Malting
Steeping, germinating, and drying grain to produce malt for brewing.
Malting turns grain into malt through three steps: steeping, germinating, and drying. During germination, enzymes develop that convert starches into sugars like maltose, maltotriose, and maltodextrines. The malt producer halts germination once the enzyme levels are optimal. Most malt goes to brewing or whisky production, though it can also become malt vinegar or malt extract. Barley is the most common grain used, but sorghum, wheat, and rye are also malted.
Traditional floor malting spreads grain in a thin layer on a solid floor, where workers rake and turn it by hand to keep it loose and aerated. Modern malt houses automate the process: grain germinates on a slotted floor that forces air through the bed, and large mechanical turners—such as Saladin boxes—handle much thicker beds, boosting productivity and energy efficiency.
At the malt house, grain arrives from the farmer and is cleaned, dressed, and dried if needed to preserve its quality. It undergoes tests for moisture content, nitrogen content, foreign matter, fungal growth and metabolites, germinative capacity and energy, and water sensitivity. These checks ensure only suitable grain enters the process.
Barley with more than 13% moisture must be dried before storage, or it loses germinative capacity. Heated air (up to 50 °C) circulates through the grain in dedicated driers or a kiln. Over-drying or high temperatures damage or kill embryos, preventing germination after steeping. Properly dried barley can be stored safely for up to 18 months without fungal growth or loss of vigour.
Cleaning removes straw, chaff, dust, and thin corns, leaving only grain likely to produce good malt. Magnets pull out ferrous metals to reduce spark risk and dust explosions. Rotating and shaking sieves separate larger items (straw, un-threshed ears) and smaller ones (sand, thin corns). An aspiration system extracts dust and chaff during sieving. De-stoners or shaking screens remove stones, which are denser and exit the top while cleaned barley exits the bottom. Half-corn separators take out broken kernels, since only one half germinates and produces enzymes. After cleaning, the grain is weighed to calculate cleaning losses, then transferred to a silo.
Storage maintains grain vigour for germination. Malt houses typically use vertical steel or concrete silos, though flat stores handle large amounts.
- Grain moisture after steeping
- 40 to 45%
- Target malt moisture after kilning
- around 5%
- Germination temperature range
- 10 to 16 °C
- Steeping temperature range
- 10 to 15 °C
- Typical silo capacity
- 5,000 to 20,000 tons
- Maximum safe storage moisture
- 13%
- Maximum storage duration
- 18 months
Lore & Background
Malting begins with intake of grain from the farmer, which is cleaned, dried if necessary, and tested for suitability. Traditional floor malting germinates grains in a thin layer on a solid floor, manually raked and turned to keep them loose and aerated. In a modern malt house, the process is more automated, with slotted floors allowing forced air through the grain bed and large mechanical turners like Saladin boxes handling much thicker beds for higher productivity and energy efficiency. The wet process starts with steeping, where grain moisture rises from around 12% to between 40 and 45%, and ends with kilning, which reduces moisture to about 5% and stops germination. During kilning, a curing stage above 80 °C breaks down SMM to DMS, reducing off-flavors, and the Maillard reaction produces color. After kilning, rootlets (culms) are removed and sold as animal feed, and the malt is cleaned and blended into homogenous batches.
Reader's Guide
Malting is the foundational process for brewing and whisky making, as it develops the enzymes needed to convert starch into fermentable sugars. The article describes a standardized base malt protocol, with a piece (batch) as large as 400 tons. Quality checks at intake—including moisture content, nitrogen content, germinative capacity, and absence of fungal growth—ensure only suitable grain enters. Storage in vertical silos (steel or concrete) protects grain from moisture and pests, with temperature monitoring below 18 °C to inhibit insects. The steeping process uses wet stands and air rests with controlled aeration to maximize barley growth, while germination is maintained at 10–16 °C with constant humidified air and mechanical turning. Kilning’s free drying stage preserves enzymes, and the curing stage at over 80 °C reduces DMS potential, an off-flavor resembling sweetcorn in beer. The final malt is cleaned and stored for blending, ensuring consistent quality for brewers and distillers.
Did You Know?
- A batch of malt is known as a piece and can be as large as 400 tons.
- The first visible sign of germination is the appearance of rootlets called 'chit'.
- During kilning, the curing stage above 80 °C breaks SMM down to DMS to reduce off-flavors.
- Half kernels must be removed during cleaning because only one half will germinate and produce enzymes.
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