Maize Milling

THE ORIGIN, CULTIVATION & TYPES OF MAIZE

It is known that maize was cultivated systematically by the American Indians, from Chile to Virginia, from Brazil to California, several centuries before the Maya Civilisation. This preceded the Aztec Civilisation which flourished around 500 A.D. By virtue of its ease of cultivation and the brevity of its vegetative cycle, the plant was cultivated by women whilst the menfolk fought and hunted. In 1492 Columbus discovered cultivated maize in Haiti, where it was known as MAHIZ, a name perhaps originating from the Maya people responsible for its diffusion.

The Indians made a type of bread from maize, baked in an oven and eaten with fish, grasses and vegetables. In addition, using fermented maize, these people produced a type of beer called 'Chicha'.

Maize was introduced into Spain by Columbus, but the first attempts at cultivation only took place some 40 years later.

During a period in Europe when the cultivation of maize was unknown among the majority of agriculturalists, apart from students and botanists, the Portuguese introduced its use to Guinea and the Congo, from where it has become the staple grain crop for much of Sub Saharan Africa.

In Europe, towards 1550, its cultivation spread from Spain to France and Italy and towards the end of the same century, Venetian merchants introduced it to the neighbouring Balkan States, to Turkey and to Egypt. About the same time it was also introduced into China.

Maize Cultivation

Maize thrives best in a warm climate and is now grown in most of the countries that have suitable climatic conditions. Its growth depends more on high summer temperatures than on a high mean temperature. It will ripen in a short hot summer and will withstand extreme heat. A large amount of water is needed during the growth of the maize. Its average maturing period is relatively short and this makes it possible to grow at fairly high latitudes.

In the United States of America, the maize growing area stretches from approximately 40 degrees South to 45 degrees North. In Europe, maize growing reaches as far North as 46 degrees on the West coast of France. From this point, the line runs across Europe reaching 50 degrees in the East before falling, only to rise again in Southern Russia approaching 52 degrees.

The U.S.A. has the highest output of maize amongst the countries involved in maize growing. In 1964 it produced more than half of the total world maize growth, accounting for 104 million tons grown by the nation. Today the world harvests almost as much maize as wheat.

Maize is exceptional in yield per unit area. The harvest may vary from 2.5 to 6 tons per acre according to the soil and its cultivation. Yields above 7 tons per acre have often been recorded.

Types of Maize:

There are about 50 different species of maize having their own characteristic features and kernel sizes, all belonging to a small number of types. Colour and structure, as well as the shape of the kernel, differ from one species to another.

White, Red and Yellow are the most common basic colours of maize, but it is possible to find a wide range of shades, from Red-Brown to Light Red and from a Pale Yellow to Orange.

The shape of the kernel can be divided into two main groups:

The most well known and widely grown varieties are:

In general, the flint glassy-kernel varieties yield better grits than the softer mealy dent maize. Some products, however, require a raw material of the soft type. For milling purposes the maize should be dry and bright. Dull colour often indicates that the maize is old or has been harvested or stored under unfavourable conditions. The germ must be free of mould.

Great importance is attached to the use of sound and fresh grain to give high quality in finished products. The quality of the maize affects the yield and fat content of the grits or flour much more than in wheat milling. Different types and qualities of maize undergoing identical grinding operations will produce grits or flours which vary considerably.

Maize is also known as Corn (U.S.A.) and Mealies (South Africa)

Typical Composition:

The germ has a fat content of up to 30 - 35%

Generally, white maize is used for human consumption, and yellow maize is used for corn flakes, animal feeds and industrial products, eg. starches etc.

Typical Analysis:

Bulk Density:

45 lbs/cu.ft.
70 kg/hl
56 lbs/bushel

The age of maize is significant because the fat migrates from the germ to the endosperm during storage. This fat migration is more pronounced during unfavourable storage conditions, ie. in the open directly exposed to sunlight, or contained in unsuitable bins or buildings constructed or corrugated iron sheeting.

Storage periods up to 6 months have been found to cause little fat migration. After 18 months, however, the endosperm may contain up to 3 or 4 times more fat than it did initially. Fat content and distribution may vary considerably, as shown by the following laboratory analysis of maize kernels:

It is evident therefore that in raw maize, the endosperm may have an extremely high fat content (in excess of 1%). In such a case, it is impossible to produce a finished product such as grits with less than 1% fat by industrial methods. It is advisable to pay attention to oil (fat) content of the endosperm when purchasing maize for milling.

The quality of maize is very variable and influences the milling system.

Maize grown in European countries is often harvested at over 25% moisture content and requires drying to below 14% for storage.

Naturally dried maize will give superior milling results to maize dried artificially. The minimum fat content and the extraction of grits of a given fat content are significantly affected.