Lesson 5 - Malting Process SAQ

SAQ:

**What aspects of grain biology and the steeping process affect the rate of water uptake? What can maltsters do to ensure effective hydration of the grain during steeping?

Response:

The purpose of steeping is to increase the grain moisture from around 12% to between 43-46%. This increase must be even across the grain.

Grain water uptake is influenced by several factors. These include:

Temperature

Water uptake is faster at higher temperatures. After six hours of steeping, there is not a lot of difference between the water uptake at 10°C and that at 20°C. So, all barley in this temperature range will increase in moisture content from 12% to 25%. However, after a further 14 hours of steeping, the moisture levels will increase to about 36% at 20°C but only to around 30% at 10°C. We must bear in mind that although warmer temperatures during steeping can lead to faster hydration, they can cause uneven hydration and hence modification so we need to find a balance.

Grain size

Smaller grains reach the target moisture content faster than larger grains. This is simply because there is less material to hydrate, and shorter distances for the water to move through in the grain. That said, smaller grains tend to be higher in protein so smaller size is not necessarily a guarantee the grain will hydrate rapidly. The most even water uptake and overall hydration is found in grains in the size range of 2.5-2.8 mm.

Protein content

High protein grains typically have less free space through which water can move. As a result they hydrate more slowly than low protein grains. 

Grain viability/water sensitivity

Dead and dormant grains take up water very slowly after an initial increase in moisture because they don’t germinate. If the maltster is trying to malt dormant or dead grain, the uptake of water is incidental because they will fail to malt in any case! Water sensitive grain requires more extensive air rests to ensure it hydrates and this can lead to a longer total hydration time.

Barley growing conditions

Growing conditions affect the grain’s water uptake. Rain during a specific stage of ear-filling can lead to the husk splitting, leading to faster water uptake.

Air rests

Grains hydrate more evenly when air rests are incorporated into the programme as more water enters the endosperm during the rests.

To enable effective hydration, the maltster needs to ensure the grain has the ability to germinate before committing to steep it. Grains with homogeneous size must be used so grains should be screened to ensure they are in the size range of 2.5-2.8 mm. If the grain shows water sensitivity a modified steeping regime with shorter immersions, particularly for the first immersion, followed by longer air rests is required. The total time of a steeping programme for water sensitive barley should be longer than for a normal barley.

Controlling temperature is also important. Steep water temperature should be at 12-15°C and air rest temperature should be increased with each rest from 17-18°C at the end of the first rest to 19-21°C at the end of the last rest. This should achieve the balance between speed of hydration and evenness of modification. Maintaining moisture levels by humidifying the air supplied during air rests is also necessary. Washing barley before steeping also helps reduce the amount of time the grain needs to be steeped by starting the hydration process.