Rice Milling
Applied Milling Systems has decades of experience in the rice milling industry. Our people have been involved in the design, commissioning and optimization of several of the largest and most modern rice milling facilities in North, Central, and South America.
We have designed and supplied some of the most modern rice flour milling facilities in operation that can produce 1,000,000 pounds per day of rice flour. Rice flour volumes continue to rise, partly due to increased demand for gluten-free products. Rice flour may also be used for extruded products and even producing reformulated rice from rice brokens, all of which we can produce through partnering technologies.
Long, medium, or short grain; parboiling or white rice; from receiving to packaging and everything in between, AMS has the experience to provide you with a state-of-the-art rice processing facility.
Intake / Precleaning
Rough paddy rice arrives in 50kg bags and in bulk (truck and railcar). We have systems to efficiently intake the paddy rice. The rough rice contains impurities and one objective of this operation is to pre-clean the grain to remove large impurities and ferrous materials which may damage or choke downstream equipment.
Drying
In the case that rough paddy rice arrives as ‘green’ rice directly from the fields, the grain proceeds from intake / precleaning to what is called wilting bins. After a particular amount of time in the wilting bins, the green rice is conveyed to the drying section. In this section, the grain is carefully dried to avoid fissures and discoloration in multiple passes, generally in tower (column) dryers or a combination of fluid bed dryers and tower dryers. AMS offers both of these drying solutions.
Cleaning
This section further cleans the rough rice to remove finer impurities such as smaller chaff, loose husk, seeds, dirt/sand, ferrous materials, and other impurities. After cleaning, the grain is then referred to as simply paddy rice and is ready for subsequent processing.
Husking / Dehulling
Paddy rice contains a very abrasive outer coating which is called the husk, or hull. Before the grain can be considered brown rice and ready for further processing, this husk / hull must be removed. This is done by machines that are commonly called huskers, shellers, or dehullers. These machines generally contain a pair of rubber rolls operating at different speeds. The paddy rice is directed in between the pair of rolls which ‘splits’ the husk / hull from the inner piece of grain (brown rice). The grain and husk is then passed through an aspirator to aspirate the loose pieces of hull from the brown rice stream.
Paddy Separation
In one pass, the huskers are typically not 100% efficient. This is done purposely as to not have to apply too much pressure on the husking rolls and break the rice. This means that the brown rice stream still contains paddy rice which still has the husk intact on the grain. The brown rice and the paddy rice have different densities. The purpose of the paddy separation section is to use a density separation to separate the paddy from the brown rice stream and return it to the husking section where the husk can then be removed.
Milling
The brown rice can then be cleaned further at that stage and be sold as brown rice. Or, the rice can proceed to the milling section of the plant to produce milled rice, or polished white rice, and a separate bran stream. The milling of the brown rice can be done in a single pass or multiple passes, the latter which is typically more gentle and will produce higher yields of whole milled rice. The milling section is generally comprised of a combination of abrasive and friction machines. Abrasive machines remove the outer layers of the grain by an emory, or gritty, suface. The abrasive machines are followed by friction machines which do not use abrasives, but rely on more grain-to-grain friction to remove the inner layers of bran. The last step in the milling step is to pass the milled rice through a mist polisher to give the rice a shiny, polished appearance.
Grading
After milling, the polished rice is a combination of whole rice (commonly called head rice), and broken rice (commonly called second heads), and smaller pieces generally called brewers. The purpose of the grading section is to separate the polished rice into these three streams as they have different monetary values and are sold separately. Grading is done using a combination of sifting techniques and cylinder separators which can determine the difference in length between the head rice, second heads, and brewers.
Optical Sorting
The polished head rice and second heads streams, and sometimes the brewers stream, are then passed through optical sorting machines (aka color sorters). These machines are a last pass before the product is deemed finished product. These machines are able to detect grains that have dark specks, or other discolorations, and can reject them with a pulse of air from the main product stream. These machines are also often able to detect and reject other impurities such as stones, adobe, glass, and more.
Loadout / Packaging
After the optical sorting section, the grain is transferred to storage, generally via a series of magnets and metal detectors. The product is then ready to be packaged in various size packages or bags, or to be shipped out via a hopper truck or railcar.