Always do what your mother says. When I was a kid my mother told me that if I wore my rubber rain boots in the movies it would ruin my eyes. I forgot to take them off once, and today I have to wear glasses.
But seriously, your mother’s dictum is somewhat more rational.
Garbanzos, the Spanish name for what Italians call ceci and we call chickpeas, are often sold in dried form, hard, tough-skinned beans that are notoriously difficult to soften. In many South Asian, Middle Eastern, and Mediterranean countries, one of which your grandmother may have come from, it has long been the custom to soak dried garbanzos at least overnight before cooking them. It was also found that a bit of baking soda shortened the soaking and cooking time.
We now know that alkalis such as bicarbonate of soda attack the fibrous cellulose skins and make them more permeable to water. Various alkalis (lye, potassium carbonate, lime) are used in other cultures to remove the cellulosic hulls from corn kernels in order to make such foods as hominy and masa harina, the dough used to make tortillas. We also know that a pinch of baking soda is particularly helpful if the beans are being soaked or cooked in hard water, because bicarbonate removes the calcium and magnesium in the water, which otherwise could form hard, insoluble compounds in and between the beans’ cell walls and make the beans less susceptible to hydration. Too much baking soda, however, will soften the beans too much and spoil their texture, not to mention contributing a soapy, salty flavor.
But is it really necessary to soak dried garbanzos or other dried legumes in water before cooking them? Drying, which obviously predates canning by many centuries, is simply a way of preserving beans and other legumes for storage. It is still used for convenience in packaging and ensures a long shelf life. These days, however, you can buy many types of beans in cans, already cooked and soft.
Almost as much has been written, and argued, about soaking dried beans as about the 2000 presidential election, and in my opinion just as futilely. To soak or not to soak just doesn’t have a simple answer.
The original reason for soaking was undoubtedly that it reduced the cooking time and therefore conserved valuable fuel. Today, most of us don’t have to chop wood for cooking, and the small amount of gas or electricity saved by soaking matters little in our prodigal society. Inasmuch as soaking dried legumes has the same major objective as cooking them, making them soft and chewable, it’s mostly a matter of how you want to split that chore between a preliminary soak and a hot-water simmer. The three relevant factors are size, temperature, and time.
• Size: Tiny lentils and small peas, especially split peas, have large surface areas compared with their weights or volumes (that is, they have a high surface-to-volume ratio), so water is offered abundant entryways into their interior. Since they hydrate quickly during cooking, there is little reason to give them a cold-water head start.
Relatively bowling-ball-sized garbanzos, on the other hand, have a smaller surface-to-volume ratio, and the water has farther to go to penetrate into their centers. For these virtually impregnable seeds, a preliminary soak in cold water may well cut the cooking time down to a finite number of hours.
• Temperature: The diffusion of water into dried seeds occurs more rapidly at an elevated temperature. Thus, an hour of simmering at the boiling point is much more productive than an hour of soaking in cold water. By comparing likely diffusion rates, I estimate that an hour of simmering accomplishes as much hydration as 3 hours of cold soaking. So if it would take 5 hours of simmering to bring dried garbanzos to a toothsome texture, you could do it in only 4 hours of simmering if you first soaked them for 3 hours.
• Time: How much time you have available is a consideration, as is what kind of time, attended (simmering) or unattended (soaking). It’s tempting to do a lot of soaking because you can do it while you sleep, but trading off too much simmering for soaking can adversely affect the flavor of the finished dish. You want enough cooking time to allow the softened beans to absorb and release flavors from and to whatever other ingredients are keeping them company in the pot.
Oceans of ink and tons of hot air have been spilled over such questions as whether soaking affects the ultimate texture of the beans; whether to salt the beans (if at all) before or after simmering; whether soaking beans removes nutrients and flavors or removes gas-forming oligosaccharides. In the former case you would want to discard the soaking water, while in the latter case you would want to retain it. Research appears to show that small amounts of both oligosaccharides and thiamine (vitamin B1 ) are extracted into the soaking water, reducing both nutrition and emission. You can’t win.
But cooking beans is neither rocket surgery nor brain science (or something like that). Over the centuries, many different traditional means of dealing with beans have evolved in different cultures, without much scientific justification. So just do ’em the way your own ethnic background decrees.
And if it makes you feel righteous to “honor thy mother,” by all means go ahead and soak ’em just because she told you to.