You can add salt to your beans at any time, says Lynne Bigwood of the Northarvest Bean Growers Association. “According to research, dry beans cook faster when salt is added because salt helps break down the cell walls,” she says. But don’t expect a miraculously quick-cooking pot of beans, warns Dr. Barry Swanson, professor of food science at Washington State University: Salt only affects the rate of softening by a matter of minutes when used at the concentrations we find palatable.
There have been multiple studies confirming that salt speeds up the cooking time of beans. A 1977 study published in the Journal of Food Science found that beans would soften more rapidly when they were soaked in salted water. In 1982, those results were confirmed by another study published in the Journal of Agriculture and Food Chemistry. In March 2008, the Cook’s Illustrated test kitchen found that soaking beans in salted water (three tablespoons per gallon) produces softer skins in your cooked beans. It also makes your beans taste better, as the salt penetrates the whole bean, rather than only flavoring the surface.
So what about beans that take forever to cook or never soften at all? They’re too old. Water enters most beans not through their outside coats, but through three tiny openings on the side of the bean called the raphe, hilum, and micropyle. “As the bean ages, those pores tend to close up and leave no access for water,” explains Dr. Swanson.
You can’t really tell a bean’s age from looking at it, so the best way to avoid old ones is to make sure you’re buying them from a store with good turnover, says Bigwood. Also, place them in an airtight container and store it in a cool spot to keep the beans from drying out as quickly.
Here’s what Chowhounds have to say about salting dried beans.