Native to South Asia from Pakistan through Bangladesh, these small squarish beans are now widely grown in East Asia and around the world. The dark green beans are most familiar to Americans as the source for the common bean sprout, but they are much more important as dried beans and dal in India. Mung beans are also the bean used to make transparent bean thread noodles popular in East Asian cooking as well as bean jelly and many desert dishes.
Pictured are the whole beans and the split and peeled form (dal). Indian markets also often have this bean in split but unpeeled form, and sometimes in whole peeled form. The dal is easily recognized because it's more yellow than the dal of similar beans. The photo specimen whole beans were typically 0.25 inch long and 0.15 inch wide (6.4 x 3.8 mm). The Dal was 0.20 inch long and 0.12 inch wide (5.1 x 3.0 mm).
More on Varieties of Beans.
Buying: Whole mung beans are easily available in South, East and Southeast Asian markets, and the dal is available in any market serving an Indian community.
Storing: Keep beans or dal cool and dry in a sealed container and mark the container by date purchased. Technically they'll last for years without spoiling - BUT in practice a year is maximum. With age they cook less and less well until they simply will not soften, no matter how long you soak them and how long you cook them.
Soaking: Whole mung beans need to be soaked in lightly salted water at least 4 hours and preferably 5. You'll need 2-1/4 cups of soaking water for every cup of beans. The dal needs to be soaked for at least a half hour, but if it's old even a couple hours won't help much.
Cooking: Whole soaked beans will cook in about 45 minutes. Unsoaked they'll need at least an hour, maybe more, and they tend to fall apart a lot more than soaked beans. Soaked dal should be cooked for around 1/2 hour depending on how soft you want it. In India it's normally cooked until like a thick soup, but if the dal is old it will never soften.
Mung Bean Sprouts
Buying and Storing: Any market serving an East or Southeast Asian community, most produce stores and many supermarkets will have these. Look for very crisp white stems with no sign of discoloration. The root end will always be discolored as in the photo, and they will often have some of the green shells adhering to the leaf end, but those should rinse away.
Prep: In general, you just rinse them. In Korea, no respectable housewife would think of serving bean sprouts without neatly pinching off the ugly root end, but we're not usually that picky in North America. Sometimes packages with the root end cut off can be found in Korean markets, but more often that's done with the larger soybean sprouts.
Cooking: Less is best. In North America we often serve
them raw, but in China, where nothing is served raw (due to traditional
agricultural practices), they are generally cooked just until no longer
brittle. In some cases they are squeezed dry after a brief cooking.
Bean Thread Noodles
Raw, these noodles look almost exactly the same as Rice Sticks, but they must not be confused. Cooked they are totally different and not at all interchangeable.
Buying & Storing: These can be found in any market serving an East or Southeast Asian community - and in most supermarkets. In a cool, very dry place they will keep for two or three years without degrading significantly.
Cooking: These noodles are always soaked in warm water
for about 20 minutes (soaking longer isn't going to further soften them).
They are then added to recipes at the very last moment and given the
minimum cooking that will bring them up to temperature.
Mung Bean Jelly
This product is sold as 1 pound blocks with the consistency of stiff Jello. The block this cross section was cut from was 4-1/2 inches wide and 1-3/4 inches thick. Mung Bean Jelly is most popular in Korea, but a version is used to a lesser extant in southern China.
Buying: This product is most available in Korean markets.
It will usually be stocked refrigerated with similar blocks of other gels.