One instruction covering several different intentions
Soak the pulses overnight. Soak the rice for twenty minutes. Soak the poppy seeds in hot water. Soak the tamarind. Soak the almonds and peel them. The same verb is used for all of it, and each instruction’s reasoning is different enough that following one rule for everything produces poor results in at least half the cases. The word doesn’t tell you what you’re trying to achieve.
Underneath the various instructions there are three distinct things water can do to a dry ingredient, and any given soak may be aiming at one, two or all three of them.
Getting water in, which is slower than it looks
A dry seed has to take on a great deal of water before it can cook, and heat alone cannot substitute for that. Boiling a dry pulse means the outside hydrates and softens while the middle is still dry, so the surface breaks down long before the centre is ready, and the result is a pot of mush surrounding hard cores.
Water enters at different rates through different parts of a seed, and the seed coat is the main barrier. That is why whole pulses need long soaks and skinned split ones barely need any, and why an old seed that has been sitting in a warm cupboard soaks unevenly and stubbornly.
Rice is a milder version of the same problem. A short soak lets water into the grain before the heat arrives, which gives more even cooking and grains less likely to break, and it is one reason a soaked long-grain rice cooks up longer and more separate.
Getting substances out, which is the quieter half
Water going in also brings things out. Pulses contain a family of sugars that human digestion cannot break down, which pass through to be fermented further along with the results everyone complains about, and those sugars are water-soluble and leach out into the soaking water.
That is the argument for throwing the soaking water away, which is otherwise a strange instruction given how much people worry about losing nutrients. The same water carries out some of the compounds that bind minerals, and some of the tannins in a coloured seed coat that make a pulse taste astringent and cook slowly.
Not everything should be discarded, though. The water in which dried mushrooms, dried vegetables or tamarind have soaked carries flavour rather than problems, and pouring it away throws out the concentrated result of the drying. The distinction is whether the soak is removing something unwanted or extracting something wanted.
Waking the seed up
A seed that takes on water begins to behave like a seed preparing to germinate, and enzymes inside it start work. Over a long soak this breaks down some of the stored starch and protein into simpler forms, which changes the flavour slightly towards sweetness and makes the seed easier to cook and to digest.
The change is small over a normal overnight soak and larger over a day or two, which is why the effect is rarely noticed with pulses and very obvious with anything left long enough to show a shoot. Cooks who soak rice for a fermented batter are working with this too, since the microbes that will do the fermenting are being given water and a warm seed to start on.
Taken further, this is sprouting, which several Indian kitchens do deliberately with whole pulses. But it also means a soak that runs too long in warm weather goes somewhere unintended, since the same conditions suit bacteria and yeasts. A pulse soaking on a hot afternoon can begin to smell sour within hours, and that is fermentation rather than spoilage in the early stages, but it is not usually what the dish wanted.
The variables nobody mentions in the instruction
Water temperature changes everything. Warm water hydrates a great deal faster than cold, which is why the instruction for poppy seeds or for a hard nut usually specifies it, and why a soak that takes eight hours in winter takes four in summer.
The quantity of water is worth a thought as well. A seed that swells to two or three times its dry volume needs enough water above it to stay submerged throughout, and a soak that runs dry part way leaves the top layer half-hydrated. It is the most common reason a soaked batch still cooks unevenly.
Water composition matters too, since calcium and magnesium dissolved in hard water interact with the pectin in seed walls and slow softening down. And the age of the ingredient is the largest hidden variable of all: a pulse bought this month and one that has been in a shop for a year will not respond to the same soak, and no instruction written in a recipe can account for that. Judging by how the seed looks and feels after soaking is more reliable than the clock.
Common questions
Should I add salt or soda to the soaking water?
A little salt in the soak is generally helpful, since the ions weaken the pectin in the seed coat and speed softening, which contradicts the older advice to keep salt away entirely. Soda works faster and is harsher, damaging texture and some vitamins. Salt is the safer of the two and the difference is not dramatic either way.
Is soaking rice necessary?
Not necessary, but useful for long-grain varieties where even cooking and unbroken grains are the goal. It shortens the cooking, reduces breakage and helps the grains elongate rather than swell. For a rice that is meant to be soft and clinging, soaking works against what the dish wants.
How long is too long for pulses?
Once the seed has taken up as much water as it can, which is usually somewhere around eight to twelve hours for a whole pulse in cool conditions, further soaking adds nothing and starts to risk fermentation. In warm weather the sensible answer is to soak in the refrigerator or to change the water part way through.
Editor, Wah Taste
Sanaya has written about everyday cooking, street food, spice & pantry for most of the last decade and prefers a plain explanation to a clever one.
