Rehydrating dried pulses: the soak, and what it costs in water
Dried pulses are the best value in the store cupboard by a distance: years of shelf life, no refrigeration, excellent protein and fibre, and pennies a portion. They are also the ingredient most often got wrong, in two different ways — undercooked so they are unpleasant or worse, and planned without accounting for the water they need.
This page is about the soak. If you are cooking red kidney beans or other PHA-bearing pulses, read the kidney bean page first — that is a toxin question and it has a hard rule attached. This page is the general technique that sits underneath it.
The standard method, and why it does not transfer
The official soak, from NCHFP:
Place dried beans or peas in a large pot and cover with water. Soak 12 to 18 hours in a cool place.
Note the phrase “in a cool place”. It is not decoration. A pot of starchy water held at room temperature for the best part of a day is a growth medium, which is why the domestic version of this advice usually says to soak in the fridge.
Neither a cool larder nor a fridge is available in a van in July. So the overnight soak — the method everybody knows — is the one that transfers worst to the situation this site is about.
The hot soak, which does transfer
Both sources give a faster method that starts with boiling, and it is the one to use on the road. From USDA WIC Works:
For each pound of dry beans, add 10 cups of hot water; heat to boiling and let boil 2 to 3 minutes. Remove from heat, cover and set aside for up to 4 hours.
NCHFP’s version is tighter still:
Cover sorted and washed beans with boiling water in a saucepan. Boil 2 minutes, remove from heat, soak 1 hour and drain.
Three reasons this is the better method away from mains:
- It starts with a boil, so the water and the beans begin hot and sterile rather than sitting cool for eighteen hours.
- One to four hours, not overnight. You can start it after lunch and cook in the evening, rather than committing the night before.
- USDA notes the hot soak “helps reduce intestinal gas” — which, in a small shared space, is not a trivial benefit.
The trade is a few minutes of fuel at the start. Given that you are going to boil them anyway, it is close to free.
Throw the soaking water away
NCHFP, after either method: “Drain water.”
This is the step people skip to save washing up or to keep “the flavour”. Drain it. It carries the oligosaccharides that cause the digestive trouble, and for PHA-bearing beans it carries something considerably worse. Cook in fresh water.
Then actually cook them
Soaking is rehydration, not cooking. NCHFP:
Cover beans soaked by either method with fresh water and boil 30 minutes.
That is the figure for preparing beans for canning, and as a floor for ordinary cooking it is a sound one — then simmer on until genuinely tender. “Tender” means yielding completely when squashed against the roof of your mouth, not “softened”. Undercooked pulses are unpleasant, hard to digest, and in the case of the PHA-bearing ones the undercooking is the hazard itself.
Two things that stop beans softening, worth knowing before you blame the method:
- Age. Dried beans do not spoil, but they do get harder to cook. A bag of unknown vintage from the back of a locker may simply never soften. This is a real argument for rotating pulses through rather than treating them as permanent stock.
- Salt and acid added early. Add them once the beans are tender, not at the start.
What this costs in water
This is the part trip planning misses. Ten cups of water per pound of dry beans is roughly 2.4 litres per 450 g — and that is the soak alone, before the fresh water you cook in.
Dried pulses do not save weight. They move it from food to water. A tin of beans weighs about 400 g and needs nothing; the dried equivalent weighs far less in the bag and then demands several litres, plus the fuel to boil them twice.
Which way that comes out depends entirely on your water situation:
- Water is carried, trip is short — tins usually win outright. No soak, no long boil, no planning.
- Water is available and refillable, trip is long — dried pulses win comfortably. The bag weight is trivial and the water is free at the tap.
- Water must be sourced and treated — dried pulses are expensive in a way that is easy to miss, because every litre now costs fuel or filter life. See water treatment.
The general rule: dried pulses are a good deal exactly when water is cheap. Work out which situation you are in before you buy for the trip rather than after.
Lentils and split peas are the exception
Red lentils, split peas and other split or small pulses need no soak at all. They cook from dry in twenty to thirty minutes, use far less water, and carry none of the PHA problem that whole beans do.
For one-burner cooking away from a tap they are the most practical dried pulse by some margin, and the fact that dal is one of the best things you can cook out of a cupboard is not a coincidence.