Maize milling involves the processing of maize in order for it to be safe for consumption. And at Zesto’s mill, this is exactly what we do every day. The process starts off with the cleaning of the grain and the conditioning of the maize which is done by damping the maize with water and allowing it to sit for a specific amount of time.
Cleaning and Conditioning Process
The cleaning of maize is one of the most important steps in the entire process. During this process, foreign materials and all but the maize kernel is removed from the grain that is to be milled. These foreign materials, as well as the husk, dust, sand and straw, lowers the quality of the kernel. This process also involves the removal of any poisonous seeds and materials which might be harmful to the milling equipment.
The conditioning of the maize involves moisture being added to the maize which will allow the bran to be easily peeled off during the milling. This also allows for easy separation in the sifter and it will add mass to the meal.
Once the maize has been cleaned and conditioned, the milling can take place in any one of the following ways.
The lowest cost option and one that is representative of an undefined class is the hammer milled maize. This method is generally used in rural situations. As a result, the meal that is produced is generally considered to be lower quality because the germ, the bran and the endosperm are ground up together which results in a meal that:
• Has a shorter shelf life as the germ becomes rancid very quickly.
• It has a lot of powder which results in the high absorption of moisture which can turn porridge sour when cooked.
• The porridge will have a yellow colour.
• It can lead to the feeling of being bloated when eaten.
The other process is done through the use of a hippo hammer mill, the maize can be de-germinated prior to milling and this results in a better quality sifted meal.
Finally, for a better quality meal, the maize is de-germinated at either 3 tons per hour, 1.5 tonnes per hour or at 500kg per hour. Then the samp and chips will be milled using a plate mill or a hammer miller. The meal needs to be sifted through a plate or roller but is not required if the meal is sifted through a hammer mill.
Best quality maize, sifters and maize mills
To get the best quality maize, the following needs to be done:
Maize needs to be de-germinated prior to the milling and the milling needs to be done with rollers instead of a hammer mill or a plate mill. Should the budget be tight, maize can be milled using a plate mill and then sifted. As a result, a large part of the bran and the germ should be sifted off. This will result in special sifted meal, which can be lower quality.
Along with milling, sifting is the essence of maize processing.
The sifters, ideally, should be one of the following:
Turbo Sifters: These are two horizontal shafted separators with steel screens. They have a high capacity but are not able to sift finely. These are generally used in smaller plate mills and as graders for samp and for primary grading after de-germinators.
Rotary Sifters: These are three horizontally shafted separators with nylon screens. They have a lower capacity and are capable of fine screening. These are used in smaller plate mill systems.
Mini Plan Sifters: These sifters have a higher capacity and are capable of fine screening and as a result are often used as primary sifters for all kinds of mills, including those sifting 1 ton or 2.5 tons per hour.
Plan Sifters: These come in various sizes and have a very high capacity and are able to handle fine screening. They are used in mills with a capacity of 2.5 tons per hour or more.
When looking at an industrial mill, you are likely to see that they are constructed over one or more levels. Your high capacity mills will usually require more levels and will use gravity to move the product between the mills and the sifters.
For smaller mills, it might be ideal to place them in containers. This is done for special applications where the buildings might be a bit problematic or where the mill might need to be moved occasionally. This is ideal for mills that are using temporary power or are situated in a remote location.