Vol. I · What Cooking Does Plate 1 of 10why cook, heat, proteins, starch, safety, flavour, temperature and timeMSF

Why We Cook.

Cooking is applied chemistry: a chosen amount of heat, for a chosen time, to make particular molecules change and others stay as they are.

A raw egg and a boiled one contain the same molecules in the same amounts. What changed is their arrangement: the long protein chains of the white, folded tightly in the raw egg, have unfolded in the heat and tangled into a solid net that holds water. Every cooking method does something like this to some part of the food — proteins set, starch swells and softens, cell walls loosen, sugars and amino acids react into brown, savoury compounds, and bacteria die.

What makes cooking a skill rather than a recipe is that these changes happen at different temperatures and at different speeds. The protein that makes a steak firm sets at a lower temperature than the one that makes it dry; rice starch needs more heat than wheat starch; browning needs a surface far hotter than boiling water can give. The workshop below holds a piece of food at one temperature for a time you choose and shows which changes have happened.

Below: eight changes that cooking makes, each as the fraction completed after the time you set at the temperature you set, and the number of ten-fold reductions of Salmonella in the same time.

What you will learn

Name the main things heat does to food: proteins set, starch gelatinises, cell walls soften, browning, and microbes die.
See that each change has its own temperature range.
Explain why time matters as much as temperature.
Connect cooking to safety, digestibility and flavour.

Workshop

Fraction of each change completed after holding the food at the chosen temperature for the chosen time (course kinetics, midpoints from calorimetry studies cited in the sources). Right: ten-fold reductions of Salmonella in the same time (log-linear model fitted to the USDA FSIS beef table).

Different changes, different temperatures

Held at 65 °C for ten minutes, the muscle protein myosin is 100% set and the egg-white protein ovotransferrin 100%, but ovalbumin, the other main egg-white protein, is only 1% set, and rice starch 27% gelatinised. That one temperature makes a firm, moist piece of chicken and a soft, barely set egg white — and leaves rice hard. At 55 °C only 2 of the eight changes pass halfway; at 75 °C 7; at 95 °C 8. Cooking is choosing which ones you want.

Safety follows the same logic. Ten minutes at 65 °C gives 45.2 ten-fold reductions of Salmonella, far more than the seven that food-safety tables ask for; ten minutes at 55 °C gives only 0.7. But thirty minutes at 60 °C gives 17.3: time can stand in for temperature. That trade — lower heat for longer — runs through the whole course, from sous vide (XVI.7) to the safety tables of Vol. XII.

At the stove

Boil three eggs for 6, 9 and 12 minutes, cool them in cold water and cut them open side by side. The white sets before the yolk because ovotransferrin sets at a lower temperature than the yolk proteins — and because heat reaches the white first.

Use eggs straight from the fridge, lower them gently into water already at a full boil, and keep it boiling.

Anthropologists have argued that cooking shaped human evolution: cooked food yields more energy for less chewing and digestion, which may have allowed larger brains and smaller guts (Richard Wrangham, Catching Fire, 2009). The idea is debated; plate XXXIV.1 weighs the evidence.

Terms

Denaturation: A protein unfolding from its natural shape, usually by heat, acid, salt or beating.
Gelatinisation: Starch granules absorbing water and swelling when heated, which thickens and softens.
Maillard reaction: Reactions between sugars and amino acids that brown food and create savoury, roasted flavours.
Log reduction: A ten-fold fall in the number of living microbes; seven log reductions leave one in ten million.

Cooking is choosing which chemical changes happen: each has its own temperature, and time can partly replace temperature.

Sources

Differential scanning calorimetry of muscle: myosin denatures around 54–58 °C, collagen shrinks around 60–67 °C, actin around 70–80 °C (A. Wright, I. B. Leach and P. Wilding, "Differential scanning calorimetric studies of muscle and its constituent proteins", J. Sci. Food Agric. 28, 1977; H. McGee, On Food and Cooking, 2004). The course uses midpoints within these ranges.
Egg proteins: ovotransferrin sets near 62 °C, ovalbumin near 80 °C, the yolk thickens near 65 °C and sets near 70 °C (H. McGee, On Food and Cooking, 2004, ch. 2; P. Barham, The Science of Cooking, 2001).
Starch gelatinisation ranges measured by DSC: wheat about 52–64 °C, potato 58–66 °C, maize 62–72 °C, rice 68–78 °C, tapioca 59–70 °C (S. Damodaran and K. L. Parkin (eds.), Fennema's Food Chemistry, 5th ed., 2017, ch. 3). The course uses the midpoints.
USDA FSIS, Appendix A to the Compliance Guidelines for Meeting Lethality Performance Standards for Certain Meat and Poultry Products (time–temperature table for 6.5- and 7-log reductions of Salmonella in cooked beef).