What purpose does putting a strip of seaweed in the pot when cooking dried beans serve?
Some sources claim that dried kombu (a kelp used extensively in Japanese cuisine, primarily for making dashi stock) neutralizes difficult-to-digest small carbohydrates in beans—not a theory we planned on evaluating in the test kitchen! But we hazarded a guess that the seaweed could also act as a flavor enhancer. Kombu, after all, is one of the richest sources of glutamates and nucleotides, which together produce an amplified umami taste. Our taste tests showed that kombu not only boosts bean flavor but also improves texture: Pinto beans soaked and then cooked in water with a strip of kombu had soft skins and smooth interiors; soaked beans cooked in water alone were more grainy and tough.
Our favorite bean-cooking method calls for overnight brining; the sodium in the salt solution replaces some of the calcium and magnesium in the bean skins, making them more permeable and resulting in more tender beans inside and out. Kombu works in a similar fashion, its sodium and potassium ions trading places with minerals in the beans to create a smoother, creamier consistency. But we also found that kombu eliminates the need for the overnight soak; dried beans that went directly into the pot with the seaweed were nearly as tender as those that had been soaked in plain water or even brined.
We still prefer brining beans because we always have salt on hand, but if you’re the last-minute type, you might consider stocking dried kombu (available at Asian markets and natural foods stores) in your pantry. In 4 quarts of water, simmer 1 pound of beans, 1 tablespoon of salt (for seasoning), and one 3 by 5-inch strip of kombu until the beans are tender.