What is malting?
Malting is the controlled germination of barley grain, followed by drying, to produce malt — the essential fermentable material used in brewing, distilling, and food production. The process activates enzymes naturally present in the grain and produces the compounds that brewers need to convert starch to fermentable sugar during mashing.
The key outputs of a successful malting process are: a modified grain with degraded cell walls, active starch-converting enzymes (particularly alpha- and beta-amylase), appropriate moisture content, and a stable, storable product with the color and flavor characteristics required by the buyer specification.
Core transformation: Malting converts dormant, starchy barley grain into an enzymatically active, partially modified substrate that brewers can extract efficiently. Without malting, barley starch is largely inaccessible to yeast.
Step-by-step: the four stages
Receiving, Cleaning & Storage
Raw barley arrives at the malthouse and is cleaned to remove dust, stones, broken grains, and weed seeds. It is graded by kernel size (typically over 2.5 mm screen). Barley must rest in storage for a minimum dormancy period — usually 4–8 weeks after harvest — before malting. Dormant barley will not germinate evenly, resulting in unacceptable malt.
Moisture at intake: ~12–14% | Storage temp: 15–18°CSteeping
Cleaned barley is loaded into steep tanks and alternately soaked in water and exposed to air over 48–72 hours. The water absorption raises moisture content from ~12% to 42–46%. Steeping triggers enzymatic activity and initiates germination. Water temperature, aeration intervals, and steeping duration are precisely controlled to achieve uniform moisture distribution and initiate chitting — the visible emergence of the rootlet tip.
Duration: 48–72 h | Target moisture: 42–46% | Temp: 12–18°CGermination
Steeped barley moves to germination vessels — floor maltings, box maltings, or drum maltings — where the grain is kept at 15–20°C for 3–6 days. During germination, the embryo produces gibberellins (plant hormones) that signal the aleurone layer to synthesize and secrete hydrolytic enzymes. These enzymes — including alpha- and beta-amylase, protease, beta-glucanase, and limit dextrinase — attack the starchy endosperm and cell walls, achieving "modification." Rootlets and the acrospire develop visibly. The maltster monitors acrospire growth (targeting 75–100% of kernel length) as a modification indicator.
Duration: 3–6 days | Temp: 15–20°C | Acrospire target: 75–100% kernel lengthKilning
Green malt — the germinated, high-moisture grain — is transferred to the kiln and dried with heated air. Kilning has two phases: the initial drying phase (free drying) reduces moisture from ~44% to ~10% at low temperature (50–60°C) to preserve enzyme activity. The curing phase applies higher temperatures (65–105°C for pale malt) to reduce final moisture to 3–5%, fix enzymes, destroy the rootlets, and develop the color, aroma, and flavor compounds characteristic of the malt type. Higher kiln temperatures produce darker malts with more Maillard reaction products.
Drying: 50–60°C | Curing: 65–105°C | Final moisture: 3–5%Deculming & Finishing
After kilning, the dried rootlets (culms) are mechanically separated from the malt in a deculmer. Culms are bitter, high in protein, and undesirable in the finished product. They are collected as a valuable animal feed co-product (high in protein and B vitamins). The finished malt is screened, cleaned, cooled, and transferred to storage silos. Samples are taken for analytical quality control before the malt is released for sale.
Culm moisture: 6–8% | Malt final moisture: 4–5% maxKey quality parameters after malting
The finished malt is evaluated against a specification that reflects the buyer's requirements. Typical parameters include:
| Parameter | Typical range (pale lager malt) | Significance |
|---|---|---|
| Moisture | ≤ 4.5% | Storage stability and shelf life |
| Extract (dry basis) | 78–82% | Fermentable yield potential |
| Total protein | 9.5–11.5% | Enzyme activity and foam stability |
| Diastatic power | ≥ 220°WK | Starch conversion capacity |
| Alpha-amylase | 40–70 DU | Liquefaction of starch |
| Beta-glucan (wort) | ≤ 150 mg/L | Filtration and processing efficiency |
| Kolbach index | 38–42% | Degree of protein modification |
| Homogeneity | ≥ 92% | Uniform modification across the batch |
| Color (EBC) | 2.5–4.5 | Beer color contribution |
Malt types: beyond pale malt
While pale lager malt (also called base malt) is the most widely produced, the kilning process can be modified to produce a spectrum of specialty malts used in beer color, flavor, and body development:
- Pilsner malt: Lightest base malt, minimal kilning. Standard for lager brewing.
- Vienna malt: Slightly darker, kilned at higher temperatures. Toasty, biscuit character.
- Munich malt: High kilning temperature. Deep amber color, strong malt aroma.
- Crystal/Caramel malt: Stewed before kilning to convert starch to non-fermentable dextrins inside the kernel. Adds sweetness and body.
- Roasted malts: Kilned at very high temperatures (200–230°C). Used in dark beers for coffee and chocolate notes.
- Distilling malt: Higher enzyme activity. Optimized for spirit conversion efficiency.