Poke 8 to 10 holes in the lid of a jar capable of holding at least 1 quart.
Pour out 1/3 cup of mung beans for every quart of bean sprouts desired. Make sure the germinating bean sprouts won't outgrow the size of the jar being used. Pick out any discolored or odd-looking beans and discard them.
Dump the beans into the jar. Cover the mung beans with cold water.
Screw the lid onto the jar and set the container in a cool, dark place. Inside a cupboard works nicely. Leave the jar sitting in the cupboard overnight.
Dump out the water the next morning by holding the jar upside down over a sink. Look for signs of germination in the beans -- it may have already started.
Lay the jar horizontally in the dark cupboard. The mung beans should rest on the side wall of the jar.
Rinse the beans with cold water every morning. Drain the jar immediately afterward. Watch for the mung beans to germinate and begin to grow into bean sprouts. Germination occurs quickly, forming usable bean sprouts within four days.