During steeping, water slowly penetrates the inside of the grain, while soluble nutrients move from the embryo-adjacent part to the embryo. Some components (proteins, starch, cellulose) swell, and the volume of the grains increases by approximately half. The color of the grains changes from straw-colored to brown. Bitter substances, tannins, polyphenols, colorants and other compounds that hinder water absorption are removed from the husk. Toward the end of this stage, rootlets begin to grow outward from the grain. If this phenomenon, known as eyeing, occurs throughout the entire batch, the grains are evenly steeped.
Barley is usually steeped until it reaches 42-48 percent water content. The degree of steeping of the grain transferred for germination depends, among other things, on the type of malt being produced (e.g. in the case of Munich malt, the degree of steeping should be 1-2 percent higher than in the case of Pilsner malt) and the properties of the barley (e.g. sensitivity to water, protein content, etc.). All grains should be provided with identical water absorption conditions that are as close as possible to natural conditions. The increase in enzymatic activity associated with the beginning of growth processes can already be observed when the water content of the grain reaches 30 percent and there is optimal air access.
The following factors affect the rate of water absorption:
Steeping time. The highest rate of water absorption is observed during the first period of grain steeping. This rate decreases over time due to the equalization of osmotic pressure and tension in the semipermeable cell membranes.
Water temperature. The higher the water temperature, the shorter the time required for its absorption. However, steeping grains in high-temperature water carries the risk of fungi and mold development. It is generally accepted that the optimal water temperature is 15-20 degrees Celsius. The rate of water absorption does not depend significantly on the content of dissolved mineral salts or active acidity. However, using water that is too hard and contains a lot of iron is unfavorable.
Amount of oxygen. Oxygen uptake is directly proportional to water absorption. The more water the grain absorbs, the more intensively metabolic processes take place and the higher the oxygen consumption. Oxygen deficiency leads to intramolecular respiration and, consequently, to the formation of undesirable chemical compounds, such as acids, alcohols, esters, etc., which negatively affect the aroma of the malt.
Protein content. Grains with a higher protein content (so-called glassy grains) are characterized by a lower rate of water absorption.
Grain thickness. Slender, mealy grains (with a high starch content), as well as damaged grains, absorb water more quickly and are highly susceptible to the development of microorganisms.
Degree of grain damage. Due to the higher rate of water absorption in grains with damaged husks, the sprout (cotyledon) grows too quickly at the site of the damage (such grains are called hussars). This is an undesirable phenomenon because malt obtained from such raw material has lower technological value.
There are many methods of steeping barley, but currently three solutions are used mainly: air-water steeping, steeping with a constant flow of aerated water, and spray steeping. The choice of the appropriate method should be preceded by an analysis of its effectiveness, taking into account the criteria of the degree of steeping, steeping time and water consumption.
Air-water steeping involves alternately keeping the grains under water and without water. The water is usually changed 2 or 3 times a day, and the grains are alternately kept under water for 3 hours and without water for 6 hours. During air steeping, the rate of water absorption by the grains is higher than when the grains remain under water continuously. When the grains are immersed in water, intensive aeration should be carried out. This is the best way to properly oxygenate the grains. It is also very important to simultaneously remove the carbon dioxide produced as a result of metabolic processes taking place in the grains.
Steeping with a constant flow of aerated water enables the continuous removal of carbon dioxide, impurities and substances leached from the husk. Unfortunately, it involves significant water consumption.
Spray steeping is used after the grains have been thoroughly washed and pre-steeped using the air-water method. In the final phase of steeping, the grains are sprayed with water while carbon dioxide and substances leached from the husk are continuously removed.
Depending on the method selected and the conditions under which the steeping process is carried out, the time required to achieve a degree of steeping of 42 to 48 percent may range from 36 to 72 hours, while water consumption may amount to 5 to 14 cubic meters per ton.
To obtain a homogeneous product, in which the grains have a similar water content at the end of the steeping stage, barley of a single variety that has been properly cleaned and sorted should be used. Maintaining appropriate hygiene in the rooms and equipment is also important. This helps reduce the risk of undesirable microorganisms developing. In addition, the degree of grain steeping should be checked periodically.