Hulling mills
Hulling mills, also known as huller mills or dehuller mills, are industrial machines used primarily in the agricultural and food processing industries. Their main purpose is to remove the outer husk or hull from various types of seeds, grains, or fruits. This hull removal process is important because the hulls can be tough, indigestible, or unpalatable, and removing them improves the quality and usability of the underlying product.
Hulling mills are the machines used to remove the hull or outer covering from seeds and grains such as rice, oats, barley and coffee beans. The hull, or husk, is the outermost layer that has to be taken off before the seed or grain can be processed further, which makes hulling one of the first unit operations in a grain or seed processing line. Hulling mills are commonly used in the food industry and are an essential part of the processing of many crops.
The process works by passing the seeds or grains through a machine that uses a combination of friction, impact and compression to remove the hull. In operation, the food product is fed into the mill through a hopper. Inside, it comes into contact with abrasive surfaces that rub against the outer layer; the friction generates heat and causes the hull to loosen. Pressure is then applied to separate the hull from the edible portion, by methods including rolling or crushing. Finally, the separated hulls are removed using a separator or sieves, leaving behind the inner, edible portion.
Products commonly processed using hulling mills include rice, where the outer husk of the grain is removed; coffee, where the parchment layer and outer skin are taken off; oats, where the inedible outer husk is removed before further processing; buckwheat, whose outer shell is known as the hull; sunflower seeds, hulled to produce the inner kernel; spelt, hulled before use in baking or other food products; and millet, where the outer layer is removed before cooking or use in other food products.