Soaking: Beans, Rice, and Everything Dried

Soaking is not cooking; it is adding water

The outside and inside of a dried ingredient hold very different amounts of water. Boil it straight away and the outside overcooks while the centre stays dry. Soaking removes that gradient in advance, so its purpose is not to shorten cooking but to make it even.

Skip it and you usually get a blown-out exterior around a hard core.

The rule about salt is wrong

It is widely repeated that you must not salt the soaking water for beans. In fact the opposite is true: beans soaked in salted water (1 tsp per litre) soften better.

The reason is pectin in the skins. Pectin binds calcium and magnesium and stiffens; sodium displaces them, and the skin softens. For the same reason, beans cook poorly in hard water.

What genuinely must stay out is acid. Vinegar, tomato and lemon set pectin firm. So in bean dishes the tomato goes in after the beans are tender — which is exactly the order chana masala and dal use.

Beans that never soften

Sometimes they stay hard no matter how long you boil. Usually the beans are old: in storage the pectin in the skins cross-links permanently, and nothing reverses it. A date left on the bag is no guarantee.

A pinch of bicarbonate of soda (1/4 tsp per litre) breaks pectin down with alkalinity and does soften them. But it dulls the colour, destroys vitamins and can taste soapy, so treat it as an emergency measure.

When to discard the soaking water, and when to use it

This is the part that needs judgement.

Discard:

• Beans and pulses — the indigestible oligosaccharides leach into it.
• Dried chillies, where bitterness and grit come out of the seeds and pith. Grinding the vindaloo paste in vinegar alone is partly about not using that water.
• Anything gritty: wood ear or seaweed gets a final rinse.

Use:

• Dried shiitake. That water is a large share of the savouriness; throwing it out throws out half the aroma (building umami).
• Dried shrimp and shellfish, for the same reason.
• Sun-dried tomatoes, kombu.

With mushroom water, let the grit settle and pour off the top.

Rice depends on what it is for

• For steaming: 30 minutes evens out the moisture so the grains cook uniformly (cooking rice).
• For grinding: batters like dosa need 5-6 hours, since the grain has to be soft enough to grind.
• For fried rice the problem is the opposite — that is a question of cold cooked rice, not soaking.

Rough times

• Split lentils: 30 minutes, or none
• Chickpeas, soybeans: 8 hours or overnight
• Black beans, adzuki: 6-8 hours
• Dried shiitake: 30 minutes in warm water, 2 hours in cold
• Dried chillies: 15-20 minutes in hot water
• Rice for steaming: 30 minutes
• Rice for grinding: 5-6 hours
• Dried wood ear: 20 minutes

Hot water shortens the time but costs flavour. Use it only when rushed. Anything over 8 hours at summer room temperature starts to ferment, so long soaks are safer in the fridge.