Make sure you start with untreated broccoli seeds. Put one tablespoon of seeds into a clean canning or other large jar. Cover the top with a piece of cheesecloth secured with a rubberband. Rinse the seeds twice a day with warm water, draining completely each time. Spouts are ready to eat when they are one or two inches long and have tiny green leaves.
Broccoli sprouts have tiny root hairs that look like mold.
As long as you're rinsing and draining twice a day, you shouldn't have any problem.