Lesson 4 - Malting Process
This lesson deals with the malting process. We investigate each stage of the malting process in detail. We describe the required physical and biochemical changes involved in the conversion of barley to malt. We also discuss the vessels used for malting and explain how they help to produce malt of optimum quality.
Steeping Process
Steeping is not simply immersing grain in water. The grain is submerged for set periods and the steeping vessel is left drained for set periods.
Water quality
Water used for steeping should be clean and potable. It must be free of pathogens, dissolved organic material and heavy metals, and should also have low chlorine levels.
Steeping programmes
The appropriate programme for steeping grain varies by variety, season, and time after harvest. Grain changes its ability to malt as it is stored after harvest and can require less steeping and germination after a few months than it would in the first few weeks after the new harvest.
To establish the appropriate programme we need to know:
- Varietal purity (most of the barley must be the same variety)
- Current moisture level
- Germinative energy
- Germinative capacity
- Water sensitivity
- Total nitrogen
The following table shows a range of steeping cycle options and their typical temperature pick-up:
Table: Options for up to three wet and dry stands
|
Steeping Stage |
Temperature (°C) |
Stage Time (h) |
|
1st immersion |
12-15 |
5-10 |
|
1st air rest |
1-16 start; 17-18 finish |
12-14 |
|
2nd immersion |
12-15 |
10-15 |
|
2nd air rest |
15-16 start; 18-20 finish |
10-12 |
|
3rd immersion |
12-15 |
3-5 |
|
3rd air rest |
15-16 start; 19-21 finish |
2-6 |
Let’s discuss some factors to consider when designing a specific steeping programme.
Water sensitive barley
Water sensitive barley can fail to germinate if immersion stands are too long. We need shorter immersions, particularly for the first immersion, followed by longer air rests in order to successfully steep grain with water sensitivity. The total time of a steeping programme for water sensitive barley is longer than one for a normal barley.
Initiation of germination
If we raise the grain moisture to a suitable level to initiate germination (30-33%) and then carry out a long air rest, the grain is able to accept more water without being damaged. If we give too much water too quickly, the grain becomes saturated and is slower to progress to chitting.
Air rest time, temperature and humidity
The duration of the air rest periods is dictated by the volume of air available (i.e. fan size). It is important that the temperature of the grain does not exceed 23°C during an air rest as this can cause damage to the embryo and can impair the enzyme systems needed for germination. Humidified air (> 95% relative humidity) is used to ensure that the grain does not lose moisture.
Key points:
- Each barley variety has an optimum temperature at which it grows, but the typical range for water and air temperatures is between 9-16˚C.
- Grain temperature must not exceed 21-23˚C, to avoid damaging the grain.
- Water sensitive grain should have a short initial immersion, followed by a longer air rest.