Vol. VII · Starches and Sugars Plate 4 of 11rice, water ratio, absorption method, gelatinisation, lid, resting, moistureMHT

Why Rice Cooks the Way It Does.

Perfect rice is arithmetic: the grains must end at about two-thirds water, and every gram of water either goes into them or out as steam.

Raw white rice is about 12 % water; cooked rice about 65–70 %. To get there, each grain must absorb a little more than its own weight of water and reach the temperature at which its starch gelatinises (VII.1) all the way through. In the absorption method — the standard in Chinese, Japanese and most home kitchens — rice and a measured amount of water are brought to the boil, covered, and cooked until the water is gone, then left to rest.

The arithmetic is simple. Water goes either into the rice or out of the pot as steam. A tight lid keeps evaporation small, so less water is needed; an open pot or a long cook loses more. The rest, off the heat with the lid on, lets the water that is left in the outer layers move into the centres of the grains. The workshop computes how wet the cooked rice will be.

Below: the water content of cooked rice from the ratio of water to rice you choose and the share of water lost as steam, against the range that cooks find right for each kind of rice.

What you will learn
Workshop
Water balance: cooked rice moisture = (water in the raw rice + water added − water evaporated) ÷ (raw rice + water added − water evaporated). Raw white rice 11.6 % water (USDA). The band is about 62–70 %, from firm long-grain to soft short-grain.

A water budget

With a tight lid losing about a tenth of the water, a water-to-rice ratio of about 1.78 by weight gives cooked rice of 66 % water — firm-tender, separate grains; an open pot losing 30 % needs about 2.28. Rice cookers seal well, which is why their markings use less water than stove-top recipes. Long-grain rices are usually cooked a little drier, short-grain and Japanese rice a little wetter and stickier, and older or brown rice needs more water and time because its bran or hard grain slows the water.

Washing removes surface starch so grains stay separate (Japanese rice is washed until the water runs nearly clear); soaking for half an hour lets water in before heat and gives evener cooking. Resting ten minutes with the lid on finishes the job: the outer layers, wetter than the centres, pass water inward, and the grains firm slightly as they cool. Lifting the lid too soon lets the steam that should be finishing the grains escape.

At the stove

Weigh 200 g of rice and 300 g of water (ratio 1.5), cook covered on a low heat until the water is gone (about 15 minutes), rest ten minutes, then weigh the pot's contents and taste. Adjust the ratio by 0.1 next time if it is too firm or too soft.

Cooks in China and Japan often measure rice water with a finger: the water should stand about one knuckle above the levelled rice — a rule that works because it adds a fixed depth of water above the grains, roughly scaling with the pot.

Terms

Absorption method
Cooking rice in just the water it will absorb, covered, until the water is gone.
Water-to-rice ratio
Weight (or volume) of water per weight (or volume) of rice.
Resting
Leaving cooked rice covered off the heat so moisture evens out.
Washing
Rinsing raw rice to remove surface starch.
Cooked rice is about two-thirds water: add what the grains will hold plus what the steam will take, and rest it covered.

Sources

  1. USDA FoodData Central, SR Legacy (April 2018), public domain.
  2. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.