Corn is one of the most cultivated cereals in the world, alongside wheat and rice. However, unlike wheat and rice, its consumption in the form of flour is much less common. The reason for this difference lies in the large amount of corn used for animal feed and industrial production of starch and derived products, some of which are returned to the food industry. There is also a significant amount of corn used for biofuel production.

Although food products containing corn are diverse, in western countries, the majority of corn for human consumption is used in the production of snacks and breakfast cereals. These industries require grits and large corn pieces rather than flour. There are some specialized semolina companies that work with corn. These companies use either domestic or imported grains, but it’s crucial for them that the grains are hard so that they do not break into small particles (flour), which are undesirable for their main customers. However, corn grains have both hard and softer parts, so some particles generated in the milling process have the particle size of flour. This is the origin of most corn flours marketed in western countries.

The corn milling process begins with grain cleaning and a friction operation to remove the germ and bran. Once these parts are removed, the endosperm (central part of the grain) is milled with roller mills gradually until the desired particle size is reached. The finer fractions generated are separated and sold as flour, but the majority of the production consists of semolina and grits (large grain pieces). The germ can be used to obtain oil, but in western countries, it is more common for it to be mixed with bran and sold for animal feed.

In general, snack and breakfast cereal industries prefer coarse semolina, so the finer semolina (thicker than flour but thinner than coarse semolina) is usually sold to the brewing industry, which uses it as adjuncts. These adjuncts are sources of fermentable carbohydrates that do not impart identifiable flavours in beer, unlike malt, and are very common in most beers. Thus, the brewing industry has become one of the main customers of corn semolina mills.

It should be noted that the use of corn flour in western countries is very minor, and there is no specific industry dedicated to corn flour production. On the contrary, corn flours present in the market are more of a need to commercialize a byproduct and, therefore, are less carefully managed than main products.

Corn is a very diverse cereal, and there are varieties adapted to different uses, such as varieties intended for popcorn production, which have a high expansion capacity. There are also soft varieties, more suitable for flour production, but in western countries, as we have explained, hard varieties are preferred due to the higher consumption of coarse semolina. Similarly, although most people associate corn with a yellow or orange colour, there are corn varieties of different colours, ranging from white to purple or even black. White corn varieties produce flours with colours more similar to wheat and less intense flavours, so they have been incorporated into western countries semolina industries in recent years, partly due to the growing demand for gluten-free products more similar to wheat originals. In other countries, the consumption of these white flours is very common traditionally, such as in Venezuela, where arepas and other products derived from these flours are part of the basis of their diet. In recent years, there has also been growing interest in the use of products generated from purple or darker-coloured varieties due to their higher presence of antioxidant substances and polyphenols, and therefore better nutritional characteristics. The offer of this type of flour in western countries is very limited, and if incorporated into any formulation, organoleptic aspects must be taken into account.

Applications of Corn Flours

In western countries, the most common use of corn flour is to mix it with wheat flour in small percentages to make what are called corn bread, which are actually bread enriched with corn, in most cases. Traditionally, there has been a lot of trickery with these issues, but the new Technical Sanitary Regulation of Bread in Spain (July 2019) indicates that only bread made with corn flour alone (without mixing with other flours) can be called corn bread. In the case of bread made with flour mixtures, the name of the cereals used and the percentage of each in the mixture must be specified in the product name. This practice results in bread with a specific personality (colour and flavour), but the baking quality of the mixture is inferior to that of wheat flour, so stronger flours, dough reinforcing improvers, or longer processes must be used. In general, yellow or orange corn flours are preferred as they provide the typical corn characteristics associated with corn in western countries. In these cases, the quality of the corn flour does not significantly influence the final result, beyond its colour and the proper removal of the external parts of the grain.

In some areas of northwestern Spain and Portugal, it is common to use corn flours in bread making for reasons of tradition and culture. In these areas, the incorporation of these flours is common, often produced in small local mills, typically stone mills, in higher percentages. One of the most well-known breads with a high proportion of corn flour is Portuguese broa bread. To make this bread, wheat, rye, and corn flours are usually mixed. In the processing, the flour (whole or in part) is subjected to a scalding process with boiling water. In this operation, the starch gelatinizes, and the consistency of the dough increases. Consequently, yeasts must be added later to prevent them from being inactivated by heating. The bread, usually large in size, has a more yellowish colour, a typical flavour, and a less cohesive texture. In breads where corn flours are incorporated in high percentages, the baking techniques are more similar to those of gluten-free breads than conventional baking, and in these cases, the quality of the flours is more important if homogeneous results are desired.

Another growing use of corn flours in recent years is their incorporation into formulations of gluten-free breads and products. In these cases, although yellow corn flour can be used, I would recommend using white corn as it produces products with a colour more similar to wheat products and with a less pronounced flavour. These corn flours yield excellent results in cookie making, but in cake making, rice flours are usually preferred. The use of these flours as the main ingredient in gluten-free bread making is also not very common, but they are used in small percentages in some preparations. The reason these flours are not widely used is because they do not offer significant advantages over the more commonly used flours, their limited availability in the market, and they tend to be quite irregular, as we will explain below.

Quality of Corn Flours

As we have mentioned, most of the corn flours marketed in western countries are a byproduct of corn semolina production and therefore come from hard varieties. In general, the flours come from the softer parts of the grains, and therefore, they are obtained naturally without the need to damage a large amount of starch. However, if there is a need to produce more flour, it is possible to obtain it from semolina, and therefore from the harder parts of the grain, which requires more energy expenditure and generates more damaged starch. These differences in the amount of damaged starch translate into different water absorption capacities of the flours and differences in their thickening capacity, which can generate differences in the doughs and products made from them.

In addition to the amount of damaged starch, corn flours may differ in their protein content, depending on the variety and the edaphoclimatic conditions to which the plant has been subjected. A higher protein content is associated with a lower starch content, and therefore, changes in its thickening power, both cold and especially after hydrothermal treatment (cooking). While there are differences in protein content, these are usually much less important than those found in other cereals such as wheat since the protein level in corn is usually lower.

Another factor to control is the particle size of the flours. Since they come from hard grains, corn flours are usually coarser than wheat flours. Wheat flours typically have an average particle size close to 100 microns. In general, sieves of 180-200 microns are used to separate what is considered flour, but there can be significant differences below this particle size. In principle, coarser flours are preferred for making cookies, and finer flours are preferred for cakes, but in general, particle size will affect the functionality of the flours in different preparations. It should also be considered that to obtain finer flours, it may be necessary to damage a higher percentage of starch granules, which can also affect that functionality.

Finally, the colour of the grain must be taken into account, but this parameter is usually quite regular in the flours marketed.

In general, to have regular corn flours, the particle size and the content of damaged starch and protein, or their water absorption capacity, must be defined. Differences in corn quality will be important in those products where corn flour is the main ingredient, losing importance in those products where it is added in small proportions. Thus, in gluten-free cookies made with corn flour, flours with more damaged starch or more protein content tend to generate more consistent doughs that expand less in the oven and produce cookies with a smaller diameter and greater hardness. This effect can be corrected by adjusting the moisture content in the formula. Similarly, in breads where flours with a higher content of damaged starch and protein are used, the amount of water must be increased in the formulation.

Special Corn Flours

The first thing that may surprise us is the presence in the market of the so-called fine corn flour. In reality, what is hidden behind this denomination is not fine flour but cornstarch. Therefore, it is a misleading denomination, as it does not equate to the flour of other cereals, existing corn flours, which I believe should be prohibited. Starches will be discussed in another entry.

There is a wide variety of corn flours that have undergone heat treatment. Among these, pre-cooked flours stand out, very typical in South American countries, used to make products such as arepas. There are also so-called instant flours, which have undergone heat treatment to gelatinize the starch and thicken batters with water without the need for heating. These flours are used, for example, to make polenta, a product widely consumed in northern Italy. The particularities of thermally treated flours depend on the temperature to which the starch has been subjected and the humidity it possesses during heating and are dealt with in a section dedicated to this issue.

In the case of corn, and unlike other grains, there are flours from grains that have undergone a process of alkaline cooking, known as nixtamalization. In this process, the grain is cooked in a mixture of water with lime to soften the external parts and remove them easily. After this process, the wet grain is ground to form a paste used to make a variety of products, such as tortillas, snacks, nachos, fried strips, etc. This paste can be dried and ground to obtain flour from which these products are generated. Nixtamalization is a process used since ancient times in the American continent and, in addition to facilitating the removal of the external parts of the grain, gives the products a special flavour.

As in other cereals, there are corn varieties whose starch does not contain amylose and therefore is composed only of amylopectin. These are the varieties known as waxy. The gels obtained with these starches do not tend to retrograde and present very different characteristics from those obtained with normal varieties. There are also varieties with a high content of amylose and a lower content of amylopectin, and therefore with a high tendency to retrograde. However, these varieties are mostly used by the starch industry, and there is hardly any supply of flours from these varieties.

Finally, it should be noted that, although very little known, it is possible to obtain whole corn flours. In the milling process, the external parts of the grain are separated. The germ has a high oil content, so if it is incorporated into the flours, it tends to become rancid very quickly. The corn bran is much harder than that of other cereals, so it has a hard texture, even after milling. To solve both problems, it is possible to resort to cooking (hydrothermal treatment) of these parts of the grain before incorporating them into the flour from the endosperm. It is also possible to obtain wholemeal flour directly and treat the entire flour thermally to inactivate the enzymes that enhance rancidity and soften the bran. But in this case, the process must be very well controlled to avoid gelatinizing the starch, something that would significantly change the properties of the flours, increasing their thickening power in cold, and reducing it in heat.

Nutritional Aspects

In general, corn flours do not have better nutritional quality than wheat flours since they have a higher starch content and lower protein and fibre content. It is true that corn contains a higher number of carotenes, colouring substances that provide the typical yellow colour to flours, with interesting nutritional characteristics. Obviously, white varieties have a lower content of these pigments. On the other hand, purple varieties have a higher content of anthocyanins. Both carotenes and anthocyanins increase the antioxidant capacity of the generated products. However, the minority use of these flours in preparations means that the contribution of these substances is very low, and there are no studies demonstrating nutritional advantages in the intake of these products with these levels of corn flour.

As in all cereals, whole corn flours are much more interesting nutritionally than flours made from only the endosperm of the grain. Wholemeal flours contain a higher amount of fibre, mainly arabinoxylans, as well as more vitamins, minerals, and antioxidant substances. However, the use of these flours is very minor.

More information:

Serna-Saldivar, S.R.O. (2018) Corn: Chemistry and Technology. AACCI. St Paul, MN (USA)