Vol. V · The Molecules of Food Plate 1 of 11food composition, water, carbohydrate, protein, fat, ash, macronutrientsM

Water, Carbohydrate, Protein, Fat.

Four families of molecules make up nearly all of every food. Learn what heat does to each and most of cooking follows.

Read the composition of any food and four numbers dominate: water, carbohydrate (sugars, starch and fibre), protein and fat; minerals, the "ash", are a percent or two. Their proportions vary enormously — cucumber is nearly all water, butter four-fifths fat, sugar all carbohydrate — and so does what heat does to them. Water boils and carries heat (Vol. III). Proteins unfold and set (Vol. VI). Starch swells and thickens; sugars caramelise (Vol. VII). Fats melt, carry flavour and fry (Vol. IX).

So a food's composition is already a forecast of how it will cook. Meat is water and protein: it firms and loses juice. Rice and flour are starch: they need water and heat to soften. Peanuts and butter are fat: they melt and brown. The workshop shows the composition of common foods from the USDA tables.

Below: grams of water, carbohydrate, protein, fat and ash in 100 g of each food (USDA FoodData Central), and the food you choose in detail.

What you will learn
Workshop
Composition per 100 g (USDA FoodData Central, SR Legacy). Carbohydrate is "by difference" and includes fibre.

Composition is a forecast

A sirloin steak is 66 % water, 20 % protein and 13 % fat, with almost no carbohydrate: cooking it is about setting protein without squeezing out too much water. An egg is 76 % water and 13 % protein — protein chemistry again, with fat in the yolk. Flour is only 12 % water and 76 % carbohydrate: before it can cook it must take up water, and its starch must gelatinise.

The families also interact. Water dissolves sugars and salts and carries heat; fat carries flavours that do not dissolve in water (XI.8); proteins and sugars together brown (Vol. VIII). Most of the rest of Part Two takes one family at a time and asks what heat, acid, salt and time do to it.

Food composition tables began with Wilbur Atwater's analyses for the U.S. Department of Agriculture in the 1890s; the USDA's FoodData Central is their descendant, and this course takes its numbers from it.

Terms

Macronutrients
Protein, fat and carbohydrate: the families that supply energy.
Carbohydrate by difference
What is left of 100 g after water, protein, fat and ash are measured; includes sugars, starch and fibre.
Ash
The mineral residue left after burning a food.
Composition table
Measured amounts of each component per 100 g of a food.
Food is mostly water, carbohydrate, protein and fat; the mix forecasts how it will cook.

Sources

  1. USDA FoodData Central, SR Legacy (April 2018), public domain.
  2. Atwater general factors: 4 kcal/g protein, 9 kcal/g fat, 4 kcal/g carbohydrate (USDA, Energy Value of Foods, Agriculture Handbook 74, 1955/1973).