How Malting Works

Living barley begins to grow, but the maltster stops it before the young plant consumes the starch the distiller needs. This is malting: controlled germination. Barley is soaked, allowed to begin growing, then usually dried. The process develops enzymes that will later help turn starch into fermentable sugar during mashing; kilning stops growth and develops malt flavour and aroma.[1][2][3]

Smoke can add another dimension. The Scotch Whisky Technical File describes peat smoke rising through a wire mesh floor and through the barley, giving the malt its “peat reek”. Peating is optional; controlled germination is the essential work.[1][2]

Why whisky makers need malt

Malting prepares the grain; mashing converts its starch. Encouraging barley to germinate develops the enzymes and prepares it for processing, while the main conversion into a fermentable substrate happens later, at the distillery.[1][2]

The Maltsters’ Association of Great Britain (MAGB) explains what happens inside the grain. Once hydrated, the embryo causes enzymes to be produced that break down cell walls in the endosperm, the starch-containing part of the grain. The maltster must then stop growth before the developing plant consumes the starch the distiller needs.[2]

For Scotch whisky, those enzymes are essential. The Scotch Whisky Technical File requires malted barley and prohibits added enzymes: conversion at the distillery must use only the grain’s endogenous enzyme systems, meaning its own enzymes. These are Scotch requirements, rather than a universal definition of whisky production.[1]

The maltster’s task is a careful balance: encourage enough development to prepare the barley for processing, then preserve useful starch and enzyme activity through the usual drying stage. Malting is much more than drying grain.[2][3]

How malting works, step by step

From barley selection to finished malt, the process has six steps. A 2024 review in the Journal of the Institute of Brewing identifies them as barley selection, cleaning and grading, steeping, germination, kilning, and storage and blending to specification. The table combines selection with cleaning and grading under “Selection and preparation”. Its figures describe modern malting practice; individual programmes vary.[3]

All process figures in this table come from the 2024 review.[3]

Selecting barley that will grow

Malting starts with living grain. MAGB says barley must be capable of germination, and that maltsters buy barley with at least 98% germination.[2]

The intended use of the finished malt also shapes selection. In its account of Scotch distilling malt, Crisp describes Scottish two-row barley used for “Pot Still malt”, names Concerto and Laureate as varieties, and gives typical protein content of 8.5 to 10%. These are Crisp’s published specifications, rather than an exhaustive list of suitable varieties.[4]

Steeping: water, then air

Water wakes the grain. Steeping raises its moisture enough to start germination: the 2024 review describes an increase from 10 to 13% to above 40%, ideally 42 to 45%, through alternating water immersions and dry rests over one to two days.[3]

Air matters too. During the wet phases, the review describes air being blown through the barley so that it can breathe. The dry rests are an active part of controlled hydration, not simply pauses between soakings.[3]

MAGB gives another practical outline: two or three immersions over two to three days, aiming for about 46% moisture. The embryo begins to germinate at around 35% moisture, it says, so growth is already under way before the final moisture target is reached.[2]

The two accounts describe different operating ranges, not a single universal steeping time. In both, water uptake and the start of germination carry the grain from the steep into the next stage.[2][3]

Germination: developing the malt

Once steeped, the barley keeps growing under controlled conditions. In modern pneumatic maltings, humid air passes through the grain. The 2024 review describes moisture held at 42 to 46% during three to five days of germination, ideally at 13 to 16°C.[3]

MAGB gives four to six days, depending on the final malt type. The timing serves the malt: this is managed growth, with the grain developed for its intended use rather than left to grow unchecked.[2][3]

This is where the familiar sight of barley spread across a malting floor belongs. The Scotch Whisky Technical File describes steeped barley being spread over floors; modern equipment uses germination boxes or drums fitted with turners.[1][3]

Kilning: stopping growth and developing flavour

Green malt, the name for the germinated grain, is usually dried before the young plant exhausts its starch reserve. Kilning stops that growth, first drying the malt and then curing it at a higher temperature.[2]

The 2024 review describes an initial withering phase of about 12 hours at 50 to 60°C, followed by higher temperatures reaching 80 to 85°C for pale malt. Finished moisture is 4 to 6% in the review; MAGB gives a broader 3 to 6%, depending on the malt’s use.[2][3]

Heat also builds flavour. The review identifies Maillard reactions during kilning as a source of malt flavour and aroma. Calling malt merely dried barley misses both the biological changes during germination and the flavour development in the kiln.[3]

Useful enzyme activity must survive the heat. Beta-amylase, one of the enzymes involved in starch conversion, survives kilning better than might be expected, the review notes, because the grain is dry and sugary.[3]

The kiln also accounts for most of malting’s energy demand. The review attributes 80 to 90% of total malting energy use to this stage, conventionally supplied by gas. Drying efficiency is therefore a substantial concern in malting technology.[3]

Where peat enters the process

Peat smoke can be introduced during kilning. In the Scotch Whisky Technical File’s account, it rises through a wire mesh floor and through the barley, giving the malt its “peat reek”.[1]

The peat-smoke character described in that production account comes from smoke, rather than peaty water. How much smoke is a choice: the Technical File says commercial maltsters supply malt at levels selected by the distiller, ranging from none to heavily peated.[1]

Malting and peating are distinct processes. Germination prepares the grain for use; smoke during kilning adds an optional influence to the resulting malt.[1][2]

Where malting happens

A distillery does not have to malt its own barley. The Scotch Whisky Technical File says some retain malting on site, while others obtain malted barley from dedicated malting companies.[1]

MAGB distinguishes two types of producer. Distiller maltsters operate maltings for their own distilling needs; sales maltsters make malt to a customer’s specification. A distiller buying malt can therefore set requirements for what it receives.[5]

The scale varies considerably. The 2024 review describes floor-malting batches of under about 40 tonnes, compared with batches of up to around 400 tonnes in modern maltings.[3]

Modern plants use cylindrical or flat-bottomed steeping vessels, circular or rectangular germination boxes, or drums with turners. The review describes kilns fitted with perforated floors and turning rakes. The equipment changes, but the sequence remains: hydration, controlled germination and drying.[3]

The distinctive pagoda chimney belongs to the malt kiln, not the still house. The kiln dries malt, sometimes with peat smoke, after floor malting or another germination process.[1][2]

What distillers ask of finished malt

Extract alone does not tell a distiller enough about malt. Crisp explains that distilling malt is assessed through fermentability and Predicted Spirit Yield, usually shortened to PSY.[4]

The distinction matters because not all extracted material contributes equally to predicted spirit yield. Crisp’s calculation first combines extract and fermentability, then applies a conversion factor to express the result as litres of pure alcohol per tonne.[4]

Its published calculation is:

• Fermentable extract = extract × fermentability ÷ 100.
• PSY = fermentable extract × 6.06, expressed in litres of pure alcohol per tonne.[4]

The calculation helps distillers assess malt by translating extract and fermentability into a predicted spirit yield. In Crisp’s worked example, 78% extract and 86% fermentability give approximately 67% fermentable extract and a PSY of 406 litres of pure alcohol per tonne. This is a prediction used to assess malt, not a statement of actual distillery output.[4]

There is also an important exception to the usual drying sequence. Kilning is not compulsory for every use of malt in Scotch production: the Technical File notes that some grain whisky production uses green, unkilned malted barley mixed with cooked unmalted cereals. Malting’s biological work can therefore serve the distiller without the drying stage that usually follows it.[1]

Where to go next

• Floor Maltings: The Distilleries That Still Do It: explore the distilleries retaining floor malting.
• How Peat Is Cut and Burned for Malting: follow the fuel used to smoke malt.
• Why Do Scottish Distilleries Have Pagoda Roofs? Charles Doig's Story: understand the architecture associated with malt kilns.

Sources

1. UK Government. Technical File for Scotch Whisky, June 2019. https://assets.publishing.service.gov.uk/media/5fd36667e90e07662ed92c85/Scotch_Whisky_Technical_File_-_June_2019.pdf

2. Maltsters’ Association of Great Britain. How malt is made, undated web page. https://www.ukmalt.com/uk-malting-industry/how-malt-is-made/

3. Evans, D. E., Shen, W. and Brookes, P. A. Malting, ‘the middle parts of fortune’: a history of innovation and the enduring quest for efficiency. Journal of the Institute of Brewing, volume 130, issue 3, pages 126 to 181, 2024. doi:10.58430/jib.v130i3.58. https://jib.cibd.org.uk/index.php/jib/article/view/58

4. Crisp Malt. Scotch Distilling Mash Procedure, undated PDF, maltster’s account. https://cdn.shopify.com/s/files/1/0002/9006/2342/files/Crisp_Malt_Scotch_Distilling_Mash_Protocol.pdf

5. Maltsters’ Association of Great Britain. UK malting industry, undated web page. https://www.ukmalt.com/uk-malting-industry/

This desk-researched article uses the site’s verified fact sheet, drawing on the Scotch Whisky Technical File, an academic review, industry-body explanations and an attributed maltster’s specification.

Last checked: November 2026