Blanched beans are beans that have been briefly submerged in boiling water. There are a number of reasons why cooks choose to blanch beans, but the most common are to briefly cook the beans, softening their texture and enhancing their flavor; to prepare beans for freezer storage; and to stop enzyme production and thus stymie the growth of bacteria. Almost any kind of bean can be blanched successfully, though green beans and snap beans are among the most popular candidates.
The blanching process itself is relatively simple. A cook must bring a pot of water to a boil, usually at a ratio of one gallon (about 4 liters) of water for every pound (0.5 kg) of beans. Once the water has reached a rolling boil, the cook adds the beans and watches them closely for a short amount of time. Blanched beans must boil for anywhere from 30 seconds to three minutes, depending on their type, tenderness, and intended purpose. When the time is up, the cook removes the beans from the pot and plunges them into an ice water bath to bring them back to resting temperature.
Beans will rarely cook through in the short amount of time they have in the water. As such, blanching beans is never an effective way of cooking beans. It does have certain benefits where taste, texture, and preservation are concerned, however.
Blanching is a common way of preparing beans that have been freshly picked. Raw beans are normally fine to eat, but briefly boiling them is a good way of enhancing their flavor and texture both. Blanched beans’ brief exposure to very hot water heightens their color and brings nutrients more readily to the surface. This usually also contributes to a more crispy exterior.
Most of the time, people who grow beans have harvests that far exceed what can be eaten in a given season. Sometimes beans are pickled or canned to save, but they are also frequently frozen. Food safety experts almost always recommend blanching all vegetables and beans before freezing them. Blanched beans often last longer in the freezer because the blanching process helps prolong their freshness. They are also much more sterile.
Bacterial growth is a serious concern for produce stored in the freezer. Although a bean may be frozen, its enzymes are usually still active, and can trigger bacterial growth as the beans defrost. This rarely happens with blanched beans, however, in large part because the boiling water locks the bean's growth, killing and preventing germs. Blanched foods are still considered raw. They are simply safer on account of the brief boiling.