Lima bean, b.u.t.ter bean

Phaseolus lunatus Phaseolus lunatus

Tepary bean

Phaseolus acutifolius Phaseolus acutifolius

Runner bean

Phaseolus coccineus Phaseolus coccineus

Peanut

Arachis hypogaea Arachis hypogaea

The seed coat is interrupted only at the hilum, the small depression where the seed has been attached to the pod, and where it will absorb water once it's in the ground or the pot. The seed coat may be fairly thin, as in the peanut, but is as much as 15% by weight of the chickpea and 30% of the lupin. The legume seed coat is almost entirely cell-wall carbohydrates, and includes most of the seed's indigestible fiber. The coats of colorful varieties - pinks, reds, black - are rich in anthocyanin pigments and related phenolic compounds, and therefore in antioxidant power.

Most beans and peas are mainly protein and starch (see box, p. 489). The major exceptions are soybeans and peanuts, which are around 25% and 50% oil respectively. Many legumes are several percent sucrose by weight, and noticeably sweet.

Some legume seeds are rich in defensive secondary compounds (p. 258), notably protease inhibitors, lectins, and in the case of tropical lima beans, cyanide-generating compounds (American and European lima varieties generate little or no cyanide). Animals fed a diet of raw beans will actually lose lose weight. All of these potentially toxic compounds are disabled or removed by cooking. weight. All of these potentially toxic compounds are disabled or removed by cooking.

Seed Colors The colors of beans and peas are determined mainly by anthocyanin pigments in the seed coat. Solid reds and blacks generally survive cooking, while mottled patterns become washed out when the water-soluble pigments leak into adjacent nonpigmented areas and into the cooking water. The intensity of color is best maintained by minimizing the amount of cooking water; start the beans in just enough water to cover, and add water only as needed to keep them barely covered. Persistently green peas and dried beans owe their color to chlorophyll. The colors of beans and peas are determined mainly by anthocyanin pigments in the seed coat. Solid reds and blacks generally survive cooking, while mottled patterns become washed out when the water-soluble pigments leak into adjacent nonpigmented areas and into the cooking water. The intensity of color is best maintained by minimizing the amount of cooking water; start the beans in just enough water to cover, and add water only as needed to keep them barely covered. Persistently green peas and dried beans owe their color to chlorophyll.

Pale beans with translucent seed coats sometimes develop a delicate pink color in the small embryonic stem when they're cooked. This is probably a result of the same reaction that causes the reddening of poached quinces and pears (p. 281).

Legumes and Health: The Intriguing Soybean Beans and peas are generally excellent sources of a number of nutrients, including protein, iron, various B vitamins, folic acid, and starch or oil. Varieties with colored seed coats provide valuable antioxidants. Among all the legumes, however, soybeans appear to have unusual potential for affecting human health. Epidemiological studies have shown that countries in which soybeans are a staple food, notably China and j.a.pan, have significantly lower rates of heart disease and cancer. It may be that soybeans are part of the explanation.

The anatomy of a legume seed. A side view with one of the two cotyledons removed to show the embryo. The hilum is a small pore through which water can pa.s.s directly to the embryo; it and the seed coat control the rate at which dry beans and peas absorb water and soften during cooking.

It turns out that soybeans contain storage forms of several phenolic compounds called isoflavones, isoflavones, which are liberated by the action of our intestinal bacteria as active compounds (genistein, daidzein, and glycitein) that resemble the human hormone estrogen. The active forms are therefore referred to as "phytoestrogens" (from the Greek which are liberated by the action of our intestinal bacteria as active compounds (genistein, daidzein, and glycitein) that resemble the human hormone estrogen. The active forms are therefore referred to as "phytoestrogens" (from the Greek phyton, phyton, "leaf"). Mung beans and other legumes also contain isoflavones, but in much smaller quant.i.ties. (Of commonly eaten soy foods, the boiled whole beans contain by far the greatest concentration of isoflavones, about double the amount found in tofu.) Phytoestrogens do appear to have hormone-like and other effects on the human body. There's evidence that they may slow bone loss and the development of prostate cancer and heart disease. However, some studies suggest that phytoestrogens can worsen preexisting breast cancer, and are protective against some cancers only when consumed during adolescence. Our understanding of phytoestrogens is still very incomplete. It's too early to say whether soybeans are more beneficial to human health than any other seed, or whether it's a good idea to eat them often. "leaf"). Mung beans and other legumes also contain isoflavones, but in much smaller quant.i.ties. (Of commonly eaten soy foods, the boiled whole beans contain by far the greatest concentration of isoflavones, about double the amount found in tofu.) Phytoestrogens do appear to have hormone-like and other effects on the human body. There's evidence that they may slow bone loss and the development of prostate cancer and heart disease. However, some studies suggest that phytoestrogens can worsen preexisting breast cancer, and are protective against some cancers only when consumed during adolescence. Our understanding of phytoestrogens is still very incomplete. It's too early to say whether soybeans are more beneficial to human health than any other seed, or whether it's a good idea to eat them often.

Saponins are soap-like defensive compounds that have a water-soluble end and a fat-soluble end, so they can act as emulsifiers and foam stabilizers. They're one of the reasons that a pot of soybeans boils over so readily! Soybeans are a rich source of saponins, which may make up 5% of their total weight, about half of which is in the hulls. Some plant saponins are so strong that they damage our cell membranes. Soy saponins are gentler, and bind to cholesterol so that the body can't absorb it efficiently. Soybeans are also a good source of phytosterols, chemical relatives of cholesterol that also interfere with our absorption of cholesterol and thus lower blood cholesterol levels. are soap-like defensive compounds that have a water-soluble end and a fat-soluble end, so they can act as emulsifiers and foam stabilizers. They're one of the reasons that a pot of soybeans boils over so readily! Soybeans are a rich source of saponins, which may make up 5% of their total weight, about half of which is in the hulls. Some plant saponins are so strong that they damage our cell membranes. Soy saponins are gentler, and bind to cholesterol so that the body can't absorb it efficiently. Soybeans are also a good source of phytosterols, chemical relatives of cholesterol that also interfere with our absorption of cholesterol and thus lower blood cholesterol levels.

The Problem of Legumes and Flatulence Several chemical const.i.tuents of beans are responsible for an uncomfortable, sometimes embarra.s.sing consequence of eating legumes: the generation of gas in the digestive system.

The Cause: Indigestible Carbohydrates Everyone produces a mixture of gases from their intestine, about a quart a day, thanks to the growth and metabolism of our resident bacteria. Many legumes, especially soy, navy, and lima beans, cause a sudden increase in bacterial activity and gas production a few hours after they're consumed. This is because they contain large amounts of carbohydrates that human digestive enzymes can't convert into absorbable sugars. These carbohydrates therefore leave the upper intestine unchanged and enter the lower reaches, where our resident bacterial population does the job we are unable to do. Everyone produces a mixture of gases from their intestine, about a quart a day, thanks to the growth and metabolism of our resident bacteria. Many legumes, especially soy, navy, and lima beans, cause a sudden increase in bacterial activity and gas production a few hours after they're consumed. This is because they contain large amounts of carbohydrates that human digestive enzymes can't convert into absorbable sugars. These carbohydrates therefore leave the upper intestine unchanged and enter the lower reaches, where our resident bacterial population does the job we are unable to do.

One kind of troublesome carbohydrate is the oligosaccharides, oligosaccharides, molecules consisting of three, four, and five sugar molecules linked together in an unusual way. But the latest research suggests that the oligosaccharides are not the primary source of gas. The cell-wall cements generate just as much carbon dioxide and hydrogen as the oligosaccharides - and beans generally contain about twice as much of these carbohydrates as they do oligosaccharides. molecules consisting of three, four, and five sugar molecules linked together in an unusual way. But the latest research suggests that the oligosaccharides are not the primary source of gas. The cell-wall cements generate just as much carbon dioxide and hydrogen as the oligosaccharides - and beans generally contain about twice as much of these carbohydrates as they do oligosaccharides.

The Cures: Soaking, Long Cooking A commonly used method for reducing the ga.s.siness of beans is to boil them briefly in excess water, let them stand for an hour, then discard the soaking water and start the cooking with fresh water. This does leach out most of the water-soluble oligosaccharides - but it also leaches out significant quant.i.ties of water-soluble vitamins, minerals, simple sugars, and seed-coat pigments: that is, nutrients, flavor, color, and antioxidants. That's a high price to pay. An alternative is simple prolonged cooking, which helps by eventually breaking down much of the oligosaccharides and cell-wall cements into digestible single sugars. Oligosaccharides are also consumed by the bean during germination, and consumed by microbes during fermentation: so sprouts, miso, and soy sauce, as well as extracts like bean curd, are less offensive than whole beans. A commonly used method for reducing the ga.s.siness of beans is to boil them briefly in excess water, let them stand for an hour, then discard the soaking water and start the cooking with fresh water. This does leach out most of the water-soluble oligosaccharides - but it also leaches out significant quant.i.ties of water-soluble vitamins, minerals, simple sugars, and seed-coat pigments: that is, nutrients, flavor, color, and antioxidants. That's a high price to pay. An alternative is simple prolonged cooking, which helps by eventually breaking down much of the oligosaccharides and cell-wall cements into digestible single sugars. Oligosaccharides are also consumed by the bean during germination, and consumed by microbes during fermentation: so sprouts, miso, and soy sauce, as well as extracts like bean curd, are less offensive than whole beans.

Bean Flavor Beans owe their typical beany flavor to a large endowment of the enzyme lipoxygenase, which breaks unsaturated fatty acids into small, odorous molecules. The main components of beaniness are gra.s.sy hexa.n.a.l and hexanol and mushroomy octenol. Lipoxygenase gets its chance to act when the bean cells are damaged and there's enough moisture and oxygen available: for example, when fresh beans are bruised, or dried damaged beans are soaked or brought slowly to a boil. The strong beaniness of soybean products is generally accepted in Asia but objected to in the West, where food scientists have developed techniques to minimize it (see box, p. 494). The aroma of cooked beans also has a distinct sweet note, which comes from lactones, furans, and maltol.

Some beans may be warehoused for years before they find their way to supermarkets or into prepared foods. Prolonged storage causes legumes to lose some typical flavor notes and acc.u.mulate stale ones.

Bean Sprouts Bean sprouts are best known from the cooking of China, where mung bean sprouts became popular in the south and soybean sprouts in the north about 1,000 years ago. Many other legumes are sprouted in Asia and elsewhere, from the tiny alfalfa seed to the ma.s.sive fava bean. Cooks sometimes trim larger sprouts of their rootlets, primordial leaves, and dense cotyledons, so that the subtle texture and flavor of the stems can be enjoyed without distraction. Sprouts are generally cooked minimally if at all to preserve the delicate flavor and tender but crunchy texture.

Cooking Legumes Most mature legume seeds are starchy, and require cooking in water to soften the cotyledon cell walls and starch granules. Fresh sh.e.l.l beans are mature but still moist, and so cook fairly quickly, in 10 to 30 minutes. They're also sweeter than the dried beans. Peas, lima beans, cranberry beans, and soybeans (edamame) are the legumes most commonly eaten fresh.

Whole dried beans and peas can take an hour or two to cook, much longer than the dried grains. This is due in part to their larger size, but also to the effectiveness of their seed coat at controlling the absorption of water, which is necessary for softening the cell walls and starch. Initially water can enter only through the hilum, the little pore on the curved back of the bean. After 3060 minutes in cool water (more quickly in hot), the seed coat has become fully hydrated and expanded. From this point on, most of the water flowing into the bean pa.s.ses across the entire seed coat surface, but the rate of flow is still limited. Legumes whose hulls have been removed - split peas, many Indian dals dals - cook more quickly and disintegrate into a mush. - cook more quickly and disintegrate into a mush.

The Cooking Liquid The quality of cooked beans and the time it takes to cook them depend on the cooking liquid. In vegetable cooking, large volumes of vigorously boiling water minimize enzyme damage to vitamins and pigments by keeping the temperature high when the vegetables are added. Long-cooked legumes are a different story. The greater the volume of cooking water, the more color, flavor, and nutrients are leached out of the beans, and the more they're diluted. So these seeds are best cooked in just enough water for them to soak up The quality of cooked beans and the time it takes to cook them depend on the cooking liquid. In vegetable cooking, large volumes of vigorously boiling water minimize enzyme damage to vitamins and pigments by keeping the temperature high when the vegetables are added. Long-cooked legumes are a different story. The greater the volume of cooking water, the more color, flavor, and nutrients are leached out of the beans, and the more they're diluted. So these seeds are best cooked in just enough water for them to soak up and and to cook in. And though boiling temperatures speed cooking, the turbulence of boiling water can damage the seed coats and cause the beans to disintegrate; lower temperatures (180200F/8093C) are slower but gentler. to cook in. And though boiling temperatures speed cooking, the turbulence of boiling water can damage the seed coats and cause the beans to disintegrate; lower temperatures (180200F/8093C) are slower but gentler.

The cooking water's content of dissolved substances also affects cooking times and textures. Hard water with high levels of calcium or magnesium actually reinforces the bean cell walls (p. 282). It can therefore slow the softening of the beans or even prevent them from softening fully. Acidic cooking liquids slow the dissolving of cell-wall hemicelluloses and therefore the softening process, while alkaline cooking water has the reverse effect. Finally, many cooks and cookbooks say that adding salt to the cooking water prevents beans from softening. It does slow the rate at which they absorb water, but they do eventually absorb it and soften. And when beans are pre-soaked in salted water, they actually cook much faster (below).

Maintaining the Texture of Cooked Beans Three substances slow the softening of beans and therefore make it possible for the cook to simmer beans for hours or reheat them without disintegrating them. Three substances slow the softening of beans and therefore make it possible for the cook to simmer beans for hours or reheat them without disintegrating them. Acids Acids make the cell-wall hemicelluloses more stable and less dissolvable; make the cell-wall hemicelluloses more stable and less dissolvable; sugar sugar helps reinforce cell-wall structure and slows the swelling of the starch granules; and helps reinforce cell-wall structure and slows the swelling of the starch granules; and calcium calcium cross-links and reinforces cell-wall pectins. So such ingredients as mola.s.ses - somewhat acid and rich in both sugar and calcium - and acidic tomatoes can preserve bean structure during long cooking or reheating, as for example in baked beans. cross-links and reinforces cell-wall pectins. So such ingredients as mola.s.ses - somewhat acid and rich in both sugar and calcium - and acidic tomatoes can preserve bean structure during long cooking or reheating, as for example in baked beans.

Reducing Cooking Times by Presoaking Though beans are an ideal food for slow, easy cooking in a low oven, it's sometimes desirable to cook them faster. In mountainous areas, where high alt.i.tude lowers the boiling point, the cooking of dry beans can become an all-day affair. Though beans are an ideal food for slow, easy cooking in a low oven, it's sometimes desirable to cook them faster. In mountainous areas, where high alt.i.tude lowers the boiling point, the cooking of dry beans can become an all-day affair.

There are several different ways to reduce the cooking time of beans and peas. The simplest way is to soak dried beans in water before cooking them. This reduces cooking time by 25% or more, and for a very basic reason: heat penetrates a dry seed faster than water does. If beans are cooked directly from the dry state, much of the cooking time is actually spent waiting for water to get to the center. Meanwhile the outer portions of the bean cook more than they need to and may get undesirably fragile.

Briefly Fermented Legumes in IndiaThough India isn't as fond of fermented foods as many other countries, it did find ways of turning legume and rice gruels into slightly raised pancakes and steamed cakes. In the making of the cakes called idli, idli, cooked black gram and rice are ground and mixed to make a thick batter, then allowed to ferment overnight. The same lactic acid bacteria found in fermented milks and creams ( cooked black gram and rice are ground and mixed to make a thick batter, then allowed to ferment overnight. The same lactic acid bacteria found in fermented milks and creams (Leuconostoc mesenteroides, Lactobacillus delbrueckii and and L. lactis, Streptococcus faecalis L. lactis, Streptococcus faecalis) as well as some yeasts (Geotrichum candidum, Torulopsis species) feed on the sugars and produce acids, aroma compounds, carbon dioxide gas, and viscous, sticky carbohydrates that thicken the batter and help trap the gas bubbles. The batter is then steamed to produce a spongy, delicately flavored cake. species) feed on the sugars and produce acids, aroma compounds, carbon dioxide gas, and viscous, sticky carbohydrates that thicken the batter and help trap the gas bubbles. The batter is then steamed to produce a spongy, delicately flavored cake. Dhokla Dhokla is a similar preparation made using rice and chickpeas. The is a similar preparation made using rice and chickpeas. The dosa, dosa, a large fried disc, crepe-like but crisp, is made from a thin fermented batter of rice and black gram. a large fried disc, crepe-like but crisp, is made from a thin fermented batter of rice and black gram. Papadums, Papadums, a familiar side dish in Indian restaurants in the West, are thin wafers of black gram paste that has been allowed to ferment for a few hours before being cut into discs and dried; they're then fried and develop a blistered, delicately brittle texture. a familiar side dish in Indian restaurants in the West, are thin wafers of black gram paste that has been allowed to ferment for a few hours before being cut into discs and dried; they're then fried and develop a blistered, delicately brittle texture.

Soaking Times Depend on Temperature Medium-sized beans absorb more than half of their total water capacity in the first two hours of soaking, and plateau at about double their original weight after 1012 hours. As the soaking temperature goes up, absorption accelerates; and if the beans are first blanched for 1.5 minutes in boiling water, the subsequent water absorption takes only two to three hours in cool water, because the blanching rapidly hydrates the seed coat that controls water movement. Medium-sized beans absorb more than half of their total water capacity in the first two hours of soaking, and plateau at about double their original weight after 1012 hours. As the soaking temperature goes up, absorption accelerates; and if the beans are first blanched for 1.5 minutes in boiling water, the subsequent water absorption takes only two to three hours in cool water, because the blanching rapidly hydrates the seed coat that controls water movement.

Salt and Baking Soda Speed Cooking Cooking times can be reduced even more by adding various salts to the soaking water. Plain salt at a concentration around 1% (10 g/l, or 2 teaspoons/qt) speeds cooking greatly, apparently because the sodium displaces magnesium from the cell-wall pectins and so makes them more easily dissolved. Baking soda at 0.5% (1 teaspoon/qt) can reduce the cooking time by nearly 75%; it contains sodium and in addition is alkaline, which facilitates the dissolving of the cell-wall hemicelluloses. Of course, added salts affect both the taste and texture of the cooked beans. The alkalinity of baking soda can give an unpleasantly slippery mouth feel and soapy taste. And salt reduces the swelling and gelation of starch granules within beans, which means that it favors a mealy internal texture over a creamy one. Cooking times can be reduced even more by adding various salts to the soaking water. Plain salt at a concentration around 1% (10 g/l, or 2 teaspoons/qt) speeds cooking greatly, apparently because the sodium displaces magnesium from the cell-wall pectins and so makes them more easily dissolved. Baking soda at 0.5% (1 teaspoon/qt) can reduce the cooking time by nearly 75%; it contains sodium and in addition is alkaline, which facilitates the dissolving of the cell-wall hemicelluloses. Of course, added salts affect both the taste and texture of the cooked beans. The alkalinity of baking soda can give an unpleasantly slippery mouth feel and soapy taste. And salt reduces the swelling and gelation of starch granules within beans, which means that it favors a mealy internal texture over a creamy one.

Pressure Cooking Thanks to its temperature of around 250F/120C, pressure cooking can cut the cooking time of beans and peas by half or more. Salt-presoaked beans may take just 10 minutes. Thanks to its temperature of around 250F/120C, pressure cooking can cut the cooking time of beans and peas by half or more. Salt-presoaked beans may take just 10 minutes.

Persistently Hard Beans One problem that cooks commonly encounter when cooking dry beans is that some batches take unusually long to soften, or never quite do soften. This may have been caused by growing conditions on the farm, or storage conditions after harvest. One problem that cooks commonly encounter when cooking dry beans is that some batches take unusually long to soften, or never quite do soften. This may have been caused by growing conditions on the farm, or storage conditions after harvest.

"Hard-seed" is a characteristic found in beans when temperatures are high and humidity and water supply are low during the growing season. The outer seed coat gets very water-resistant, so it takes much longer for water to move into the bean interior. Hard-seed beans are usually smaller than normal beans, so they can sometimes be avoided by picking over the beans and discarding the smallest ones before cooking.

"Hard-to-cook" beans, on the other hand, are normal when harvested, but become resistant to softening when they're stored for a long time - months - at warm temperatures and high humidities. This resistance results from a number of changes in bean cell walls and interiors, including the formation of woody lignin, the conversion of phenolic compounds into tannins that cross-link proteins, and the denaturation of storage proteins to form a water-resistant coating around the starch granules. There's no way to reverse these changes and make hard-to-cook beans as soft as regular beans. And there's no way to spot them before cooking. Once cooked, they're likely to be smaller than normal and so may be picked out before serving.

The Composition of Dry and Sprouted Legumes

Legume Seed Water Water Protein Protein Carbohydrate Carbohydrate Oil Oil

Common bean 14 14.

22 22.

61 61.

2 2.

Fava bean 14 14.

25 25.

58 58.

1 1.

Lima bean 14 14.

20 20.

64 64.

2 2.

Mung bean 14 14.

24 24.

60 60.

1 1.

sprout 90 90.

4 4.

7 7.

0.2 0.2.

Soybean 10 10.

37 37.

34 34.

18 18.

sprout 86 86.

6 6.

6 6.

1 1.

Lentil 14 14.

25 25.

60 60.

1 1.

Chickpea 14 14.

21 21.

61 61.

5 5.

Pea 14 14.

24 24.

60 60.

1 1.