The Truth About Cooking Beans

October 16, 2008

I cooked dried beans for the first time a few nights ago (for burritos), so I wanted to find out what you really need to do to cook beans. Some people claim you have to soak them overnight, others say don’t bother, while some say soaking just reduces the flatulence effect. To get to the heart of the matter I went straight to McGee.

A dry bean has four main parts. First, the embryo is the plant part that is supposed to grow. The embryo is sandwich between the cotyledon, which is the majority of the bean and consists of starch and proteins. If the bean were to grow, the embryo would feed on the cotyledon. The cotyledon is surrounded by the seed coat, which is mostly made up of cell wall compounds, including hemicelluloses (you may remember hemicelluloses from such posts as Why Cell Walls Are Important to Your Cooking). The final part of the bean is called the hilum – this is where the stem originally attached to the bean and the only point at which a dry bean can absorb water.

Soaking Beans

The seed coat prevents the bean from absorbing water initially, and water can enter only through the hilum, but after 30-60 minutes of soaking in cold water, the seed coat is permeable to water, allowing water to enter the bean from any part of the surface. Even after becoming permeable, however, the seed coat limits water absorption. Additionally, the seed coat becomes permeable more quickly in hot water.

Pre-soaking your beans can reduce cooking time by up to 25% because much of the cooking time is often just water penetrating into the bean. In cool water, a bean can absorb about half its total water capacity in two hours, and double its weight in 10-12. If you blanch the beans for a minute and a half in boiling water before soaking, however, the full soaking time in cool water is reduced to two or three hours. This occurs because the hot water makes the seed coat permeable, as mentioned above.

Slowing Cooking and Stabilizing the Bean

Acids, sugar, and calcium all have the same effect on bean cooking – they reinforce the seed coat, slowing cooking and helping beans maintain their shape. Acids stabilize the hemicelluloses in the seed, preventing them from dissolving as quickly, sugars reinforce the cell wall structure, and calcium reinforces the cell wall pectins.

Additionally, when salt is added to cooking beans, it will slow the rate of water absorption, prolonging how long it takes to cook the beans. Magnesium from hard water has the same effect of the compounds above – it reinforces the seed coat.

Speeding Up Bean Cooking

While salt added to cooking beans will lengthen their cooking time, salt added to the soaking water of beans will shorten the subsequent cooking time. Supposedly the sodium in salt replaces magnesium in the pectins of the cell walls, leaving them open to dissolving. McGee does mention, however, that beans soaked in salted water will have a more mealy texture because salt stops the swelling of starch molecules.

Alkaline compounds have the opposite effect of acidic compounds – they dissolve hemicelluloses, reducing the cooking time of beans greatly.

Baking soda at .5% (1 teaspoon/qt) can reduce the cooking time by nearly 75%…[but] can give an unpleasant slippery mouth feel and soapy taste. (McGee, On Food and Cooking)

These methods are clearly not without their drawbacks. Pressure cooking can speed up cooking times however, without the side effects. I don’t have a pressure cooker, but it can cut cooking times in half without creating a soapy taste.

Posted in Food Science |