The Malting Process: How Barley Becomes Malt, Step by Step

The short answer: malting turns raw barley into malt in three steps: steeping the grain in water, letting it germinate for a few days, then kilning it dry with hot air. Germination builds the enzymes brewers rely on (alpha- and beta-amylase, proteases, beta-glucanase) and softens the hard kernel so its starch can be reached. Kilning stops the growth, protects the enzymes and sets the malt’s colour and flavour. The starch itself is turned into sugar later, in the brewer’s mash.

Stage	Time	What happens
Steeping	1–2 days	Grain soaks in water, with air rests, to about 42–46% moisture, which wakes the embryo
Germination	4–6 days	Enzymes form; cell walls and proteins break down so the starch becomes accessible (“modification”)
Kilning	1–2 days	Hot air dries the malt to about 4% moisture. Low heat keeps pale malt enzyme-rich; more heat makes darker, more flavourful malts

Why barley has to be malted

A barley kernel is mostly starch, packed inside hard cell walls and a protein matrix. Yeast can’t ferment starch, and raw barley has almost none of the enzymes needed to break it down. Malting is controlled sprouting: the seed is tricked into starting to grow, which makes it build those enzymes and soften its own insides, then it is dried before the young plant uses up the starch. The brewer finishes the job in the mash, where the enzymes turn the starch into sugar.

Step 1: Steeping

The maltster soaks clean barley in water, alternating wet periods with air rests, for one to two days. The kernel absorbs water until it reaches about 42 to 46% moisture. The embryo needs oxygen as well as water to wake up, which is why the air rests matter: a grain that is kept under water too long suffocates. By the end of steeping, a small white rootlet, called the chit, appears at the base of each kernel.

Step 2: Germination

The wet grain is spread out in cool, humid, well-ventilated beds, usually at about 59 to 68°F (15 to 20°C), and turned regularly for four to six days. This is where the biochemistry happens:

1. The embryo sends a signal. It releases plant hormones called gibberellins, which travel to the aleurone, a thin layer of living cells around the starchy endosperm.
2. The aleurone makes enzymes. It produces alpha-amylase, beta-glucanase and proteases and releases them into the endosperm. Beta-amylase is already stored in the endosperm in an inactive, bound form, and is released during germination.
3. The kernel is “modified.” Beta-glucanase breaks down the gummy cell walls, and proteases break proteins down into smaller proteins, peptides and amino acids. The kernel goes from hard and glassy to soft and crumbly.
4. The maltster stops at the right moment. The shoot inside the husk, the acrospire, grows along the kernel. When it reaches about three-quarters to the full length of the grain, modification is complete. Going further only lets the plant burn starch the brewer wants.

Modification is the key idea in malting. Well-modified malt mills easily, releases its starch readily and lauters well. Almost all modern base malt is fully modified, which is why most beers today need only a single-temperature mash.

Step 3: Kilning

Kilning dries the “green malt” with hot air, in two phases:

• Withering (drying). Warm air, about 120 to 140°F (50 to 60°C), removes most of the water while the grain is still moist. Keeping it cool while it is wet protects the enzymes, which are easily destroyed by heat when wet.
• Curing. Once the malt is dry, the temperature rises to set the colour and flavour: roughly 175 to 185°F (80 to 85°C) for pilsner malt, a little hotter for pale ale malt, and up to about 220°F (105°C) for Munich malt. At these temperatures sugars and amino acids react in Maillard reactions, the same browning chemistry as toasting bread, creating colour and bready, toasty and malty flavours.

After kilning, the dry rootlets are knocked off, and the malt rests for a few weeks before it is sold. The curing temperature also explains a brewing detail: pale pilsner malt is cured cool, so it keeps more of the precursor of DMS, the compound that tastes like cooked corn. That is why pilsner recipes call for a longer, rolling boil.

The enzymes malting builds

Enzyme	What it does	Works best in the mash at
Beta-glucanase	Breaks down gummy beta-glucans from cell walls, for easier lautering	95–113°F (35–45°C)
Proteases and peptidases	Break proteins into peptides and amino acids that feed the yeast	113–131°F (45–55°C)
Beta-amylase	Snips maltose off the ends of starch chains: highly fermentable sugar	140–149°F (60–65°C)
Alpha-amylase	Cuts starch chains in the middle, making dextrins and opening more ends for beta-amylase	158–162°F (70–72°C)

A mash temperature near 149°F (65°C) favours beta-amylase and gives a dry, fermentable wort; near 156°F (69°C) favours alpha-amylase and gives more body. See our mash temperature chart and step mashing guide.

How different malts are made

Malt	Colour (°L)	How it’s made	Character	Enzymes?
Pilsner	1.5–2	Kilned cool	Light, grainy, clean	Yes, plenty
Pale ale	2.5–3.5	Cured a little hotter	Slightly toasty base malt	Yes
Vienna	3–4	Cured hotter still	Light toast	Yes
Munich	6–10	Kilned warm and moist, then cured hot	Rich, bready, malty	Some; converts itself
Crystal / caramel	10–120	Green malt is “stewed” wet at mash temperatures so the starch turns to sugar inside the husk, then dried or roasted	Caramel sweetness, body	No
Chocolate	300–450	Pale malt roasted in a drum	Roast, cocoa, coffee	No
Black malt / roasted barley	500+	Roasted very dark; roasted barley is unmalted	Sharp roast, colour	No

Malts with enzymes can convert their own starch in the mash. Crystal and roasted malts can’t, so they always go in alongside a base malt. For choosing malts for a recipe, see our guide to brewing malts and how roasting changes flavour.

How malting shapes the beer

• Colour and flavour come from kilning and roasting.
• Fermentability and body depend on the enzymes the malt brings and on how you mash it.
• Yeast health depends on the amino acids released during malting and mashing.
• Foam and haze depend on the proteins and beta-glucans left in the malt.
• Brew-day ease depends on modification: well-modified malt mills, mashes and lauters easily.

Can you malt barley at home?

Yes, though it takes about a week and some space. Steep the barley in a bucket, changing the water and draining it for air rests, until it chits. Spread it on trays and turn it a few times a day until the acrospire is about three-quarters of the kernel’s length. Then dry it in an oven or food dehydrator at about 120°F (50°C) until it’s crisp, and finish at about 175°F (80°C) for pale malt. Most brewers buy malt, but home malting is a satisfying project, and it’s the only way to brew with grains no maltster sells.

Frequently asked questions

What is malting?

The controlled germination and drying of cereal grain, usually barley. It builds the enzymes and softens the grain so brewers can turn its starch into fermentable sugar.

Does malting turn starch into sugar?

Only a little. Malting builds the enzymes and makes the starch accessible; the conversion into fermentable sugar happens in the brewer’s mash. Crystal malt is the exception: it is stewed so the conversion happens inside the kernel.

How long does malting take?

About a week: one to two days of steeping, four to six days of germination and one to two days of kilning.

What is modification?

How thoroughly the grain’s cell walls and proteins were broken down during germination. Fully modified malt, which is nearly all modern base malt, works with a simple single-temperature mash.

What is the difference between malted and unmalted barley?

Malted barley has enzymes and a soft, crumbly interior. Unmalted barley is hard, has few enzymes and must be mashed with malt to convert. Flaked and roasted barley are unmalted.

Why is barley the main malting grain?

It has plenty of enzymes, a husk that forms a natural filter bed in the mash, and a good balance of starch and protein. Wheat, rye and oats are malted too, usually as a smaller part of the grain bill.