Rice Quarterly: New rice milling technology gaining acceptance in South America

by Emily Wilson
Share This:

Rice that is grown in the tropics of South America usually has lower total yield (polished grains, whole and brokens), lower head yield (whole, non-broken grains) and higher contents of chalky and white bellied kernels.

These chalky areas, besides affecting the appearance of polished rice, form weak spots, which during the drying, husking and whitening process result in increased kernel breakage.

Lower price margins, driven by market globalization forces, has enabled the region’s rice milling industry to install and apply technology that can increase total yield and head yield.

The most modern rice mills are equipped with the latest hulling and whitening equipment manufactured in Germany, Japan and Switzerland, as well as high-quality rice milling equipment manufactured in the region, especially in Colombia.

During the El Niño weather phenomenon in 1998, many countries in South America had to import paddy rice, mostly from the United States. Milling experience with the imported rice showed that the hard kernel, high-quality grain produced higher head yields, sometimes two or three points higher than those obtained with the standard McGill probe rice mill used by the U.S. Federal Grain Inspection Service (FGIS). The McGill mill produces head yields that reflect technology similar to that used by U.S. rice mills in the mid-1970s.

Tropical rice varieties have a higher content of weaker, chalky kernels. The longer flowering periods of most tropical rice varieties may induce the presence of over-dry and immature grains during harvest.

In a recent analysis of Venezuelan rice, using a Single Kernel Moisture Tester, a sample of fresh harvested rice had an average moisture of 23.4% and included kernels with moisture as low as 17.5% and as high as 28%. The standard deviation statistic was 2.46, showing, on average, a high moisture dispersion. Another sample with average moisture of 25.4% included kernels with moisture as low as 19% and as high as 33%; the standard deviation was 2.58.

The typical tower rice drier cannot reduce the dispersion to figures lower than the standard deviation of 1.00 and typical short-term storage of 15 to 30 days is not enough to further reduce dispersion figures.

Paddy arriving at the mill may have moisture ranging from 8% to 14%, the average being 12.5%. Over-dried kernels produce unnecessary weight loss, and high moisture kernels may have difficulties in the breaking, husking and whitening processes.

Several applied research projects are now pursuing ways to reduce moisture dispersion figures that affects shrinkage and milling yields.

In some countries, rice is customarily harvested with average moisture contents ranging from 20% to 24%. The Colombian rice industry has established the minimum moisture content of grain from the field at around 21%. Colombian rice millers visiting U.S. rice-growing areas are surprised at the lower moisture content of its harvested rice.

In Venezuela, it is customary to receive rice from the fields with 17% to 18% moisture, but it has been demonstrated that head yields are reduced due to sunchecking suffered by grain.

When I was a young engineer in training, I recall that in the U.S. in the mid-1960s the typical rice harvesting moisture content, in order to get best head yields, was 20% to 22%. U.S. rice varieties have been modified over the years and new ones are able to withstand sunchecking stresses produced by delayed harvest. But in rice varieties grown in central and northern South America, this resistance, until recently, has not been particularly sought by breeders. The Irrigated Rice Latin American Fund has introduced the concept of delayed harvest resistance.


To be able to analyze and understand kernel breakage that occurs during the milling process, some new concepts have been introduced to the region. These concepts gradually have been gaining acceptance.

To have a baseline for grain received from field, the newly adopted procedure involves drying a sample with a low temperature laboratory drier, husking by hand samples of 100 grains and counting the number of brokens and severely fissured kernels. Samples with less than two broken kernels are qualified as high milling quality and normally yield more than 58% of head rice when milled in the McGill unit. Samples with two to four broken kernels may yield about 54% of head rice, and samples with more than four broken kernels are regarded as medium or low quality.

The second concept is the use of the McGill test mill as a guide or predictor of head yields to be obtained in the industrial mill. A technologically advanced mill should obtain about 2% more head yield when milling good quality rice. This difference is greater with medium quality grain.

In Colombia, the largest rice-producing country and consumer in the region, gross margins (defined in this case as total sales, in small bags of 1 kg to 5 kg, over paddy rice costs) have been reduced gradually to 20% or 21% in recent years from 26% to 30% obtained in the 1970s and 1980s. These lower margins have enabled Colombian rice millers to reduce costs, increase head yields and recover all small pieces of brokens.

In Venezuela, gross margins until a few years ago were between 35% to 40%, and the need to reduce costs and increase yields was not as great as in Colombia. Currently, lower margins are allowing companies to install new rice milling machines and have paved the way for new and more stringent standards.

In all mills, husks are removed with rubber roll units. New European and Japanese huskers that use specially designed feeding systems obtain rates of 4 tonnes of paddy per hour (hulling 92% to 94% of husks), compared with 5 or 6 tonnes per hour obtained with U.S. paddy.

Paddy separation is accomplished in modern mills in Colombia with table-top units, which have just two lines — one of separated paddy and the other of cargo, or husked, rice. It is common to observe a unit working for hours with no more than two or three paddy kernels per kilograms of cargo rice and small amounts of cargo kernels in the paddy side.

In other countries, especially in Central America and Venezuela, the tray Asian-type separator is widely used. This unit has three lines of products: one of paddy, another of cargo, and a third of mixed products. The table-top separators are not only more efficient but, with the development of machines with more decks, also save space.

It has become a widely-used practice in modern mills in Colombia and Venezuela to install precision width graders in lines of cargo rice, to separate the red rice grains (a problem in all countries as red rice kernels are usually thicker than common white rice), paddy kernels, large stones and clumps of dirt.

Some mills have tried to separate broken grains in cargo lines in order to polish only whole kernels of similar thickness, avoiding smaller pieces that may act as a kind of wedge. However, results have not been conclusive.

Selection of whitening and polishing equipment, in the past a matter of price, now includes the analysis of country price differential between whole and broken kernels.


Colombia is the largest rice producer in the region. Production in 2001 is estimated around 2.3 million tonnes of dried paddy. Due to limitations of foreign investment and a clear import policy followed since World War II, it used to be very difficult to import any type of milling machinery in Colombia.

The country developed a relatively strong grain and rice equipment manufacturing industry that supplied not just the domestic market but other countries in the region as well. Several manufacturers thrived in the cities of Barran-quilla, Armenia, Ibagué and Bucara-manga.

Colombia inaugurated a policy of commercial openness in the early 1990s, and the government reevaluated in real terms the currency from 1990 to 1997. The resulting loss of competitiveness in a few years decimated all segments of industry, including rice milling equipment manufacturing. Only one manufacturer has survived in good shape. Its success is explained by an export-oriented attitude, an effort to modernize in all aspects, and its seaside location.

Today, the leading rice millers in Colombia import most of their machinery from Japan and Europe. Mid-size mills use Colombian versions of imported machines, manufactured in small shops that serve local markets.

Of the 60 or 70 rice mills operating in Colombia in the early 1990s, the most successful upgraded their equipment during that decade, especially in the husking, polishing and color sorting areas. Drying technology changed little, using the same system of pools, sometimes combined with tower driers, developed in the 1970s and 1980s.

The five or six largest Colombian rice mills can process nearly 50 tonnes per hour, using three whitening/polishing passes, usually one abrasive unit followed by two friction units.

The abrasive unit removes 60% to 70% of bran, producing fewer brokens but leaving some scratches on the rice surface. The friction units inherently produce more brokens, and are used for removing the final layers and lines of bran and for correcting scratches.

The last polishing pass uses small amounts of water to form, with the last remnants of bran oil, an emulsion that plasters and covers scratches, giving kernels a shiny appearance.

The next largest group of rice milling companies, comprising 12 or 15 mills with capacities ranging from 20 to 40 tonnes per hour, also use three passes in the whitening/polishing process.

At least 80% of the rice produced in Colombia is sold in small packages, from 1 kg to 5 kg. Practically all packaged rice has been color sorted with machines made in Japan, Europe, Brazil, and, very recently, Korea.

Parboiled rice is not a large sector in Colombia. Currently, only one plant operates, using typical U.S. technology. Two other plants were opened and closed in the 1980s.

Colombia’s continuous search for ways to avoid lost grain and reduce brokens has become the model being adopted in other countries.

Induarroz, the rice millers’ federation, is an active organization that represents millers in government and international negotiations, and acts as a "think tank" and forum for matters of interest to the industry, such as marketing, technical and financial

Induarroz organizes an annual conference that has become the most important event for the industry in the region. Its commercial exhibition usually includes 15 or 20 booths of rice milling equipment manufacturers and service providers.

Rice growers in Colombia are organized in Fedearroz, a strong federation that participates directly in rice breeding research. In recent years, Fedearroz has developed four rice varieties that have produced good results in the field and in the mills.


Peru’s coastal areas produce a high-quality milling rice. Total production of paddy per year is around 1.6 million tonnes, and very high milling yields are obtained.

For several decades, government agencies bought most of the paddy rice and contracted with private mills to mill the rice. Margins were low and controlled by the government. This procedure was replaced some years ago by a free market scheme, but the Peruvian milling industry is small and technologically less advanced than the industry in Colombia and Venezuela, despite the magnitude of its paddy production.

What could be considered a large rice mill in Peru may process 10 tonnes of paddy per hour. Some millers are installing newer rice milling technology. Only a few color sorters have been installed, but rapid development of the packaged rice industry promises a growing market for this technology.

No parboiled rice is produced in Peru. Small amounts of parboiled rice are imported from Brazil and Uruguay. Consumer preference in some Andean areas for colored rice (stained by heat damage) may open up opportunities for production of this type of rice.

Peru’s rice millers association, Apema, is still small but is starting to grow. Most of its activities are linked to government negotiations but its participation in other areas has been increasing.


Ecuador is the third-largest producer of paddy rice in the region. Production approaches 1 million tonnes of dry paddy annually.

Ecuador’s milling industry is primarily composed of several hundred small mills of very low capacity (a few tonnes per day). Only 20 or so mills could be considered modern and organized. A large mill in the country may process 10 tonnes per hour.

The people living in the Andean mountain area have a preference for lightly heat-stained rice. Consumers enjoy the distinct flavor, smell and texture of this rice. Heat-affected rice may be considered aged or matured grain, with better cooking properties.

Parboiled rice has found a natural niche in this market. There are three or four small plants, not too sophisticated, in Ecuador’s coastal areas.

Another product influenced by the preference for stained rice is artificially aged rice, produced with temperature controlled systems. This "envejecido" (aged) rice has what is regarded as better cooking properties in volume, taste and flavor, and brings a premium price.

There is no formal association of rice millers in Ecuador. Several groups of mills participate in negotiations with government or with international organizations.


Venezuela is fourth-largest rice producer in the region, its production currently around 600,000 tonnes of paddy per year.

Higher price margins has enabled mills to indulge somewhat in the search for increased head yields. Until very recently, most rice mills used a Mexican-made, single-pass whitener/polisher — a good energy-efficient machine but one that resulted in 2% to 3% more brokens over a three-pass process with good quality rice. This difference may augment to 5% or more with lower milling qualities grains.

In recent years, price margin pressures have given millers an incentive to install the latest model huskers to replace tray separators with table-type paddy separators, and to install three or four passes of whitening lines. Color sorters are still a novelty but are being installed at rapid pace.

In the 1980s, for marketing reasons, the leading mills introduced premium quality brands having less than 3% brokens. These premium brands occupied a large area of the market and mills, with a low recovery of head yields, had large surpluses of low-price brokens. Current economic difficulties have produced brands with contents of 10%, 20% and even 30% brokens.

The main role of Venezuela’s formal rice millers association, Asovema, has been to conduct negotiations with government and rice growers. Some years ago, rice millers and growers organized Fundarroz, an organization that primarily funds rice breeding research. With the support of international consultants, Fundarroz also has encouraged the milling sector to reduce price margins, save broken kernels and recover the lost grain.


Panama has the highest per capita consumption of rice in the region. The milling industry operates, with some exceptions, rather old fashioned units of reduced capacity. A large mill in the country will process about 10 tonnes per hour.

As the country harvests just one main crop per year due to lack of irrigation, it is necessary to store grain for much of the year, which is difficult in a tropical climate with high temperature and high humidity. Several rice mills in Panama have installed, with good results, cooling units that reduce insect activity and prevent mold development.

Most mill diagrams follow old designs, although a few have incorporated destoners and precision width graders to separate red rice, paddy and small dirt balls.

The Association of Rice Millers in Panama is involved in government negotiations and information gathering.


Guatemala, along with El Salvador, has the largest per capita consumption of parboiled rice in the region. The success of parboiled rice in this country can be traced back to the 1950s when a large part of paddy was not dried on time and the rice became stained by high temperature and mold. Consumers became used to and fond of the distinct flavor and odor of the stained rice.

This same situation occurred in many other Latin American markets. In Colombia, many consumers called the heat-stained rice "llanero," meaning rice produced in the flat eastern prairies where little drying capacity was available. "Llanero," or stained rice, disappeared in Guatemala in the 1960s with the installation of drying units.

Parboiling plants were installed in Guatemala and El Salvador in the 1950s. The product resembled the uniform heat-stained rice and the market welcomed the newcomer.

Arrozgua, a relatively new organization of millers and farmers in Guatemala, is involved in government negotiations but also promotes technological development among millers and farmers. Arrozgua in early 2002 will have in operation a new central laboratory equipped with FGIS-approved equipment.