The main difference between process flows at feedstuff processing facilities and flour/groats mills is in processing numerous raw materials (over 100) with various processing properties. The materials of plant, animal, microbiological and mineral origin are represented by bulk, coarse, compacted and liquid materials.
The production consists in the sequence of process operations: ingredients reception, shipment, placement and temporary storage, cleaning, grinding, dosing, mixing etc.
Material grinding is an important and energy-consuming operation in the feedstuff production. Accessibility of the feedstuff by animals is directly dependent on the particle size of the ingredients. The quality of feedstuff, regardless of the particle size, is higher if there is less bran (the throughproduct of the sieve with the mesh of 0,2×20 mm). This is due to the fact that the throughproducts interfere with intestinal motility in animals.
As regards raw material fine grinding the most common process is in hammer mills. Single-rotor mills are mainly used. The criterion for assessing the grinding rate is the value called a fineness modulus. The fineness index is determined by the following values of particle size: (2,0 … 1,8) mm – coarse grinding; (1,8 … 1,0) mm – medium; and (1,0 … 0,2) mm – fine. Grinding fineness depends on the species and age of animals and birds, for which the feedstuff is designed.
Glumaceous grain hulling is intended for separating shells from kernels of the oats and barley, used in the production of feedstuff for pigs and poultry. This is caused by the fact that their feed digestive system cannot digest coarse feedstuff with high fibre content. Therefore, oats and barley are ground only after compulsory preliminary separation of shells. Two different techniques are used for hulling. The first one implies that shells are separated with the same machines that are used at groats mills (dehullers with an abrasive cylinder, centrifugal other hullers). The other is as follows: first grain is ground in hammer mills or roll hullers, then the ground product is divided in sieves into three sizes. The first riddling size returns for repeated grinding, the second riddling size moves to the air separator for hull removing and there it joins the throughproduct, which is the ground grain endosperm. The first technique is characterized by relatively high output of the hulled oats and barley grains. The other technique features higher capacity, simplicity and flexibility.
To improve grain quality, destroy starch to the easily accessible rates, neutralize harmful substances and significantly increase the food value of the grain materials, special processing techniques are applied: flattening, roasting, extruding, micronizing etc.
Grain flattening is a relatively new way of grain preparation. It includes hydrothermal treatment with further flattening. The hydrothermal treatment increases the food value of the carbohydrate and protein complexes, saves animal energy for nutrient digestion. While flattening polysaccharides are split, starch changes its structure and is more easily fermented. Generally, this treatment improves the use of the feedstuff, that means ensures its fast and full digestion.
Roasting enhances the grain taste features. The process consists of grain humidifying, heating and roasting at 100…110ºС over 10…12 min with further fast cooling. However, roasting notably lowers protein digestion and accessibility of amino acids. Therefore, roasted grain is limited in the animal diet.
Grain micronizing is its treatment with infrared rays, which penetrate into highly humidified grains and cause swelling. The grain becomes soft and cracks. Grain carbohydrates and proteins undergo structural changes, similarly to hydrothermal treatment. Starch turns into dextrins, which are more easily digested by animals, especially youngsters.
Extruding means that in an extruder the ground grain is heated up to 120…150ºС under high pressure and friction and turns into the powder. Coming out of the extruder, due to the high pressure drop, it swells. As a result of the treatment grain starch turns into dextrins, which are more easily digested by animals. Major part of the microbial flora (bacteria, fungi) is destroyed.
