maize processing

Maize Processing – Equipment, Processes, Products

Maize processing is a very significant part of grain industry. Maize (or corn) is a raw material for various other products. Corn processing results can vary between corn starch and popcorn, polenta and bourbon. This article gives you a good overview about maize processing industry.

Corn is one of the most important cereals, widely cultivated in tropical and temperate regions. In fact, it represents just about one-third of the world’s cereal production. Corn originated from Latin America and was introduced to Europe only after the discovery of America.

Among all agricultural raw materials, corn is the one that, more than any other, has been able to adapt to different agrarian environments. It represents an irreplaceable source for direct use and industrial transformations.

The changed primary food needs, the development of new knowledge in the chemical and microbiological field, and the acquisition of increasingly sophisticated industrial technologies have made it possible, starting from the mid-1800s, to look at corn as the privileged material for industrial use.

The range of products obtained by processing corn dry (mills) or wet is extensive. We get more or less fine broken pieces, semolina, flour, and bran through dry processing. Flakes, polenta, pre-cooked flours, gluten-free semolina, etc., are produced with the flours.

maize processing

From wet processing, first transformation products are obtained: native starch, proteins, gluten flour, and corn steep liquor (a protein concentrate resulting from the lactic fermentation of corn).

Subsequently, using starch as raw material in a cascade process, second transformation products are generated: dextrins, glucose, dextrose, fructose, isoglucose, caramel, pregelatinized starches, modified starches, cyclodextrins, polyols, and organic acids.

Maize Processing Equipment

Example machines used for maize processing:

Corn Cleaning Machine

The cleaning phase is essential to reduce the bacterial load and the possible presence of molds and toxins if any. In this machine, the corn undergoes the following cleaning treatments:

  • Separation of light and semi-empty parts, complete with cyclone decanter and large plex tube to have an immediate view of the separated elements;
  • Calibration from which all the foreign bodies present in the grain with smaller size are eliminated in the first sieve;
  • Second calibration from which all the foreign bodies present in the grain with a larger size are eliminated in the second sieve;
  • Magnetic separation of ferrous metal bodies;
  • Drum separator for the round extraneous seeds and the broken grains.
  • Grain brush for rubbing the grain and removing dust or earth that adheres to the grain
  • Washing the cereal in a counter-current of air removes any dust.

Degerming Equipment

  • The machine breaks the corn seeds into pieces by detaching the vitreous part from the germ.
  • The hardest part of the grain breaks, while the softer germ is less damaged.
  • The broken product exits through the output channel and falls on the lower hopper. Any foreign bodies, if present, come out in the second exit of the machine.

Milling Machine

  • The product is processed through the mill to obtain corn flour

Corn Starch Production

The maize processing technique for starch extraction has been known since ancient times when farmers obtained it from a mixture of wheat and barley flour. The discovery of papyrus sheets from ancient Egypt traces the use of starch back to 3500-4000 years before the coming of Christ: at that time, rice and wheat were widely cultivated. They were used as food for humans and for technological uses. 

maize processing

Nowadays, starch is also being produced from corn. You can obtain corn starch from corn through a wet grinding process. The product physically comes in poor white color, insoluble in cold water. Dispersed in cold water and boiled subsequently, it swells with the formation of a paste.

What is the difference between corn starch and corn flour?

Corn flour is produced starting from the grinding of the whole grain: endosperm, germ, and bran parts. On the other hand, only the endosperm is used for corn starch.

While you can produce corn flour through dry grinding, corn starch is produced through wet grinding, which leads to the formation of a white, almost impalpable powder.

We will discuss the wet milling process a bit later. Still, in short, to produce corn starch, the corn kernels are placed in a solution with sulfur dioxide, then ground in several cycles. A compound is thus obtained from which a centrifuge machine can separate the starch. We then proceed with the drying and powder reduction.

Now, let’s take a closer look at the details of the industrial maize processing using wet milling.

The industrial process of wet corn milling

Wet milling (also called wet grinding) is a process that requires a solid supply of energy with a lot of water added at each step. Wet grinding, therefore, is a costly process from a resources point of view. You can even find calculations that about ten calories of fossil fuel are burned for each calorie produced.

So, what’s the purpose of this process? The grains are separated into their physical components, i.e., germ, endosperm, fibers, and, later, into the chemical elements:

  • First, when a batch of corn arrives, it is kept for 36 hours in an acid bath made of water in which a small amount of sulfur dioxide is diluted. This makes the grains swell and free the starch from the surrounding proteins.
  • After the bath, the grains are crushed into a soft, wet, shapeless mass by a grinder. At this point, the germ has become rubbery and comes off easily.
  • The paste that comes from the grinding goes into the hydrocyclone, which is basically a centrifuge for liquids. The germ separates and rises to the surface because it floats. It is collected, dried, and squeezed to obtain the oil. Corn oil is used directly in cooking, frying, and seasoning or is hydrogenated and becomes margarine or enters various packaged foods.
  • With the germ removed and grains crushed, the so-called mill starch remains, the white pulp of proteins and starches in aqueous suspension. Suppose you want to extract the starch in more significant quantities. In that case, your manufacturing process must go through a series of increasingly more fine grindings, filtrations, and centrifuges. The protein extracted in this way is gluten, used in animal feed. 
  • At this point, a white slime remains, which is poured onto a steel plate and dried. The result is an impalpable white powder: natural corn starch.

What Else Can I Get From Wet Milling Process?

Sweeteners quickly became an essential product. Corn syrup, mainly made of glucose or dextrose, the terms are synonymous, was the first cheap substitute for cane sugar.

In fact, scientists discovered that an enzyme, glucose isomerase, was able to transform glucose into the sweeter fructose. Over the years, the process was perfected. It became possible to market corn syrup with high fructose content or, more briefly, HFCS, a mixture of 55% fructose and 45% glucose, exactly as sweet as sucrose, white sugar, so to speak. Today it is one of the most popular products of corn processing.

HFCS. Is there something more?

In fact, a lot. The white starch mass is separated and divided at the various process points into different paths. The starch can be modified to create spherical, crystalline, or branched molecules. Each serves a specific purpose: it can become an adhesive, paint, glue for industry, or a thickener, gelatin, and stabilizer for food.

The final residue of the pulp is ‘saccharified’, treated with enzymes to obtain a dextrose syrup. A part of this, the most consistent, is tapped. Other fractions will instead become maltodextrin and maltose.

The tapped faction is placed in a reservoir, exposed to the action of glucose isomerase, and then passed through ion exchangers to become fructose eventually.

Finally, the remaining part of the dextrose syrup is placed in tanks for fermentation, where various yeasts and amino acids are put to work. After a few hours, they transform the sugars into an alcoholic mixture. This mixture, in turn, is fractionated into various alcohols, especially ethanol, the car fuel and the final destination of about one-tenth of all corn.

The same alcoholic mixture can be refined and provide dozens of other organic substances used in the food or plastics industry.

And it all ends here, it would seem, the corn has disappeared, and there is not much left, if not a little dirty water. However, part of this so-called steeping water can be used to make feed for domestic animals.

In short, this industrial refining called wet grinding, different from the dry one from which, for example, the flour is extracted, practically does not produce waste.

Products From Maize Processing

In addition to being an essential element in animal feed production, corn also enters the food industry as raw material in the form of various products. With corn flour, it is possible to prepare polenta, pasta, biscuits, crackers, and other baked goods.

You can obtain popcorn, crackers, and corn flakes from the whole grain of corn. You can make corn porridge, also called grits, out of corn after the grinding. Corn is used for the production of alcoholic beverages too. Finally, you can extrude oil from the corn germ, which is very popular for its nutritional properties.

Now let’s take a closer look at some of the corn processing products.

Polenta

In some regions, this food has been the basis of the peasants’ diet in the past. The improvement of living conditions has led to a drastic reduction in the consumption of polenta, almost transforming it into a gastronomic specialty, often combined with meats, cheeses, and mushrooms.

polenta maize processing

On the market, there are three types of flours obtained from the dry grinding of corn, different in terms of grain size: 

  • the coarse flour, which is suitable for getting delicious polenta
  • the medium ground flour, containing fine/medium granules for soft and delicate polenta
  • the most refined flour, ideal for the production of sweets and biscuits.

Corn Spaghetti

Corn spaghetti is mainly intended for those who are intolerant to gluten. Other bakery products can be prepared using the finest corn flour, in particular, crackers, biscuits, or bread. However, these products require the addition of a certain percentage of wheat flour to process the dough.

Corn As a Side Dish

Corn can also be used as whole grains, steamed, and eaten as a side dish or in salads. Whole grains can also be boiled or roasted, but this use is not very common.

Popcorn!

This is something everybody likes, isn’t it? You just need to choose particular corn varieties with higher protein content than normal ones. Following the heating of the seed, the water inside the starchy endosperm evaporates but remains trapped by the impermeable layer of the pericarp until it reaches certain pressures and very high temperatures (350° F).

The starch also swells and presses from the inside until the wall of the corn gives way, exploding with the release of the gelled starch. This food is very popular in the United States, where there are famous chain stores dedicated to popcorn with many variations of flavors. Therefore, a real popcorn business can be created here: from weddings to corporate events, from decorations to parties.

Corn Biscuits

A process similar to that for the production of popcorn is used for the production of biscuits, used as a substitute for bread in many diets.

The corn kernels are placed in molds of a specific shape and closed, then brought to a temperature of 392° F and subjected to very high pressure. When the molds are opened, the corn kernels explode, releasing the starch within them; the grains, joining together, form the biscuit.

Corn biscuits are very dry, crunchy, and full of air, similar to puffed rice. Some biscuits are flavored with salt, which is added before production. Still, others are flavored with aromas.

Corn Flakes

Corn flakes are a food consisting of corn cooked with sugar and vitamins. The corn kernels, especially those of yellow corn with vitreous endosperm, are steamed, crushed through a roller press, and finally dried.

They are typically eaten for breakfast and served with milk. Corn flakes were invented in Michigan in 1894 by the Kellogg brothers. Later, given the success of this preparation, the production of flakes was also tested with other cereals. 

Spirits

A product of the dry grinding of corn is grits, a coarser ground corn kernels. Grits are used to ferment alcoholic beverages because they represent a good source of fermentable carbohydrates. Beer, vodka, gin, and bourbon are drinks, that can be made from corn.

Starch 

As previously described, starch is extracted from corn and used for other industrial and food preparations. You can use it as it is after drying (native starch) or modified by chemical, physical or enzymatic treatments. By acid or enzymatic hydrolysis, glucose, dextrose, and fructose syrups are obtained and used as sweeteners, a source of fermentable sugars in the food and pharmaceutical industry.

By heat treatment in water and subsequent drying, gel-like starch is obtained, which is used in the food sector (to give consistency and viscosity to instant preparations such as puddings, sauces, or soups).

Corn germ oil

Last but not least in this review is corn germ oil. The oil extracted from corn germ has a straw yellow color due to carotenoids, a delicate taste, and a high content of essential fatty acids; it is also rich in vitamin E.

Corn oil is one of the most popular single-seed oils among consumers. It is used to season raw vegetables when you want to emphasize natural aroma or to prepare sauces (such as mayonnaise) with a “light” taste. However, like other seed oils, corn oil has a lower commodity value than that extracted from olives.