Food products come from agriculture and often arrive at the processing plant contaminated with stones and other debris. A destoner is a machine that is designed to remove this. It operates on the principle that field trash — not only stones but also glass and pieces of metal — tends to be heavier than the product, which is often a grain or seed, etc. A regular sifter would not be effective because the impurities are often roughly the same size as the product. The destoner often operates with a vertical air stream that lifts the product and blows it into an upper portion of the machine while the heavier trash falls to the bottom.
The wide variety of product that must be destoned, varying from small, light products, such as grains of wheat, to larger, hearvier products, such as nuts, means that there are different types of destoners. However, most destoners operate with air blowers and a vibratory deck of some sort. The destoner must be rugged enough to survive under years of vibration and abrasion. They must also be easy to clean out. They must be effective in removing all the stones so that they do not damage downstream processing equipment, such as hammer mills. In most cases, corrosion is not a major problem so they are not usually constructed out of stainless steel.
Some of the leading manufacturers of destoners are Buhler, Forsbergs and Lewis M Carter (LMC) which includes Carter Day Intl. Buhler is a Swiss company that is known for feed grain equipment. Forsbergs is also known for feed grain equipment and is based in Minnesota. Lewis M Carter began as a peanut processing company in Georgia but its Carter Day division is based in the grain growing region of western Canada.