Spinach can hold a lot of dirt and must be thoroughly washed before using. To clean, fill a large bowl with water, then swish spinach around in water until most of the dirt comes off. Repeat process 2 or 3 times, using clean water each time, until no more dirt clings to the spinach. Rinse thoroughly under running water and remove hard stems. Spin dry in salad spinner and/or pat dry with paper towels. Use immediately or store in refrigerator up to 4 days.