Purchase whole untreated mung bean seeds. If they are not available in the grains section of a local grocery store or health food store, you can find them online.
Thoroughly clean and rinse a quart size glass canning jar. Place 3 to 4 tbsp. of whole raw mung beans into the jar. Fill the jar with fresh water to cover the seeds. Set aside for several hours.
Place a few layers of cheesecloth over the top of the jar. Place the outer lid ring on the jar to hold the cheesecloth in place. The holes in the cheesecloth layers should be small enough that the seeds can not pass through.
Drain off the water after the seeds have soaked for a few hours. Keep the cheesecloth in place to prevent the seeds from washing out of the jar. Gently shake the mung bean seeds evenly across the inside of the jar so they are evenly spaced.
Lay the jar on its side inside a dark cupboard. The darker the area the longer the sprout roots will grow seeking light. Small cotyledons on sprouts are greener when exposed to light and the flavor will change. Too much light will cause the sprout to produce true green leaves on short roots.
Gently wash the new sprouts with clean water and drain immediately two or three times a day. This keeps the young sprout growing. Drain off excess water to prevent rotting.
Mung bean sprouts are ready to use when 2 to 3 inches long, white, juicy and crisp. Rinse and drain before eating.