More than Chicken Feed: Milling Maize for Food Products

by Teresa Acklin
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Part 1 of 2 explores the milling and baking characteristics of maize.

By Mario Cinquetti

   Maize is a versatile grain. In addition to its various end uses, maize can be cultivated systematically in tropical countries where wheat grows with difficulty. Because of this characteristic, maize is the most widespread cereal cultivated in Africa, and its use for human consumption largely surpasses that of wheat, which, in most cases, must be imported.

   In fact, the basic foodstuff of Africa is maize mash, often called polenta, although the name changes from country to country. Hundreds of industrial milling plants, more or less updated, grind maize in Africa, as well as in other areas, especially South America.

   The trend of maize consumption is increasing, and African mills will have to diversify in order to expand their economic results in the face of increasingly seasoned competition and the variable needs of the market. Modern maize milling also is of interest in Middle East countries, which today are importing considerable quantities of maize grits.

   Today, mill diversification is feasible thanks to advanced technologies, which enable production of maize flours for bread, biscuits and pasta; brewery grits or grits for snack food; hominy grits for corn flakes; germ from which salad oil is obtained; and the traditional semolina for polenta.

   Three products are of particular interest to African and Middle East millers: fine flours for blend bread, pasta or biscuits; grits for the production of snack food; and brewery grits.

Maize Bread Flour

   The ideal flour for bread use is wheat flour because it enables good fermentation of the dough, an exceptional increase of volume with a soft structure and the transformation of its components — especially starch — into a tasty food that is easy to digest. But maize flour, well degerminated and refined, with fine granulometry and a low fat and acid content, mixes well with wheat flour in the dough phase.

   Maize flour mixed with wheat flour is used in many South American and African countries. Bakers in Italy, France, England, Yugoslavia and Germany also have produced bread from mixed flours during wartime or famine periods, and specialty breads with maize flour currently are produced in some European countries. Specialty maize foods also are produced in other areas, such as regions of Italy where there is a secular tradition of maize food cookery.

   But maize flour's baking characteristics differ from those of wheat flour, requiring some adjustments. For example, test baking shows that if maize and wheat flours are mixed in equal quantities, the bread dough subsides during the first period of cooking. This occurs because maize flour's elasticity and cohesion are not sufficient to resist the gas pressures developed by temperature during rising.

   Because this effect damages bread quality, smaller quantities of maize flour, from 10% to 15% of the weight of wheat flour, are employed. For Arab- or Indian-type bread, which does not require long fermentation times and significant volume increase, maize flour can be used in a 20% to 25% proportion.

   We should note that the sugar content in maize flour is higher than in wheat flour; consequently, the taste of bread from mixed flour is improved. Also, the crust develops a browned color, as if coated with burned sugar, a characteristic that is appreciated by consumers because of its similarity to homemade bread cooked in a wood oven.

   The fat content of maize flour used for a maize/wheat bread flour mix should be less than 1.5%; a higher content has a negative effect on the coloring, taste and volume of bread and is adversely affected by hydrolysis.

   In general, a good maize bakery flour should have 3% maximum acidity, 0.60% ash content, granulometry of less than 220 microns and a fat content not exceeding 1.5%.

Maize Flour for Biscuits and Pasta

   The basic ingredient in biscuit production is wheat flour, and the most suitable is soft wheat flour with 7.5% to 9% protein and soft gluten, which is difficult to find in the market and therefore rather expensive.

   To reduce raw material costs, biscuit manufacturers commonly use average bakery flour, with 10% to 11% protein, mixed with maize flour, maize starch or potato flour to reduce the protein content. Maize flour is preferred by biscuit makers because it not only balances the wheat flour protein content, it also makes the biscuit more friable and crisp.

   Italian millers supply maize flour for biscuit production with granulometry of less than 220 microns and a fat content of up to 2%. In common dry biscuits, maize flour is used in a 10% proportion; in tea or pastry biscuits, the proportion can reach 20% to 25%.

   Maize flour was not used for pasta production until the 1940s, when Italian millers attempted to make pasta with half wheat and half maize flour. Because of the war, experiments with alternative food products were not uncommon.

   The results were not satisfactory because the two flours required different cooking times. Six to seven minutes were insufficient for maize flour to cook, resulting in sticky pasta; but the 12 to 15 minutes needed for maize flour were too much for wheat flour, resulting in a huge starch loss and slimy pasta. Moreover, wheat/maize pasta tasted different because of the high degree of acidity in the maize flour, which was not well degerminated.

   But the solution to the "maize pasta" problem did not depend on the variation of processing methods or of cooking times, but on the use of white maize gelatinized flours that were very well degerminated. In fact, only at the end of the 1960s was it possible to produce 100% maize pasta with the same processing lines for wheat pasta by using pregelati-nized maize flour.

   With good color, appearance, taste and a smooth surface, maize pasta loses negligible quantities of starch during cooking. The difference between durum wheat pasta and maize pasta cooked with the same sauce also is negligible. And maize pasta does not become either slimy or sticky, problems that can arise with pasta made from non-durum wheats.

   In addition to using 100% pregelatinized maize flour, pasta producers in many countries use 80% to 85% non-durum wheat flour and 15% to 20% fine maize flour, not pregelatinized, with acceptable qualitative results. The non-pregelatinized maize flour must have a fine granulometry of less than 250 microns, 1% fat content on a dry matter basis, 0.5% cellulose and 0.60% ash content.

Maize Brewery Grits

   In brewery processing, only the vitreous fraction of maize is used because it contains a high concentration of starch from the caryopsis and a fat content of less than 1%, dry matter. Granulometry can change from country to country; in most cases, it ranges from 250 to 1,360 microns. The accompanying table outlines milling results for grits, based on three main types of maize degerminators.

   The fat content of grits must not exceed 1% to avoid producing a light colored beer with thin foam and poor taste. Some maize mills also guarantee the content of extracts, which can reach 89% from U.S. No. 3 yellow hybrid maize and 87% from Argentine vitreous Plata maize.

   In factories that process a blend of 70% malt and 30% maize or rice, about 16 kilograms of dry matter produce 100 liters of beer with 11° saccharometric, and 18 kg produce 100 litres of special beer with 14° saccharometric. Considering that average moisture is 14%, we need 16.8 kg and 20.9 kg of raw cereal to produce 100 liters of beer with 11° and 14° saccharometric, respectively. Therefore, 5.04 or 6.27 kg of maize grits are needed if the blend contains 30% of raw cereals, or 8.4 or 10.45 kg of grits with blends of 50% raw cereals.

   Brewery factories have tended to increase the maize fraction for economic reasons, and brewers in many countries use maize grits for up to 50% of the raw materials blend.

Snack Foods and Germ

   Snack foods such as corn curls, corn collets and expanded products, are obtained from maize grits of 500 to less than 1,000 microns with low fat content of 1%, dry matter. These foods have different shapes and are flavored with seed oil, paprika, salt, cheese, tomato, nuts, chocolate or other ingredients.

   Snack foods are processed by an extruder, which, to produce 100 kg per hour of expanded product, requires a 30-kilowatt motor. The extruder is served by a set of ancillary equipment including a measurer, an ingredient mixer, a drying oven, a rotary drum to spray the seasonings and a packing line.

   Before entering the extruder, the semolina is suitably dampened. The moistened starch cells come under pressure from the extruder screw and heat in the machine; when the product is discharged through the die-plates (with different geometric features to obtain variable shapes and sections), the extreme pressure difference causes the product to "burst," increasing volume by five to six times.

   The expanded products are used as aperitifs and snack foods, in soups, as breakfast food, and in many countries, are used to produce corn flakes. When appropriately ground, expanded products can also be used as baby food flours.

   Expanded product yields are about 10% less than those for brewery grits as shown in the table because these products must be refined further and they lose the fine fraction lower than 500 microns.

   Maize germ is one of the most valuable components of the caryopsis and is used in the production of salad oil and cake with high protein content.

   About 10 kg of germ with 21% to 23% oil content can be produced from 100 kg of dry degerminated maize. With a solvent extraction oil mill plant, 10 kgs of germ yield 1.9 kg of oil; continuous presses or "expellers" yield 1.5 kg of oil.

   Maize oil is considered high quality because it is an important source of unsaturated fatty acids. In cooking, this oil is largely used to dress salads, fry foods, make mayonnaise, etc. It is also used in the production of margarine, as a vitamin and medicine base in the pharmaceutical industry and to improve the quality of other seed oils.

   This article is based on a presentation by Mario Cinquetti, sales director with Braibanti Golfetto, Padova, Italy, at the 8th annual conference and trade show of the Association of Operative Millers, Middle East/North Africa District 16, in Luxor, Egypt, in November.


Analysis of brewery grits (U.S. No. 3 yellow maize)


Type of degerminator

Component percentage




(dry basis)

(45% yield)

(53% yield)

(58% yield)

























   * after adequate drying