Wheat meal and flour

The wheat grain consists for 85% of endosperm (flour body), 13% bran (various layers) and 2% germ.

The chemical composition of the wheat grain is:

• 59% carbohydrates (starches and sugars)
• 14% moisture
• 13% protein
• 10% of dietary fiber
• 2% fat
• 2% minerals

Different types of meal and flour can be produced from wheat grains. The criteria for flour is that it can only contain the endosperm; meal also consist of bran parts. Whole meal has a very coarse structure, because it contains the entire husk of the grain, namely the bran. In contrast, Super Patent flour is of a very fine structure, containing only the endosperm. The similarities between the different types of flour is the fact that the germ is always removed. This is due to the fact that the high fat content of the germ speeds up the oxidative spoiling, resulting in a rancid smell and flavor.

The flour quality, and especially the protein content, is determining for its applications. For instance, flour with a low protein content (below 10%) is suitable for use in confectionery products, such as biscuit, and cake. Flour with a protein content of between 10 and 15% is suitable for use in bread. An even higher protein content (higher than 15%) is used in the production of rusk.

The protein content of the flour is determined by the degree of grinding. The core of the grain contains the most proteins; towards the outside of the grain, the protein contents becomes gradually lower. The husk layers virtually do not contain any protein. The higher the degree of milling, the higher the protein content of the meal. The skin layers contain virtually no more protein. So the higher the degree of milling, the higher the protein content of the flour.

Meal and flour production process

Harvesting and threshing

The harvesting of wheat preferably takes place when the grain is sufficiently dry and the grass is properly matured. The harvest takes place during autumn. Threshing can damage the grains, especially when the moisture levels in the grains are low. The combine harvester has to be adjusted properly, ensuring as little grain damage as possible, but with sufficient threshing. Also impurities (like stem and leaf residues) should be avoided. The stems of the wheat plants can be processed into straw.

Storage

First, the grains are stored. This is done in large silos, where dry air is blown through. This dry air is necessary because moisture content of the grain is usually on the high side. By lowering the moisture content below 14%, overheating and deterioration are prevented. Moreover, the brittleness and toughness of the grain can be adjusted, giving it the ideal characteristics for grinding.

Cleaning

There are six purification steps to rid the grains of any impurities.

Sieving

The grains are sieved, removing any coarse contaminants such as paper, sand, straw, husks and twigs.

Magnet

A magnet is used to retrieve any iron particles from the grain. These iron particles are removed in order to guarantee the safety of the final product and to prevent damage to the machines, such as damage to the rollers in the milling process.

Separator (Aspirator)

During the third cleaning step in the separator, also called aspirator, both coarse materials (husks and strands) and fine particles (sand and dust) are removed. The grain is guided over two sieve screens. On top a sieve for coarse materials, and below a small sieve. The grain can fall through the course sieve; the small particles such as sand and dust will fall through the small sieve. What is left over passes through an upward stream of air, any remaining dust particles are sucked away with the air flow, while the grains are collected below.

Destoner

During the fourth cleaning step, stones are removed using a destoner. A vibrating screen (sieve) carries the grains and any stones upwards. A powerful air stream lifts the grains up while the impurities remain on the vibrating screen and are disposed above.

Trieur (Triage)

The fifth cleaning step separates the different types of grains. In a trieur, a rotating drum with indentations in its sides, the cereals are rotated. The indentations are made to exactly catch the grains that have to be collected. Grains that do not fit exactly (being either too big or too small) drop from the slot. The desired grain kernels remain in place longer, and then fall into a collecting tray, which is a stationary part in the middle of the drum. The remaining grains are used for different products, for example, for another meal or flour type, or in the animal feed industry. The trieur is not used if a mix of different types of cereals is purposely made, because then this step would separate the grains again.

Scouring

The final purification step takes place in the scouring machine. Here, the grains are beaten against the coarse side in a drum. Any impurities that were attached to the grain are removed in this way.

Temporary storage

After cleaning, the grains are temporarily stored according to class and protein content.

Conditioning

In order to effectively remove the bran during grinding, the grains are conditioned. The desired moisture content is 16-17%. The cereal grains have a moisture content of 13-16%. In most cases, the cereal grains are thus moistened with 1 to 4% of water. This moistening can be carried out using steam and pressure, and takes up to 8 to 20 hours to complete.

Blending

To obtain the desired grain composition of the meal or flour, some grains are mixed. This mixing process is referred to as blending.

Grinding

After the conditioning step, the grinding process can be started. The grinding process is divided into two phases: the scrap phase and grinding phase.

Scrap phase

During the scrap phase, the conditioned grains are divided into three segments, namely, the germ and bran, large parts of endosperm (middlings/ grouts), and a small amount of fine flour. The distance between the rollers, that are rotating in opposite directions, at different speeds, is reduced after each rolling step. Furthermore, the grooves in the rollers are becoming finer and after every step the whole is sieved.

Brushing

The germs are separated during the scrap phase and the brans are further processed in a bran brushing machine, where any flour particles sticking to these parts are removed. These particles can be ground further down to flour using grinding rollers. The endosperm advances to the final phase: the milling/grinding phase.

Milling/ grinding phase

In this phase the endosperm is first divided into two groups: coarse and fine grinding. The coarse grind (middlings, groat) is finely rolled using up to 12 consecutive smooth rolls. After every rolling step, the whole is sieved, creating different fractions.

The fine grinding, which consists of lumps of endosperm and flour, is cleaned in the middlings purifier. After brushing, the semolina (finest parts) are also milled. The middlings go with the bran to a dissolution roll. Here, the bran is separated from the endosperm.

The wheat grains have now completed a large number of rolling steps. The three streams that ultimately result from the milling process are the bran and the germ, the flour and the meal with small parts of bran and germ. The size of these fractions are dependent on the type of meal or flour. The whitest flour results from the first scrap and milling rolling.

Packing

Before the flour is packaged, it is occasionally bleached some more or enriched with vitamins and minerals during the refining step of the production. In general, the different types of meal and flour are delivered in bulk. In addition, approximately one-fourth is packaged in bulk packs and 5% in small packages.

Food Safety & Hygienic Design

The general rule is, that as long as the product produced is a dry food, each machine design is sufficient, as long as no physical or chemical lubricants are used, and there is no transfer of allergens. This rule applies to the entire production process. From grain to flour, this means a moisture content of 11-16% should be maintained. This rule only applies as long as the machines are only dry-cleaned, and no water is used, and no condensation occurs.

However, the moisture in grain is not evenly distributed. Increased moisture on the outside, can still lead to mold growth, the system must therefore be visually clean. No old product can remain - even though the meal or flour is baked later. There is a high probability that certain fungi will produce heat-stable toxins. Moreover, meal and flour are also used for decoration and are sprinkled on freshly baked bread.

The conditioning step is the critical stage in the production process, due to the use of a relatively large amount of water. This section should therefore be hygienically designed.

For the remaining equipment a GMP design is sufficient, that is, if the equipment is easily accessible and dry cleanable. A thin layer of residual product should not pose a problem, as long as no significant amounts of leftover product stick somewhere in places where condense could be formed.