The captious vegetarian

There’s always controversy surrounding beans. Myths and superstition abound

Soaking Beans

The number one issue of debate when cooking beans is whether they have to be soaked first, and if so for how long. There are a number of issues that must be considered when deciding whether to soak your beans:

1. effect on cooking time (and hence energy usage)
2. effect on complex carbohydrates that cause flatulence
3. effect on beneficial nutrients
4. effect on flavor and texture

Cooking time: Regarding how soaking affects cooking times, I read a very scientific analysis recently, and I think it was in Mark Bittman’s “how to cook everything” book. Does anyone have the book and can verify? I think his conclusion was that soaking is unnecessary, that it only reduces the cooking time by about 30 minutes (for a long soak) and 15 minutes for a short soak. And since a quick soak takes an hour you’re actually losing time rather than gaining time. However, if you think of it the night before then soaking them can’t hurt, and will reduce energy usage slightly. What really affects cooking times the most is how fresh your beans are. If the beans are really old then they might take many, many hours to cook, even if they were pre-soaked.

Flatulence: Beans are rich in fiber and complex sugars called alpha-galactosides which humans cannot digest.  Bacteria in the intestines digest these complex sugars, producing carbon dioxide.  The two primary alpha-galactosides in beans are raffinose and stachyose. Cook’s Illustrated analyzed how soaking affects stachyose. They found that a long soak led to a 28% reduction in stachyose, and a quick-soak (1 minute boil, 1 hour soak) removed 42.5% of stachyose. Thus, they argue that if you have intestinal discomfort issues from beans then soaking and tossing the soaking liquid will help. However, it seems to me that if you’re making a dish that doesn’t call for the bean broth (like a bean salad), then soaking is unnecessary since you’re going to toss the liquid in the end anyhow. I suppose it’s possible that the stachyose gets reabsorbed during the cooking process, in which case a quick soak would be preferable, but that seems unlikely to me.  Other sources online claim that even if three quick soaks are used, and 90% of the complex sugars are removed, beans will still cause flatulence in many people due to their high fiber content. In addition, the beans suffer in terms of texture and flavor.  The best strategy to reduce gas seems to be to eat lots of beans and other high fiber foods.  Eventually the micro-flora in your gut adapt in some way so that less gas is produced.  (I don’t understand how though. Can anyone explain what chemical changes actually take place?)

Nutritional content: Cook’s Illustrated also studied how soaking affects beneficial nutrients. They say that during soaking many nutrients leach out of the beans, more so with a quick soak (presumably due to the brief heat) than with a long cold soak. Apparently heat breaks down cell membranes within the beans, and increases the solubility of water-soluble nutrients, such as calcium, magnesium, thiamine, riboflavin, and niacin. As a result, quick soaking tends to leach somewhat more of the nutrients out of the beans than do slow soaking methods. Again, however, if you either retain the soaking liquid or discard the bean cooking broth it seems irrelevant which soaking method you choose. In the latter case, presumably the same quantity of water soluble nutrients (if not more) would be leached out of the beans when you cook them. The only situation in which the soaking strategy would matter, it seems to me, is if you discard the soaking liquid, but use the bean cooking broth in your recipe. In that case, you should use a cold, slow soak to maximize nutritional content.

Flavor and texture: Cook’s Illustrated claims that quick-soaking beans has a negative effect on the texture. Since I never soak my beans, I can’t really say either way. They also say that soaking beans for too long results in beans with tough skins, mealy interiors, and a lack of flavor. More specifically, they soaked black beans in the fridge overnight. They used one batch immediately, drained a second batch and left it in a ziplock bag for three days, and left a third batch soaking for three days. The first and second batches made excellent black beans soup. Both batches of beans were tender, moist, and creamy and had a rich, full-bodied broth. The third batch, resulted in a soup that was thin and bland, and the beans were too firm with tough skins. Now, presumably they threw out the soaking water. I wonder what would have happened if they retained the soaking water for the soup?

Adding Salt and Acids to Beans

Another controversial issue is whether adding salt or acids to beans slows down the cooking time, or toughens beans. Cook’s Illustrated did a study with lentils and concluded that salt has no effect on cooking time or bean texture.  Furthermore, they suggest that for maximum flavor it’s actually essential to salt your beans at the beginning rather than the end of of cooking. From personal experience with many other types of beans I’ve determined that this advice holds for all types of beans, not just lentils. Also, when soaking beans Cook’s Illustrated says that by using salt water the bean will cook up with softer and more pliable skins. Apparently the salt displaces some of the minerals like calcium and magnesium in the bean skins, which tends to make the skins tough. Since salt ions are weaker than mineral irons, they allow more water to penetrate into the skins, leading to a softer texture. Apparently during soaking the salt doesn’t make it all the way to the center of the beans, so the largest effect is on the outer skin. Cook’s Illustrated recommends 3 Tbs. of salt per gallon of soaking water. I imagine that cooking the beans in salted water has a similar, if lesser effect, since less salt is used.
Cook’s Illustrated says that acid does slow down the cooking process, but that the cooking liquid has to be pretty acidic to have a noticeable effect, so adding a few Tbs. of vinegar or tomato paste won’t interfere in any way, but cooking your beans in pure tomato sauce might be slightly detrimental.  I found other posts saying that calcium and sugar also slow down the softening rate of beans, so blackstrap molasses should be added towards the end of cooking when making baked beans, but I haven’t confirmed this.
Other Issues

Both Paula Wolfert and Harold McGee says that “less is more” when it comes to the amount of cooking water used to cook beans. McGee says the the beans will actually absorb more water when cooked in a smaller volume of water. Apparently, less cooking water means fewer carbohydrates are leached out, and these carbohydrates absorb a lot of water which then can’t be absorbed by the beans. It doesn’t quite make sense to me, but I think I have seen some evidence of this in my own bean cooking experiences.

How does cooking affect the nutritional content of beans. A nutritionist interviewed by Cook’s Illustrated says: “More than 70 percent of bean nutrients are retained during cooking, including 86 percent of the protein, 83 percent of the iron, 96 percent of the zinc, 66 percent of the niacin, and 70 percent of the thiamine. About 53 percent of the calcium content, however, is lost. These numbers take into account that nutrient concentration diminishes during cooking because the beans take on moisture. For instance, one cup of dry kidney beans containing 44 grams of protein expands during soaking and cooking to two and one-half cups containing 38 grams of protein.”