Practical aspects of manufacturing malt for brewing

Independent Brewers Association Beer News, Technical Article









Ken Steer-Jones MDip

Contributions from Alan Brown, Bob McWilliam, Mark Kinsman, Ben O’Gorman

Barley has been malted for over 3,000 years.  It is a natural process, the basic principles of which have changed little over hundreds of years.  But only in the past 50 years or so have maltsters taken full control, thanks to a proper understanding of the biochemistry, suitable varieties and modern equipment.  The maltsters’ art is to use natural ingredients to produce a consistent quality of malt that will provide the brewer with the basic components for the brewing process.

Barley, water, air, heat are all that is used to make malt.  There are three basic stages in the malting process, steeping, germination and kilning.  Malting is the controlled rehydration and germination of barley, followed by a termination of this natural process by the application of heat.

The maltster’s task is to create enzymes that will degrade the protein matrix and cell wall material so that, at the end of the malting process, the starch in the malt is readily available to the Brewer and this process is called modification.  The malt also provides a source of specific enzymes which are responsible for the breakdown of starch into fermentable sugars in the mashing process.


It is essential the maltster selects the best quality barley to meet the demands of modern brewing practice.  The maltster has to maintain product consistency of the highest quality standards to provide material that will essentially provide a source of starch that ultimately will be converted into alcohol as well as flavour and colour in the final beer.

A barley breeding programme has been well established which has focused on the development of varieties that will meet the exacting standards for brewing but still maintain high agronomic yields making them attractive to the farmers and also be sufficiently robust to be able to withstand the vagaries of the UK climate.  The main goals for the cereal breeder in terms of producing barley for malting are:

  • Greater yield per hectare
  • Rigid straw which is resistant to lodging
  • Ears that can withstand mechanical harvesting and do not shatter
  • Enhanced disease resistance
  • Improved grain size, uniformity / homogeneity
  • Enhanced extract yield
  • Ease of malting and optimising malt yield

Although each variety may have its own particular characteristics which will determine how it performs agronomically and in the maltings, some of the main recognised barley quality factors for brewing malt production are as follows:

  • Displays good, even recovery from natural in built dormancy
  • Is generally a low nitrogen accumulator
  • Uniform corn size
  • Good husk cohesion, not susceptible to skinning.
  • Demonstrates good mould resistance, low susceptibility to mycotoxin contamination
  • Not susceptible to pre-germination
  • Resists splitting at any stage
  • Viable grain with no dormancy issues

Attributes required from malting barley include:

  • Homogeneous and vigorous germination
  • Mealy, not steely, endosperm to allow rapid even water uptake (hydration) during the steeping process
  • High starch content, more available starch to convert to alcohol
  • Demonstrate ability to achieve low levels of residual beta-glucan after malting
  • Ability to produce a sufficient level of enzymes for starch conversion
  • Uniform corn size, gives consistent milling characteristics

Barley varieties are rigorously tested over several years and will only be used for malting once approved specifically for malting use and of the many varieties that show potential only a very few achieve final approval.  This process is overseen by the Malting Association of Great Britain and involves all the UK malting companies.  The 2018 current approved list of malting varieties can be viewed at


The role of purchasing is to ensure the correct raw material quality and volume is collected to meet customer needs and maintain malting site steeping cover.  Factors influencing barley procurement include:

  • Supply and demand, UK, European, Global
  • Pricing impact of feed barley, wheat, imports and exports
  • Variety selection, yield and malting potential
  • Harvest weather conditions and barley corn size
  • Malt House intake speed, drying and storage capacity
  • Government involvement and intervention.

Barley is sourced indirectly from farmers through grain merchants who act as intermediaries or brokers between the farmer and the maltster to ensure that barley of the right quality and volume is offered to the maltster at a price that is acceptable to both parties.  Bairds Malt has its own in house merchanting arms (Saxon Agriculture, MLG and Scotgrain) that work with the farmer from the moment the raw seed is sown through the growing, harvesting and delivery of the barley to the maltings.  This gives Bairds an insight into agronomic aspects of the barley crop as well as being able to develop long term relationships with farmers that will provide barley at the right quality consistently over many years.




This is the most important stage of the malting process. Mistakes made during this period are very difficult if not impossible to correct later.

Steeping raises the moisture content of the barley grain to initiate and sustain germination when enzymes start to ‘modify’ the starchy endosperm.  The main factors affecting the steeping process include:

  • temperature
  • grain size
  • protein content
  • viability
  • variety
  • crop year

Water uptake is initially purely a physical process and therefore temperature dependant within physiological boundaries for germination.  After germination water uptake by the barley grain becomes an active process.  Small thin grains will take up water fastest and to a greater extent therefore an even grain size of 2.5mm – 2.8mm is preferable.  Water uptake rate during steeping is related to protein (or nitrogen) level.  Lower nitrogen levels tend to be associated with ‘mealy’ barley which take-up steep water more quickly.

Only viable (living) grain should be steeped.  Maltsters will check barley has a germination capacity of at least 98% before putting forward for steeping.

Maltsters use immersion steeping with periods of air rest (breaks), aided by forced ventilation, which allows oxygen to reach the grain to accelerate germination.  Modern malting varieties are able to absorb water more rapidly.  The rate of water uptake can be can be increased by lengthening air breaks.  The length of the air breaks, especially later in the steep cycle must be determined by the balance between the heat being produced by the grain due to respiration and the cooling effect of the ventilation system.  Typically steeping will take place over a 48 – 60 hour period involving two or three water immersions.  The steep cycle will depend on barley quality, variety and malting plant configuration.



The germination stage of the malting process is when the structure of the endosperm cells are changed by the actions of enzymes produced by the embryo.  This change is known as modification.  Three sets of enzymes are principally involved, the first the glucanases, break down the cell wall which primarily consists of β-Glucan.  Proteases can then start to break down the proteins that encompass the starch granules to produce soluble, smaller molecular weight proteins, peptides and amino acids.  The third set of enzymes involved are the amylases which will break down the starch into fermentable sugars although most of this will this occur in the mash tun.


Some of these enzymes are very sensitive to heat and will be denatured during the kilning process so it is essential that the modification process has been completed before the kilning stage starts.  If not there may be quality issues with the malt especially if the cell wall material has not been degraded as this can cause run off problems after mashing.  Protein needs to be sufficiently modified to produce nutrient for the multiplying yeast cells during fermentation and to ensure that all the starch is available for the amylase enzymes.  Germination temperatures are controlled by forced air ventilation that keep the germination grain cool that optimises the enzyme actions taking place.  The ventilation air is normally humidified so that the air passing through the germinating grain does not remove moisture introduced in to the grain during the steeping phase.





The three principal objectives of kilning distilling malt are to halt the germination process, reduce moisture content for long-term storage and preserve enzyme activity potential in order to maximise malt fermentability.  By happy coincidence the kilning process also allows for the development of flavour, aroma and colour which are highly desirable in brewing.

Kilning is achieved by passing warm air through the malt bed using a temperature profile.

The physical phases of kilning are free, forced and curing.  The temperature and humidity profiles during each of these stages are shown in the chart below.

The main aim during kilning in terms of malt quality is to preserve the enzyme potential by ensuring an even airflow and controlling temperature gradients through the bed.  These enzymes are crucial for the production of fermentable sugars during mashing which ultimately are used by the yeast during fermentation to produce alcohol (see malt specification).  Enzymes become more stable at low moisture levels in the malt and this allows for more heat to be applied particularly during the curing phase and this allows for the desirable components of flavour and colour to be developed as well as aroma.


Malt colour develops through the well known but complex Maillard Reaction whereby amino acids and sugars react together when heat is applied forming both colour and flavour compounds.  In essence the higher the temperature the more flavour and colour that will develop.  Lightly coloured lager malts are kilned at gentler, lower temperatures than darker pale ale, Vienna or Munich malts which are kilned more aggressively using higher curing temperatures.


Roasted Malts

Roasted malts is a group of special types of malt that are produced from either fully germinated but unkilned grain or finished kilned malt that have been literally roasted at high temperatures in large drums which are essentially large coffee roasters.  Depending on the temperature and time applied a range of colours from light toffee to very dark/black are developed.  Equally, flavours are also highly developed ranging from malty caramel to very acrid/bitter or astringent, close to but not quite burnt.  These malts are used by the brewer for colour adjustment as well as providing particular flavour profiles in various beer styles.  Used in differing amounts and colours the impact on beer styles varied and can be likened to an artist mixing colours on a pallet.  Other benefits include contributions to aroma, mouth feel and control of beer oxidation.

There are three starting points for roasted product.  These are barley, germinated grain or finished kilned malt.  Cara and crystal are produced from fully germinated but unkilned grain which is loaded in to the roasting drum where it is warmed to allow the enzymes in the grain to fully convert or saccarify the starch into sugars.  Once saccarification is complete heat is applied until the sugars become crystalised and depending on amount of heat and time, colour and flavour is developed.  The resulting Maillard Reaction that develops the colour and flavour can be extremely fast and it is the skill of the roast operator that controls the final outcome.

The darker roasted malts such as chocolate and black use finished lager malt but as there are relatively few enzymes and little moisture present the saccarification process is bypassed so a different pathway in the Maillard Reaction produces the desired colours and flavours.

Roast barley is produced from unmalted barley and using processes similar to those that produce chocolate and black.


Brewing Specifications

Tests use to measure malt quality, typically quoted in a brewing malt specification are designed to give an indication of how the malt will meet the brewer’s demands i.e. extract and alcohol yield, protein and cell wall modification, enzyme potential and level of certain flavour characteristics. Typical specification can be broken down into these constituents as follows:


The reasons why these parameters appear in the malt specification and their significance to the maltster and brewer can be defined as follows:

Moisture: Reduce water content to acceptable levels suitable for safe storage and achieve optimum milling characteristics.
Extract: Provides a fermentable source for yeast growth. Contains carbohydrate soluble protein, FAN (Free Amino-Nitrogen) and trace vitamins/elements.
Total Nitrogen: Less protein equates to more starch and therefore potentially higher achievable extract. Contributes to head retention, impacting mouth feel and palate of the final beer.
Wort Colour: Colour of malt extract which will impact on final beer colour and is dependent on malt type.
S/N / FAN: Soluble protein and FAN are necessary for yeast growth and the production of new yeast cells during fermentation.  FAN level I dependant on total nitrogen and soluble nitrogen.  The FAN component assimilated by yeast at start of fermentation and helps to kick start fermentation and also determines fermentation rate.
Friability: Friability gives an indication of the level of well modified malt fraction.
Whole corns: Whole corns gives level of dead barley corns where no modification occurred during processing.  High levels cause brewery processing problems associated with B-glucan.
Homogeneity: Measures the evenness of modification.  Indicates the extent of patchy modification or unmodified large grits of endosperm.  Also associated with problems associated with B-glucan.
Residual B-glucan: Primary objective of maltster is to achieve complete degradation of endosperm cell wall – B-glucan.  Residual malt/wort B-glucan causes major brewhouse processing problems and may lead to poor/slow wort run off, poor extract yield and in extreme cases cause a set mash.  It may also contribute to beer haze problems and with difficulties in achieving beer clarity.
Diastatic Power: Measurement of potential starch degrading enzymes that will convert starch to simple fermentable sugars.  Combination of alpha and beta amylase activity.
Dextrinising Units: A measure of alpha amylase that randomly hydrolyses starch into shorter chains and contributes to rapid reduction of wort viscosity.


Food Safety

As part of the quality aspect of malt, the maltster must also consider the food safety implications of the malt.  The main food safety issues that impact on the quality of the raw material is possible contamination by:

  • residual pesticides levels following any treatment of the barley
  • mycotoxins produced from moulds forming on the barley during storage
  • residual heavy metals pick up from contaminated soil

The risks related to these issues can be controlled and reduced by the adoption of a management system that will demonstrate the use of assured grain from a recognised source and show traceability through the supply chain from source to bulk storage and to delivered malt.

However an aspect related to food safety which impacts on malt quality and occurs during malt processing is the introduction of NDMA (Nitroso-dimethylamine).  NDMA is a potential carcinogenic substance produced in trace amounts as a by-product of the kilning process.  Oxides of nitrogen (NOX gases) are formed during combustion of fuels such as gas and oil.  Amines, particularly dimethylamine and to a lesser extent hordenine, occur naturally in cereals and increase during germination, concentrating in the rootlets and acrospires.  In directly fired kilns, where combustion gases come into direct contact with the grain bed, these amines can react with NOX gases to form nitrosamines, mainly NDMA.

Methods used to control and maintain low levels of NDMA:

  • Indirect fired kilning (best option)
  • Burning of sulphur
  • Use of low NOx burners

It should be noted that the typical levels of NDMA detected in malts are negligible due to the malting industry moving to use of indirect kilning in recent years.



The modern day maltster has many challenges but with the application of science behind barley variety selection and malting biochemistry together with new malting plant engineering and environmental strategies we will ensure a sustainable supply of raw material for the craft brewing industry of the future.


Article Sponsored by: Bairds Malt







Bairds Malt have almost 200 years of producing Quality Malt to the world’s leading brewers and distillers.  For more information, check out our website at