Soaking in beer production
Malt Steeping – First Step of the Malting Process
The malting process mimics much of what happens in the field as a new crop of barley grows from seed. It is a three step process comprising ‘Steeping’, ‘Germination’ and finally ‘Kilning’ (drying ) of the grain. Malting first starts by drying barley grains to moisture content of around 12-14%, and then storing for around six weeks to overcome seed dormancy. When ready, the grain is immersed or ‘steeped’ in water two or three times over two or three days to allow the grain to absorb moisture and to start to sprout. The barley moisture is raised from 12% to about 42-46%.
Steeping can be undertaken in a number of different ways:
- Water and Air Steeping
This is based on a succession of wet and dry phases where grain is submerged in water for a few hours then allowed to "breathe" after the water is drained away. Typically water is changed 2-3 times per day for a total of 2-3 days and the process involves steeping with water for 3-6 hours followed by 6-9 hours without water. The aeration provides the barley grain with oxygen and avoids grain suffocation. Customer specifications, water temperature, barley variety, protein level and the age or condition of the barley will determine the length of time required for each stage of immersion and aeration. Water adsorption is greater using this method than by permanently keeping the grains submerged in water.
- Constant Flow of Aerated Water
This allows for the permanent removal of carbon dioxide and any substances extracted from husk. However a disadvantage of this process is the high water consumption.
- Spray Steeping
This is applied after grains have first been washed and then undergone a preliminary "water and air steeping" phase. Grains are sprayed with water allowing permanent removal of carbon dioxide and any compounds that may have leached out. Spray Steeping is carried out in specialised vessels and an obvious advantage of this method is reduced water consumption and significantly reduced effluent production. At the end of steeping, the root (chit) begins to emerge from the grain, showing as a white dot. When the grain has reached the desired moisture content, it is transferred to the malting or germination floor, where it is constantly turned over for around five days while it is air-dried. The grain at this point is called "green malt". The green malt is then kiln-dried to the desired colour and specification. Malts range in colour from very pale through crystal and amber to chocolate or black malts.
- Initial moisture content of barley: 12-14%
- Final moisture content: 42-46%
- Time scale for steeping: 2-3 days
- Steep water temp: 5°C-18°C (41°-64°F) depends on the particular practice of individual plant
(The warmer the water the faster the water is absorbed. However, if the temperature is too high this can result in reduced availability of oxygen and increased growth of micro-organisms)
- pH of first Steep Water: pH 9-9.5
(Some maltsters add sodium hydroxide to lime to fist steep water in order to raise the pH to around 9.5. The alkaline conditions assist in removing any detrimental substance from the husk)
- pH of remaining Steep Water: neutral
How Much Water Is Used In Malting?
On average for every tonne of malt produced 4.5–5.0 m3 water is required for the steeping process and the wastewater generated is approximately two thirds of this1 Annual data for EU maltsters (2006)1:
- 44 million m3 water
- 30 million m3 wastewater
Cost varies depending on how water is sourced and wastewater treated. Using average costs water sourcing and treatment approach € 100 million per annum
- EUREKA SWAN - Reduction of water use in the EU Malting Industry (AR0916); Link: randd.defra.gov.uk/Document.aspx?Document=AR0916_7353_FRP.pdf