Tannins are a group of chemical compounds found in plants, fruits, vegetables, nuts, wine, and tea. They are also known as tannic acid. Properties Tannins are large, water-soluble molecules that bind to proteins, cellulose, starches, and minerals They are bitter and astringent Tannins have antioxidant properties Uses Tannins are used in medicines, fabrics, leather, and ink Tannins are used in the production of leather by changing the structure of animal hide.