Grain milling is the process through which cereal grains such as corn, oats, rice, wheat, etc., are ground to produce flour. There are various reasons why grains are milled, but mostly it reduces cooking time, improves palatability, or produces other food products.
Agricultural processing of grains involves a set of activities carried out to conserve the agricultural produce to make it more usable as food and produce other useful by-products. It is important to note that different grains have unique processing methods depending on the desired products.
There are several distinct steps involved in grain processing. They include:
Grains get contaminated either in the growing fields or during harvesting and storing. Thus grain millers should adequately clean grains before milling to remove the contaminants since they are likely to affect the final product’s quality and pose significant threats to human health. Traditionally grains were cleaned by washing, winnowing, sorting, and sifting. However, with increased grain production levels and developments in technology, equipment such as blowers and air fans are increasingly being used to increase efficiency. Cleaning removes extraneous matter such as straw, chaff, weed seeds, soil, and rock particles and also unfilled or substandard grains.
It is the classification of grains based on their commercial value, quality, and set standards. It is done to prevent further processing of spoilt or blemished seeds that do not meet the official quality requirements. Grading can be done by hand, although it can be cumbersome and time-consuming. Machinery can be used when the physical characteristics are not indicative of the quality of the product. Grading of grains is done by testing smaller quantities sampled randomly and tested in a laboratory using specified equipment to ensure quality consistency.
Unlike traditional methods where grains were milled using two stones, modern roller mills have been manufactured to make milling effective and efficient. In the roller mill, the seed components such as the outer layer (bran), the germ, and endosperm are separated. Various fragments of the grains are then sorted based on the sizes or weight and passed through a series of sieves and other machines to isolate the components.
Modern milling machines allow the millers to remove the bran and grind the endosperm into flour and sift the ground particles to remove ground flour at every stage. Typically most mills have up to four brake rollers and a series of reduction rolls. Some grain particles pass through one roll, while others may have to pass through multiple rolls before they are sufficiently ground.
After the milling process, the flours are appropriately blended to meet the specifications of customers. Wholemeal flours are produced when the bran, germ, and flour are blended back together. Increasing attention is nowadays being given to wholemeal flours due to their high fiber content.
Proper packaging is critical after the milling process since it determines the shelf life of the flour. Satisfactory packaging should be done using appropriate packaging material because flours are more prone to biological and physical deterioration than grains. The packaging material should ensure the right humidity since flour quickly develops molds when exposed to an equilibrium relative humidity above 70%. Additionally, the ideal packaging should protect spillage of the contents, have good insect resistance properties, and have the strength to withstand storage and transportation hazards, among other qualities.
Like any manufacturing process, grains’ processing produces several by-products such as bran, which can be used as poultry or cattle feed. Other products such as oils for various uses are manufactured using the germ of different grains. Thus, grain millers need to use or market the by-products for agricultural sustainability adequately.