The way to use baking soda when boiling dried legumes is to add a very small amount — around a quarter teaspoon per half kilo of legumes — to the soaking or boiling water. Baking soda shifts the water's acid-base balance slightly and breaks down the legume's tough skin structure, letting it soften in less time.
This method is mainly used for thick-skinned legumes like chickpeas, dried beans and borlotti beans; it's usually not needed for vegetables or softer legumes.
How does baking soda shorten cooking time?
A legume's outer skin is held together by a structure called pectin; in acidic or neutral water this breaks down slowly. In water that turns slightly alkaline, pectin breaks down faster, which softens the skin and lets water reach the interior more easily.
In practice this can noticeably shorten a boil that would normally take 1.5-2 hours; but the effect levels off as the amount of soda increases, and too much causes other problems.
How much is the right amount?
Less than a quarter teaspoon is usually enough for half a kilo of dried legumes, added either to the soaking water or at the start of boiling. Even for larger batches, the amount should scale proportionally rather than being added by eye.
Some cooks use baking soda only during the soaking stage and skip adding it to the boiling water — a more cautious approach that reduces its effect on flavour even further.
What happens if you use too much baking soda?
Adding more baking soda than recommended can leave a legume soft on the outside while still hard inside, and its texture can turn slick and mushy. Too much soda can also mask the legume's natural flavour and leave a faint soapy taste behind.
Long boiling in soda-treated water can also cause some loss of certain nutrients in the legume; this is why the amount should stay small and boiling shouldn't run longer than necessary.
Is baking soda necessary for every legume?
Thin-skinned legumes that already cook quickly, like red lentils, generally don't need baking soda. Thick-skinned legumes that require a long soak, like chickpeas and dried beans, are where baking soda is most often used, both to shorten cooking time and to get a softer texture.
For those who'd rather skip it, a longer soak and a pinch of salt in the boiling water can also help soften the skin, though the effect isn't as fast as baking soda's.
How can cooking time be shortened without baking soda?
For those who prefer not to use baking soda, the most effective alternative is a longer soak; soaking chickpeas or dried beans for 8-12 hours noticeably cuts down the boiling time. Changing the soaking water a couple of times also shortens cooking time and can mellow the legume's flavour a little.
Using a pressure cooker is another soda-free option; legumes cooked under pressure soften far faster than in a regular pot, giving a similar time-saving effect to what baking soda provides. The two approaches can also be combined; a legume that has already had a long soak cooks even faster in soda-treated water.