By Harold McGee
Most mature legume seeds are starchy, and require cooking in water to soften the cotyledon cell walls and starch granules. Fresh shell beans are mature but still moist, and so cook fairly quickly, in 10 to 30 minutes. They’re also sweeter than the dried beans. Peas, lima beans, cranberry beans, and soybeans (edamame) are the legumes most commonly eaten fresh.
Whole dried beans and peas can take an hour or two to cook, much longer than the dried grains. This is due in part to their larger size, but also to the effectiveness of their seed coat at controlling the absorption of water, which is necessary for softening the cell walls and starch. Initially water can enter only through the hilum, the little pore on the curved back of the bean. After 30–60 minutes in cool water (more quickly in hot), the seed coat has become fully hydrated and expanded. From this point on, most of the water flowing into the bean passes across the entire seed coat surface, but the rate of flow is still limited. Legumes whose hulls have been removed—split peas, many Indian dals—cook more quickly and disintegrate into a mush.