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.