Microcrystalline cellulose (MCC) is non-digestible plant matter in sources like wood pulp and tough plant stalks. These plants are harvested, cleaned and ground to create a fine, white powder. It is called “microcrystalline” because its tiny crystals can only be viewed under a microscope. Microcrystalline cellulose is a common addition to products not for nutritional value, but for various other purposes.