The features of grain raw material grinding
Advanced Grain Grinding Technologies
The preparation of grain mash is one of the key stages in alcohol production. Preparation of starch-containing raw materials includes grinding, mixing with water, preheating, hydrothermal treatment, and saccharification. The mechanical properties of grain largely depend on its moisture content. Dry grain is brittle, while wet grain is more plastic. This is caused by changes in the colloidal properties of starch and proteins. The specific energy of grain increases as its moisture content rises. These properties are considered when processing grain into alcohol and selecting grinding equipment. Mechanical and chemical breakdown changes material properties, reduces molecular weight, changes solubility, and accelerates chemical reactions. It also increases the biochemical activity of the raw material.
Grain Grinding Technologies
Mechanical dispersion changes the size and shape of raw material particles. Increasing the particle surface area significantly accelerates technological processes. Highly dispersed grain mash does not require pressure cooking and improves raw material utilisation. The grinding degree is characterised by particle size, with 60–90% measuring between 0.25 and 1 mm. Excessively fine particles undergo intensive thermal treatment and form oxymethylfurfural and melanoidins. Large starch particles dissolve incompletely, increasing losses of fermentable substances. Many plants use a two-stage grinding process to achieve finer and more uniform particle size. First, the grain is ground in a hammer mill and separated into fractions by particle size. The coarse fraction is then reground in roller mills to improve grinding efficiency.
High-Dispersion Grain Mash
The use of a two-stage grain grinding method reduces the temperature and boiling time of the raw material and reduces losses of fermentable substances. However, using this method complicates the technological scheme, requires additional equipment and production areas, and increases the energy consumption for grain grinding and transport of the ground material. The disruption of the cellular structure of the raw material is achieved by grinding it in crushers and special machines, followed by mass thermal treatment with water. Highly dispersed grain mashes obtained using disintegrators, ball mills, corundum, jet, and other machines not only have a disrupted grain structure, cells, and starch grains but also mechanically disrupted polymers (starch, proteins, etc.), allowing them to be thermally treated with water at temperatures not exceeding 100°C. The use of highly dispersed grain mashes reduces losses of fermentable substances during thermofermentative treatment and decreases the consumption of thermal energy.
Mechanical-Chemical Activation of Grain
Promising for the alcohol industry is the development of advanced alcohol production technologies using disintegrators, vibratory devices, electromagnetic and other grinding devices to more efficiently use raw materials and saccharifying materials. Grain crops are ground by mechanical means using hammer mills of various designs or roller mills. The most common hammer mills are types DM, DDM, A1-DDM, or roller mills of type ZM. Disintegrators and dismembrators belong to impact-type grinders. They are used to obtain highly dispersed mashes. An important property of disintegrants is that the processed material undergoes mechanical activation. The activation of substances under the influence of high mechanical energy is a new progressive way to improve technological processes. This phenomenon is called mechanical-chemical activation (MCA) of raw materials and intermediate products in alcohol production.
Hammer mill of DDM type
Drum of a hammer mill
Importance of Grain Grinding Quality
In the preparation of grain mixtures with a high degree of grain grinding and the use of hot water, flour lumps can form. This most often occurs when preparing a mash with a high dry matter content with a hydraulic module of 1: 2.5…1: 3.0. The formation of lumps deteriorates the conditions for the thermofermentative treatment of raw materials, increases the loss of starch. During the stage of enzymatic hydrolysis, the access of enzymes to the biopolymers of raw materials is hindered, fermentation slows down, and the acidity of the mash increases.
As mentioned above, one of the main indicators of the initial stage of the technology is the degree of grain grinding. The finer and more uniform the grind, the lower the costs for its further processing. In particular, the degree of grain grinding affects such technology parameters as the “grain: water” ratio (the so-called hydro-modulus) when preparing grain mixtures, the temperature, and the duration of thermofermentative treatment.
According to current regulations, grain grinding quality is determined by separation on 1.0 mm sieves. However, grind uniformity, which is essential for hydrothermal treatment, is not considered. The grind contains fractions with particles differing in size by 10 to 100 times. Each fraction requires a specific hydrothermal regime to minimise technological losses. In practice, achieving optimal conditions for all fractions is difficult. High temperatures cause sugar caramelisation in fine particles. Lower temperatures result in incomplete starch dissolution in coarse particles. Reducing losses and energy consumption requires highly dispersed and uniform grinding. Uniform grinding also helps reduce mash hydro-modulus and improve alcohol production efficiency.
Grain dismembrator
Hydro-Modulus and Mash Viscosity
Reducing the hydro-modulus of the mash allows for simultaneously reducing the output of stillage and cutting down on technological costs for heating, cooling, transferring semi-finished products, and distilling mature mash. However, when reducing the hydro-modulus of the mash, due to increased concentrations and starch gelatinisation, there is an increase in its viscosity, leading to decreased flowability, especially at temperatures of 70…80°C. In fact, this is a limiting factor in implementing the grain processing technology under conditions of elevated concentrations. To reduce the viscosity of highly dispersed mashes with increased dry matter concentrations, it is necessary to use thinning enzyme preparations.
High fluidity of semi-finished products is important for reducing the load on mixing and pumping devices, as well as for the efficient execution of heating and cooling processes, preventing sediment formation, and so on.
