What do I need to know about soaking and cooking dried beans?

Through the years, we’ve waffled back and forth about the best way to cook dried beans. Admittedly, we haven’t been consistent: some recipes specify that the beans be soaked before cooking, others do not. Our recommendation? Follow the recipe. Each has been specifically developed for soaked or unsoaked beans and should be prepared accordingly.

Soaking Water

So that being said, for recipes that do soak the beans, we typically recommend a long soak—eight hours to overnight. Quick soaking, or bringing the beans to a boil and allowing them to sit for an hour or two before draining and proceeding with the recipe, works fine at rehydrating the beans, though it can rob the beans of some of their nutritional value (see below).

In recent testing, we’ve found that soaking dried beans in mineral-rich; hard tap water can toughen their skins. Some recipes recommend using distilled water to avoid this issue, but we’ve discovered a simpler solution: adding salt to the tap water, which prevents the magnesium and calcium in the water from binding to the cell walls, and it will also displace some of the minerals that occur naturally in the skins. We found that three tablespoons of salt per gallon of soaking water is enough to guarantee soft skins.

Storing Soaked Beans

If you happen to soak beans and aren’t able to use them immediately, they can be drained, transferred to a zipper-lock bag, and refrigerated for up to four days before being used without ill affect to flavor or texture. We do warn against soaking beans much beyond 24 hours as testing has suggested that they can lose flavor and develop tough skins and a mealy texture.

Does Soaking Beans Affect Nutrition?

Soaking dried beans is necessary for hydration, which accelerates the cooking process. While both slow and quick bean-soaking techniques exist, testing has proven that the heated water used with the quicker methods increases the solubility of water-soluble nutrients, such as calcium, magnesium, thiamine, riboflavin, and niacin. Also, the heat of boiling water breaks down cell membranes within the beans, which speeds the release of water-soluble nutrients. For these reasons, quick soaking tends to leach somewhat more of the nutrients out of the beans than do slow soaking methods.

Foaming Beans

Simmering beans typically produce a frothy cap of foam. It’s innocuous stuff that’s nothing more than tiny pockets of air surrounded by a thin layer of water that are stabilized by proteins exuded from the beans that dissolve in the water. While they won’t harm the beans, we typically skim the foam off for a clearer appearance.

Eliminating Gas from Beans

For some, the greatest obstacle to preparing beans is not the lack of a good recipe but an aversion to the discomfort associated with digestion. The creation of unwanted intestinal gas begins with the arrival of small chains of carbohydrates (called oligosaccharides) into the large intestine. People cannot digest these molecules efficiently, but bacteria residing at the end of the gut do and produce gas as a byproduct. Some sources say that presoaking or precooking beans alleviates gas production by removing these carbohydrates. Our science editor decided to put these theories to the test by measuring the amount of one of the most prevalent small carbohydrates in black beans, stachyose.

His results gave the theories some credence. Beans soaked overnight in water and then cooked and drained showed a 28 percent reduction in stachyose. The precooking, quick-soak, method, consisting of a one-minute boil followed by a soak for an hour, was more effective, removing 42.5 percent of the stachyose. While we have reservations about the quick-soaking method, it might be the best way to prepare your beans if they cause you significant discomfort.

Troubleshooting Hard Beans

Finally, if you’ve cooked your beans for hours and found they failed to soften, chances are they are either old and stale (and will never fully hydrate or soften), the water is too hard, or there’s a acidic element present. Food scientists universally agree that high acidity can interfere with the softening of the cellulose-based bean cells, causing them to remain hard no matter how long they cook. Alkalinity, on the other hand, has the opposite effect on legumes. Alkalines make the bean starches more soluble and thus cause the beans to cook faster. (Older bean recipes often included a pinch of baking soda for its alkalinity, but because baking soda has been shown to destroy valuable nutrients, few contemporary recipes suggest this shortcut.)

But how much acid is too much acid? At what pH level is there a negative impact on the beans? We cooked four batches of small white beans in water altered with vinegar to reach pH levels of 3, 5, 7, and 9. We brought them to a boil, reduced the heat to a low simmer, and tested the beans every 30 minutes for texture and doneness. The beans cooked at a pH of 3 (the most acidic) remained crunchy and tough-skinned despite being allowed to cook 30 minutes longer than the other three batches. The beans cooked at pHs of 5, 7, and 9 showed few differences, although the 9 pH batch finished a few minutes ahead of the 7 pH batch and about 20 minutes ahead of the 5 pH batch. Acidity, then, must be relatively high to have any significant impact on beans. So in real world terms, season with discretion and don’t add a whole bottle of vinegar or wine to your beans until they are tender.