Advances in maize processing

by Peter Striegl
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Approximately 2.2 billion tonnes of grain is produced worldwide each year, with maize (corn) accounting for 32% of that total.

Higher yields are occurring thanks to modern cultivation technology, the breeding of new maize varieties and the use of fertilizers. These factors have also led to increased cultivation in areas that were unsuitable for growing maize in the past.

Maize has been used for animal feed for many generations and continues to be utilized in many different ways for human consumption. It can be found in everything from tortillas in Mexico and Central America to maize meal in southern Africa and polenta in Europe. Furthermore, maize is becoming an important raw material for ethanol production.

Thorough studies also have been conducted on the industrial production of this basic food in order to facilitate its use or preparation in the processing industry as well as in households. These studies have been expanded to create new maize-based products, with special attention being given to possibilities of reducing the preparation time in maize dishes.

KERNEL CHARACTERISTICS

The hundreds of maize varieties are divided into groups according to specifications such as the structure and shape of the seed. Regarding hardness and size of the kernel, the hard and smaller grains are more often found with the flint variety (e.g. Plata maize), whereas the endosperm of the dent variety (e.g. yellow maize and white maize) is generally softer and partially floury.

The size of the germ is generally larger in dent maize. The vitreous kernel generally renders a higher yield of grits and a lower yield of germ than the softer, floury dent maize. Therefore, the type of maize chosen is predetermined by the finished products.

The structure of the kernel helps determine the technique used to process maize. When finished products with low fat content are required, the germ and the pericarp, both of which have a high fat content, have to be properly removed in the process.

An important factor in the production of low-fat finished products is the endosperm’s fat content, which varies depending on the variety of maize. In the maize milling industry, the flint and dent maize varieties are most commonly processed. In addition to having a variety of kernel characteristics, the color can be different from one type to another, ranging from white, yellow, red and purple to black.

The grinding systems have a significant impact on the quality and yield of the finished product. Consequently, when designing an industrial plant, the  main products from the maize degermination and milling process have to be specified. Furthermore, some downstream processes, such as the production of arepa and tortillas, have specific processing requirements.

The products from the maize mill are basically classified in four categories: flaking grits (coarse), brewer’s grits (medium), snack grits (fine) and maize meal.

CLEANING

The separator, with aspiration channel, and the destoner are the main machines in a maize cleaning system. With the installation of a combinator instead of a destoner, the maize will be additionally classified and a major part of the “cobs” and other light impurities can be separated. If there are special requirements of the end product, such as minimal fragment count, or if there are problems regarding aflatoxins, a scouring machine with an attached aspiration channel can be installed.

It is important to avoid fluctuations in the moisture content of maize and obtain a stable moisture level in the end product. One way to accomplish this is to use the Aquatron, an automatic moisture control device in which the moisturizing occurs by means of a special dampening screw.

DEGERMINATION

The new, patented MHXM degerminator is one of the latest advances in maize degerminating technology. It simultaneously separates the germ and removes the pericarp, achieving unique results in low-fat and high-purity finished products.

The maize is fed by the intake screw into the processing zone, consisting of a drum rotor and a specially structured screen jacket. A high degree of degermination and dehulling will be achieved through the intensive processing between drum rotor and screen jacket as well as by the corresponding adjustment of the retarding device in the outlet of the machine.

Advantages of using the new high capacity, easy-to-operate degerminator include:

• High yields of finished product with low fat content;

• Simplified process;

• Low production costs;

• Quick and easy changing of worn parts.

 

MILLING

In recent years, Buhler AG has developed a specific processing technology for the maize milling industry. It covers  solutions for a whole range of products including flaking grits, brewer’s grits and snack food grits, as well as maize meal and plants for the starch, ethanol and germ oil industries.

The new technology with the maize degerminator MHXM simplifies the milling process by reducing the amount of equipment needed, resulting in low investment and operating costs.

After the degermination, the endosperm is refined and calibrated to reach the desired finished-product specifications. This is done on the Newtronic roller mill and Sirius sifter. The aim in producing grits is to calibrate the endosperm precisely, with the least amount of fines. This is achieved with a stable roll setting and adequate roll corrugation (fluting).

Special attention is given to the sifting process. Since the maize meal has sticky properties, efficient sifting is of the utmost importance. This can be assured by equipping the Sirius sifter with the NOVA sieve generation. The interaction of the higher dynamic force and the NOVA sieve cleaner assure best sifting with long availability of the sieves. Furthermore, all surfaces in contact with the product are of stainless steel or special synthetic material to avoid buildup of product.

The degermination process and the grinding technology must be designed for the specific finished product required. Brewer’s grits, snack food grits and maize meal can be produced on a dry degermination and milling process, achieving high extraction rates on products with a fat content of less than 1%.

For the highest possible yield of flaking grits, a hard type of maize must be used. With the latest Buhler degerminator, including a special preparation, screw flaking grits with extremely low fat and fiber content are achieved.

If there is a specific request for germ recovery, the degerminator can recover 8% to 14% germ with a fat content higher than 20%

To produce products for starch factories and ethanol plants, a dry degerminating process is used. The milling process is reduced to the maximum just to achieve the granulation required.

The introduction of the new technology of degermination and dehulling is considered an important change in maize processing. Higher yield of low fat products with less production costs has significantly improved the total cost of ownership for the maize milling industry.

Peter Striegl is a technologist for Buhler AG, Uzwil, Switzerland. He can be contacted at  peter.striegl@buhlergroup.com

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