Production

II. Rice Production in the World and in the U.S. (continued)

	TERMS AND CONVERSIONS
World Production of Rice U.S. Production of Rice Farming of Rice Storage and Milling of Rice The U.S. Rice Milling Industry	Most production figures related to paddy or rough rice. (Rice that still contains the husk). Most demand figures relate to milled rice. Milled rice is about 68% of paddy.	Most U.S. figures use cwts (hundred weights, 100 lbs). Large numbers are reported as 1000 cwts. World figures use Metric Tons. 1 MT = 2204 lbs or 22.046 cwts. Large numbers are one million MT.
	NOTE: Check in another section of Rice 101 for definitions of grain types, parboiled rice, broken rice, paddy rice, etc.

Storage and Milling of Rice. See Photos associated with the Milling Process Rice from the field is harvested and threshed to produce what is most often called paddy rice or rough rice. Rice is usually harvested at about 18% to 24% moisture and must be dried down to about 12% to 14% so that it can be safely stored. In most developing countries rice is somehow air-dried. The straw and rice can be dried in the field. It is sometimes stacked in a special manner to allow air to pass to through it and cause rain run off quickly. Most often, the paddy rice is spread on some sort of concrete or pavement and raked over until dry. In some developing countries, you will see rice drying all over the roads during harvest season. In more developed countries, rice is dried in farm storage bins that have air chambers underneath that force air to pass up through the rice, or rice is dried in large column dryers where the rice makes two to five passes through the dryer in a continuous flow type system. Drying of the rice (including while in the field prior to harvest) is a critical component in regards to quality. Rice that is cracked during drying will have a lower percentage of head yield and will have a poorer quality after cooking. Milling of the rice involves; removing the trash and then the husk from the rice, milling the bran off of the endosperm (leaving white rice), and then removing broken kernels and other defects. There are many ways that rice can be stored and milled. In much of the world, the rice is milled in very small mills near the farm and stored in the form of milled rice until consumed. Sometimes it is stored as paddy or brown rice and then milled fresh prior to consumption. Thailand, Japan, and the U.S. are good examples of how different the systems can be. In Thailand, most rice is milled to white in small mills near the point of harvest and very soon after harvest. The rice is then stored in 50 or 100 KG jute bags in a small storage shack or in a farmers home. At some point, the rice will be sold to a large rice milling and trading company in Bangkok. The milled rice in jute bags will accumulate in a large warehouse in Bangkok where it will usually be remilled and blended for the export market. Back to TOP In Japan, the rice will be husked and made into brown rice near the field soon after harvest. These brown mills can be very small or can be as large as 100 ton per day (brown mills are usually operated by a cooperative). The brown rice is packed in woven poly bags and stored in cool temperature and humidity controlled warehouses until ready for milling. Japanese rice mills tend to be the most sophisticated in the world, but are rarely more than 100 MT per day. (This is relatively small when compared to U.S. mills that can handle 1000 MT per day.) The Japanese are extremely particular about rice quality. They go to great lengths to prevent cracking of the rice (humidity controlled warehouses to maintain moisture at 14% to 15%) and they believe that rice is best when served fresh after milling. There are many stores in Japan, where small machines mill brown rice as it is purchased. (Of course this obsession with quality has a price and Japanese rice is about 5 times the price of rice in other countries.) In the United States, most of the rice is dried and then stored in large commercial dryers. The rice is stored in the form of paddy rice. It remains in bulk in the paddy form until time for milling. The paddy rice will be shipped via truck, rail, or barge in bulk to a large mill where it will be milled and packed for either the domestic or export market. This is a very efficient system. Freight is cheap in the U.S. and so transportation of paddy rice (which involves the unnecessary hauling of husks and bran) to a large central milling location makes sense. Most smaller mills in the U.S. handle at least 200 MT per day (milled basis) and the largest mills can mill up to 1000 MT per day. In the U.S. the milling operation is year round and not just at harvest. Back to TOP


	In the U.S., Japan, Australia, Europe, and now some of the developing world, the milling of rice has become a very sophisticated process. Following is a description of the basic components of the process.
			Grain Cleaning. The paddy rice is passed through coarse screens to remove all straw, stones, and other objects that are larger than the rice. The rice passes over fine screens to remove small weed seed, sand and dirt, stones, and other objects smaller than the rice. Air separation systems are sometimes used in this process.

			Destoning. The rice is passed through a specific gravity table that separates the product by density. Stones are separated from the rice.

			Husking. The husk is removed from the rice. This is most often done by passing the rice through two spinning rubber roles. One roll is spinning faster than the other. The rubber rolls are tightly pressing against the rice from both sides and strip the husk off.

			Paddy Separation. A portion of the rice leaving the husking operation still has the husk on the kernel. A paddy separation machine that works with specific gravity separates the light paddy kernels from the heavy brown (husks removed) kernels. The paddy kernels go back to the huskers.

			Milling. There are many machines and methods designed to remove bran from the rice. The Japanese milling system is most often used in the most modern mills. With this system, the rice is first passes through a milling chamber that has an abrasive stone spinning in the center and a scarified metal screen on the outside. (The abrasive system). The rice then passes through a milling chamber that has a metal roller spinning in the center and a scarified metal screen on the outside. This machine is rubbing the many kernels of rice against themselves and the screen in order to remove the bran. (The frictional system.) The last pass (sometimes all frictional passes) is basically another frictional machine that is applying a mist of water to facilitate milling and add a smooth polished surface to the rice. (The water polishing system.) This Japanese system can be done in three passes as described here, or as many as seven passes.

			Broken Removal. Milling the rice can yield as many as 4 to 40 percent broken kernels depending on the quality of the incoming rice and the milling equipment. Most high quality rice is sold with less than 4 percent brokens and so brokens must be removed in the milling process. The rice is passed through indent graders. These can be cylinders with small pockets too small for whole grain to fit into, but just right for brokens, or disks within a trough that have similar indents. Either way, the idea is for the brokens kernels to temporarily fit into the indent so that they will be picked out of the whole kernels and then thrown into a separate flow. The brokens can then be passed over screens or additional indent graders to be further separated into various sizes. (brewers, screening, and second heads).

			Sorting. The milled whole kernel rice is passed through an electronic sorter to remove defects. The rice is passed before an electronic eye that detects any difference in color. A jet of air removes defects. Usually damaged kernels (with black specks), yellow kernels, and stones are removed. The very best mills pass the rice through two breaks of sorters. Sorters can be adjusted to remove green immature kernels from brown rice, chalky rice from white (more translucent kernels) rice, or regular medium grain rice from chalky mochi rice. There are special sorters to remove glass from rice.

			Magnets. There are usually magnets throughout the milling system to remove metal that can damage machinery and get into the rice. Many have a non ferrous metal detectors (can remove all metal including aluminum and stainless steel) just before packaging as a final safeguard.

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