Supply / Cleaning
First, supplied maize has to pass the incoming inspection. If it meets with the specifications of the respective starch factory, it is coarsely sieved to separate contaminations, e.g. stones, cobs, dust particles, foreign grain material, and fine material. After cleaning, the maize kernels are stored and then conveyed into steeping tanks.

Steeping
Well-conducted steeping is an important prerequisite for high yield and good starch quality. At first the purified maize kernels are transferred into a tank containing steep water. This step is conducted at 50 °C and lasts about 40 to 50 hours. Steeping tanks are commonly series-connected and operated by the counter flow principle. For optimal steeping conditions steep-water is kept at pH 4 by addition of sulphuric acid or hydrochloric acid and treated with sulphur dioxide. These conditions guarantee optimal water absorption of the maize kernel, controlled fermentation by lactic acid bacteria and loosening of the protein matrix. At the same time steep water causes the softening of the kernels and the release of solubles. Growth of lactic acid bacteria suppresses unwanted microorganisms such as yeasts, molds and other bacteria. During steeping the size of kernels nearly doubles and the water content increases from 15 % up to 45 %.

Coarse grinding and degermination
After steeping one is able to mash the maize kernels with a finger nail and remove the skin easily. After this processing step it is also possible to take the germ out of the broken maize kernel. This effect is utilised during the so-called degermination step.

To free the germs the kernels are coarsely ground in an attrition mill. The grinding has to be conducted with care to avoid oil leakage out of the germs. Otherwise the oil is soaked up by the starch granules, which leads to reduced starch quality. Separation of specifically lighter germs is conducted by means of special hydro-cyclones. For complete degermination the grinding and degermination steps are performed twice. Afterwards the germs are washed and dried and finally sold to companies which utilise them for corn oil production.

Fine grinding and extraction
The germ removal step is followed by fine grinding in an impact mill to completely disrupt the cells of the endosperm and release the starch granules. The resulting suspension is led over bend green cascades for separation from fibre and other maize components. The starch milk, which contains the protein fraction, the so-called gluten, passes through. The bend screen cascades are connected in series. For complete washing out of the starch and separation of the fibres they are operated by counter flow principle. Additionally, washing water is added to the last process stage.

The separated residues are dehydrated and dried for use as an animal feed component referred to as maize feed.

Gluten separation
The crude starch milk still contains all the dissolved proteins. This fraction is called gluten, and most of it is separated off by means of two successive nozzle type continuous centrifugal separators. The process utilises density differences between starch and protein. The protein fraction is dehydrated by means of a rotary drum filter, then dried and used as a high protein feed additive. It is mostly given to chicken, since its high xantophyll shares positively affect egg yolk pigmentation.

Starch refining
The starch milk, which still contains approximately 2 % of protein and fibres after separation, is then refined in a multi-step cyclone plant. The last stage of the multi-step cyclone plant is the one and only step of the wet milling process where fresh water is added.

By optimal construction and adjustment of the plant it is possible to reduce the protein content in the starch below 0.3 % on dry matter. Hydro-cyclone plants have become accepted for starch refining for their high performance, their low water consumption, and their low maintenance efforts.

Dehydration and drying
The refined starch milk, having a water content of approximately 65 %, is dehydrated in peeler centrifuges to a residual water content of about 40 %. The inner layer of the filter cake is coloured yellow and contains high amounts of protein. It is reintroduced into the process. Pure starch is finally dried by means of a flash dryer. For optimal shelf life residual moisture must not exceed 14 %.