Cryogenic grinding is a method of powdering herbs at sub-zero temperatures ranging from 0 to minus 70°F. The herbs are frozen with liquid nitrogen as they are being ground. This process does not damage or alter the chemical composition of the plant in any way. Normal grinding processes which do not use a cooling system can reach up to 200°F. These high temperatures can reduce volatile components and heat-sensitive constituents in herbs. The cryogenic grinding process starts with air-dried herbs, rather than freeze-dried herbs. Solid materials are ground or pulverized by way of hammer mills, attrition mills, granulators or other equipment. A smaller particle size is usually needed to enhance the further processing of the solid, as in mixing with other materials. A finer particle also helps in melting of rubber and plastics for molding. However, many materials are either very soft or very tough at room temperatures. By cooling to cryogenic temperatures with liquid nitrogen, these may be embrittled and easily fractured into small particles. Cryogenic grinding was shown to significantly affect active constituent levels in herbs. Test results showed an average increase of 15.6% in constituents tested in four medicinal herbs when they were ground cryogenically. The range was 10.7% to 21.8%, indicating that some herbs are affected more than others by the temperatures at which they're ground.