When it comes to green beans, we all owe a great debt to Julia Child, who was adamant that they must be cooked until tender, not simply blanched, as has been the custom among certain trendy chefs for the last couple of decades. There seemed to be no easier way to incur Child's wrath than to serve her undercooked green beans. Most of the home cooks I know have taken this to heart or else simply know it intuitively — all you need to do, really, is taste — but too many restaurants are still serving raw or nearly raw green beans.
Why is this so important? It's not simply about about texture. A green bean's flavor does not blossom fully until it is cooked. And exactly how long is crucial, too, as flavor fades quickly if a green bean is cooked too long.
Exactly how much time a green bean needs to be cooked varies by variety and, to some degree, size. The tiny haricot verts that Nancy Skall of Middleton Farms grows require only about 90 seconds, while full-sized Blue Lake green beans can take 7 to 10 minutes.
Yet size is not a reliable measure when it comes to Romano and other flat green beans. The luscious Spanish Musica, another specialty of Middleton Farms, requires just 3 to 4 minutes; cooked longer, the flavor drops off. Yet other flat green beans can take twice as long.
Unless you know a variety of bean well, you need to test for doneness every 30 seconds or so. What you are looking for is a bean that you can bite through easily but that still retains texture. If you have to struggle to bite through it, it's not done; if it falls apart in your mouth, it is overcooked.
For the best flavor, do not skimp on salt. You want at least a tablespoon of salt for every two quarts of water.
It is important, as well, to use a large pot and a lot of water so that it will return to a boil as quickly as possible after you add the beans. In “Julia and Jacques: Cooking at Home” (Knopf, 1999, $40), Child suggests plunging a solid metal poker, heated over a burner, into the water when the beans are added. This helps the water return to a boil quickly, which in turn sets the color of the bean.