Dried legumes are soaked because the water lost during drying needs to go back into the grain before it can cook quickly and evenly. Chickpeas or dried beans cooked without soaking can turn soft on the outside while staying hard in the middle, since water reaches the centre far more slowly during cooking.
Soaking also cuts the cooking time roughly in half: chickpeas soaked overnight cook in about 45 to 60 minutes, while unsoaked chickpeas can take 2 to 3 hours.
What does soaking actually change inside the grain?
Dried legumes are stored at a very low moisture level; soaking lets the starch layer swell as it absorbs water and softens the outer skin. That swelling lets heat reach the grain more evenly during cooking, so it cooks through its whole volume rather than only from the outside in.
In an unsoaked grain, the outer skin stays tough, so by the time the heat reaches the centre, the outer layer has often overcooked and started to break apart.
How long, and in what kind of water, should you soak them?
Chickpeas and dried beans are usually left in room-temperature water for 8 to 12 hours, essentially overnight; in hot weather, soaking in the fridge avoids fermentation. Use at least twice the volume of water to grain, since the grain can swell to roughly double its size as it soaks.
The soaking water is then poured off and the grain rinsed in fresh water, which clears away some of the compounds that collect in that water.
Which legumes can cook without soaking at all?
Split, small-grained legumes like red and yellow lentils cook in 15 to 20 minutes even without soaking, since removing the husk already makes it easier for water to reach the grain. For types that keep a thicker skin, like green lentils or borlotti beans, skipping the soak noticeably extends the cooking time.
What can you do if you forget to soak in time?
If you forget to soak in time, you can do a quick version by covering the grain in boiling water and letting it sit, covered, for about an hour; it doesn't fully replace an overnight soak but softens the grain somewhat. A pressure cooker is another practical shortcut for unsoaked legumes, though the grain may still cook less evenly than a properly soaked one.