Pinto beans are known to be difficult to sprout. The pinto bean is grown most widely for long-cooked soups and other dishes. Because of that, it is simply not as prone to sprouting as other varieties of pinto beans.
Like other beans, you only want to sprout the bean a little bit. One quarter inch of sprout is enough to get the job done. Because of their lower germination rate, you can consider your sprouts done even if only 50% of them have sprouted.
The Pinto Bean Sprouting Process:
First you need to decide how far you want to take the sprouting process. For all cooking purposes, use a shorter-sprouted pinto bean. For raw eating in salads or sandwiches a longer sprout may be desirable.
The longer sprout will take up a lot more room. Plan to use a larger vessel such as a colander or a gallon jar for two cups of long-sprouted pinto beans. For the short-sprouted pinto beans a quart or half-gallon jar is sufficient.
Rinse and soak the pinto beans overnight.
In the morning drain and rinse the pinto beans thoroughly. When using a jar with a sprouting screen, invert that jar to allow any extra water to run off. Leave a colander over a bowl or sink and cover it with a towel in order to keep air flowing while keeping bugs out.
After about 6 hours, rinse the pinto beans again. Two to three times per day is optimal, always rinsing more frequently in warmer weather.
Repeat the rinsing and draining process until the pinto beans have sprouted to the desired length. For short-sprouted pinto beans (ideal for soups, stews, etc.) this should take around 3 days. For longer sprouted pinto beans this could take up to 6 days.
Once the pinto beans are sprouted, give them a final rinse and thorough draining. It is normal that the skins come off many of the beans. Either pick the skins out or leave them in; they do not affect the flavor or digestion.