soda is about 2.3 g. Baking powder contains soda, an acidic salt (e.g. disodium pyrophosphate) and starch, which keeps it dry — the acid comes built in.
Sourdough is a mix of wild yeasts and lactic acid bacteria. The bacteria produce lactic and acetic acid, so the pH of the starter drops to about 3.5–4.3. The acid gives sourdough bread its characteristic taste, and in rye dough it helps produce a good crumb.
Baker's ammonia (ammonium bicarbonate) breaks down entirely into gases in the oven — it leaves no residue. It's used for thin, dry bakes such as pierniki (Polish gingerbread) and ammonia cookies, from which the ammonia has time to escape.
Simplified model: three groups of bacteria grow depending on temperature, salt and pH; lactic acid bacteria turn the sugars in the vegetables into lactic acid, and the pH is calculated from the balance between the acid and the vegetables' natural buffer. Real ferments vary.
Microbes need free water. Sugar in jam and salt in cured meat bind water, and drying removes it — aw drops and microbes can't multiply.
Curing, salted herring, jams and preserves. Low-sugar jam spoils faster — keep it in the fridge.
Smoke contains antimicrobial compounds (e.g. phenols), and drying lowers aw. Dried mushrooms have an aw below 0.6.
In the fridge (up to about 5 °C) bacteria grow very slowly, and in the freezer (−18 °C) not at all — but they don't die.
Louis Pasteur showed that brief heating kills most microbes. Milk is pasteurized, for example, at 72 °C for 15 s.
Canning in a boiling-water bath (100 °C) is enough for acidic preserves (jams, pickles in vinegar, ferments), but it doesn't destroy the spores of the botulism bacterium in low-acid vegetables (green beans, peas, mushrooms, meat) — these need acidifying or the higher temperature of a pressure cooker. Throw out a jar with a bulging lid without tasting it.
In the bowl: an egg yolk, a teaspoon of mustard and a tablespoon of lemon juice. Goal: blend in 200 mL of oil.
Simplified model: whisking breaks free oil into droplets, and the thicker the emulsion already is, the faster it does so. Too much free oil at once, or too little water (oil fraction above about 92%) — and the emulsion splits.
Milk is an “oil-in-water” emulsion (O/W): fat globules wrapped in a membrane of proteins and phospholipids float in water. Butter is the reverse — “water-in-oil” (W/O): about 82% fat, with water droplets trapped between fat crystals.
Whipped cream (30–36% fat) is a foam: partly crystallized fat globules stick together on the surfaces of the bubbles and hold them up like scaffolding. That's why the cream has to be cold. Whipped too long, it turns into butter and buttermilk.
Split mayonnaise can be rescued: take a fresh yolk and whisk the split mixture into it drop by drop.
Pressure comes from the standard atmosphere model (on a real day it differs by a few percent), and the boiling point from the Clausius–Clapeyron equation. Potatoes are assumed to cook in about 20 min at 100 °C, and the change in that time is estimated with the rough rule “2× faster for every 10 °C”.
Model: a 14 cm flame heats the center of the bottom, heat spreads out radially (conductivity λ), and the bottom gives it off to the air. Typical thicknesses: copper 2.5 mm, aluminum 4 mm, cast iron 5 mm, steel 2 mm. Good steel pans have a “sandwich” base with an aluminum layer.
The magnetron produces waves at a frequency of 2.45 GHz (wavelength about 12 cm). The alternating electric field swings the dipoles of water molecules back and forth, and the friction between them produces heat. This is non-ionizing radiation — a photon's energy is about 0.00001 eV, a million times too little to change atoms. Food does not become radioactive.
A standing wave forms in the cavity, creating cold and hot spots — that's why the plate turns. Ice heats up poorly because its molecules can't rotate freely.
Under the glass is a coil carrying alternating current at a frequency of tens of kilohertz. Its changing magnetic field induces eddy currents in the bottom of the pot, which heat the pot itself — the cooktop stays relatively cool. The bottom must be ferromagnetic (steel, cast iron); plain aluminum or copper won't work.
Without a lid, hot steam escapes and carries away a lot of energy (about 2.26 kJ for every gram). With a lid, the water boils sooner and you use less gas or electricity.
30 g of salt per liter raises the boiling point by only about 0.5 °C. We salt pasta water for flavor, not for temperature.
The rate of almost every reaction in the kitchen rises exponentially with temperature. The Arrhenius equation describes this: the higher the activation energy Ea, the more sharply a reaction “switches on” above a certain temperature. That's why a few degrees decide whether the yolk is runny, and whether the cutlet is golden or burnt.
A protein is a long chain of amino acids folded into a precise shape. Heat, acid, salt or whipping break the weak bonds that hold this shape — this is denaturation. The unfolded chains link up into a network that traps water: that's how egg white sets.
180 g of glucose gives 92 g of ethanol and 88 g of CO₂, and 1 g of baking soda with acid gives about 0.29 liters of CO₂ (at 25 °C). In the oven the gas expands further, and water evaporates.
Water boils when its vapor pressure equals the surrounding pressure. On Rysy (2,499 m) the pressure is about 750 hPa and water boils at about 92 °C; on Mount Everest, at about 70 °C. In a pressure cooker at about 2 bar — at about 120 °C.
Simplifications: the models on this page capture the direction and order of magnitude of the effects, but they are not recipes. Real foods differ in composition, size and moisture.