SOY SPROUTS Any variety can be used to make bean sprouts, but usually smaller varieties, such as the mung bean, are preferred. Sprouting to maturity needs from five to ten days after watering has begun. During sprouting most of the undesirable carbohydrates are metabolised, the protein digestibility improves and the trypsin inhibitors are inactivated. Unique is the formation of ascorbic acid (vitamin C) during sprouting.