Cooking legumes

Fresh shell beans cook fairly quickly, in 10-30 min. Peas, lima beans, cranberry beans, and soybeans (edamame) are the legumes most commonly eaten fresh. Whole dried beans and peas take one to two hours to cook. Their larger size and water intake affect cooking time. Initially, water can only enter through the beans through the hilum, the little pore on the curved back of the bean. After 30-60 minutes, the seed coat has fully hydrated and expanded so that water flowing can pass across the entire seed coat surface, though the rate of flow is still limited.

The liquid in which legumes are cooked greatly affects both, the quality of the cooked beans and the time it takes to cook them. The greater the volume of cooking water, the more color, flavor, and nutrients are leached out of the beans, and the more they are diluted. Beans are best cooked in just enough water to soak up and to cook in.

Take into account the following:

• Boiling water speeds cooking, but damages seed coats and cause the beans to disintegrate.
• Temperatures below boiling (180-200 degrees F/80-93 degrees C) are gentler and better maintain bean structure.  
• Hard water with high levels of calcium or magnesium reinforces the bean cell walls, so cooking takes longer and may prevent the beans from softening fully.
• Acidity slows the dissolving of the cell wall pectins and hemicelluloses, so it slows the softening process but it helps maintain structure.
• Alkalinity does the reverse; it enhances the softening process.
• Sugar reinforces cell-wall structure and slows the swelling of the starch granules. It also helps maintain structure.
• Salt in the water slows the rate at which the beans absorb water, but it does get absorbed eventually. If beans are pre-soaked in salted water, they cook much faster.
• High altitude lowers the boiling point, so cooking dry beans is prolonged.

Note: ingredients such as molasses, which are somewhat acidic and rich in sugar and calcium, and acidic tomatoes can preserve bean structure during long cooking and reheating, such as in baked beans.