Russell I. (ed.) Whisky. Technology, Production and Marketing
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and bred for southern climes were likely to show severe dormancy periods of
up to sixteen weeks. From 1980, the spring barley Triumph gained ground as it
gave much improved spirit yields, but it could remain dormant for up to 26
weeks. While dormancy can be reduced by appropriat e storage conditions (see
later), the constraints of having to dry and store barley on site at harvest are a
severe financial limitation to Scottish maltsters. In spite of this, the benefits are
substantial. By guaranteeing quality and variety and minimizing drying and
storing costs rather than paying a merchant or farmer to perform this critical
task, Scottish maltsters have been able to provide consi stently high-quality
distilling malts. The mild climate and high latitude day length generally pro-
duce plump barley with high thousand-corn weight and a relatively low total
nitrogen (TN) content (about 1.6–1.7 per cent). On the other hand, the overall
growing period is relatively short, with spring barley (genera lly sown in early
March) being harvested in late August to early September.
For around twenty years (1965–1985) Golden Promise (GP) was the major
variety in use. Despite being very susceptib le to attack by mildew (SAC, 1988)
and thus never bec oming a recommended variety, GP has several attributes
that are still necessary for a variety to be successful in Scotland:
. It is early maturing and more likely to be fully ripe at the end of the short
Scottish growing season
. It has a short, stiff straw, and can resist ear loss during the autumnal gales
prevalent towards the end of the harvest season
. It is not prone to dormancy
. It has malting quality superior to all of its predecessors either in te rms of
extract potential or in ease of processing in the maltings and the distillery.
The success of a barley variety can be gauged by its lifetime in the seed market.
It is now almost 50 year s since the first commercial crops of GP were har-
vested. As new varieties with higher agronomic and distillery yields, such as
Triumph and its successors, were bred and launched into the farming scene
from 1980 onwards, GP waned to a very small tonnage. It was, and remains in
the second millennium, favoured by a handful of distillers, and in the year
2000 over 10 000 tonnes were harvested. In the 1980s, several new varieties that
could outyield GP on the farm and outclass it in te rms of malting quality and
distillery yield were introduced. In particular, the variety Triumph, which was
widely grown throughout Europe, gained in popularity, but it had several
drawbacks. It was not as early maturing or as stiff-strawed as GP, and its
resistance to mildew broke down. Its greatest weakness was its genetic inheri-
tance of severe dormancy – it could be dormant for up to six months after
harvesting. Several hybrids of Triumph, such as Corgi, Natasha and
Camargue, became available in the mid 1980s. These varieties had the benefit
that they did not inherit the sever e dormancy character whilst also having the
agronomic properties or earliness of GP. It was reported that early ripening is
linked to lower dormancy levels for any variety, and this must be of primary
importance in Scotland (Bathgate, 1987). There is no value in barley having
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low TN content and high thousand-corn weight if it cannot germinate when
required.
The extra storage costs of carrying stocks over from the previous harvest, to
cover production requirements during the dormancy period, put a severe
financial strain on Scottish maltsters, and in the late 1980s fervent efforts
were made by plant bre eders to produce varieties that were not prone to
dormancy and gave better distillery yields. Other research at that time showed
that transferring newly dried barley into storage while it was still warm led to
a reduction in dormancy.
In the 1990s plant breeders were being given strong guidance by the
Institute of Brewing (IOB) Barley Committee (BC) regarding the desirable
attributes in barley destined for malting, (brewing) and distilling (note that
the IOB is now called the IGB – Institute and Guild of Brewing), and were
responding by breeding with these requirements in mind. In 1995 the malt-
distilling sector provided the following consensus view of desirable barley
attributes, which still pertains (Brookes, 1980):
1. High priority
. Resi stance to splitting at any stage
. Mea ly, not steely, endosperm
. Rapid, even water uptake (hydration)
. The quality of low nitrogen pick-up when growing
. Vigo rous germination
. High starch content
. Low glycosidic nitrile potential.
2. Medium priority
. Good and uniform corn size
. Good husk appearance
. Ripe ns evenly in the northern UK
. Low dormancy
. No pre-ge rmination.
Barleys that meet these requirements are much more likely to be bought for
malting, as the malt in turn will be more likely to posse s the attributes required
of it when it is considered as the raw material for mashing.
In the 1990s liaison between malt distillers, maltsters, farmers, other inter-
ested parties and breeders became closer, and as a result of all parties under-
standing the attributes required in malt for producing malt whisky, the
breeding programmes were more focused. In the decade, a succession of
new varieties appeared that had the desired agronomic and processing
qualities. Spring varieties have been the most successful, and examples
include Chalice, Chariot, Decanter, Derkado, Optic and Prisma. Winter vari-
eties that have been successful, mainly in southern Scotland, are Melanie,
Halcyon and Regina. During the twentieth century, Scotch malt distillery
yields increased from around 300 l of pure alcohol per tonne of malt dry
weight (abbreviated to l/t (dwb)) to more than 460 l/t (dwb) (see Table 2.6).
This was mainly due to increases in the fermentable extract contents of the
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successive varieties, but also to changes in agronomic and processing prac-
tices (Dolan, 2001) The malti ng aspects of the various varieties are discussed
below, under Malting.
Regarding barley procurement, the high cost of transport from England and
continental Europe, the presence of high-capacity, low-cost maltings near the
major malt whisky distilleries, and the ongoing local availability of malting
barley with the required attributes should ensu re the future of this sector of
the malting industry in Scotland.
Barley storage, cleaning and grading
When the barley has been dried to 12 per cent moisture, it is transferred
directly to store, without cooling, to facilitate dormancy breaking. The tem-
perature of the grain may be between 188C and 258C at this stage, depending
on the expected degree of dormancy. In the Triumph era of severe dormancy,
it was suggested that the temperature should be increased to around 308C for a
short period as a way of lessening the duration of the dormancy (Palmer and
Taylor, 1980). This practice was found to be successful, and has been the
industry norm for about fifteen years. During this period of storage samples
are taken regularly for determination of germination energy, and once dor-
mancy has fully broken the grain bulk is gradually cooled to an ambient
temperature of about 58C for storage over winter. Volumes of air of around
0.15 m
3
/min per tonne are normally used to cool barley, applied either by
Chapter 2 Malt whiskies: raw materials and processing 37
Table 2.6
Major improvements in Scotch malt whisky spirit yields – dates and
causes
Year Spirit yield, l/t
(dwb)
Spirit yield
improvement
Comment
1900 300 – Chevalier in use
1910 300 – Spratt Archer in use
Plumage Archer in use
1950 350 50 Advent of Proctor and Maris Otter
1965 390 40 Advent of Golden Promise
1970 410 20 Effective cleaning and sanitization
introduced
1990 430þ 20 Advent of Triumph
1995 445 15 Advent of Chariot
1997 460 15 Vintage quality Chariot Harvest
2001 460 – Next breakthrough awaited
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pressure fan through ducts under the barley or by suction from above the
bulk. Suction has the disadvantage of being liable to air leaks in the adjoining
structures of the storage vessel, so air could be sucked through the fans with-
out passing through the grain bed. Blowing under pressure suffers the dis-
advantage that, if the grain is sufficiently warm, the air passing through the
grain can absorb additional moisture, which will condense on the roof of the
vessel if it is cold. Condensation droplets failing back on to the grain can cause
severe spoilage on the surface layer of barley.
The types of storage vessel in use vary, but the cheapest form is flat-floored
storage sheds with underfloor ventilation, followed by circular, steel, flat-
bottomed bins with sweep auger clearing and underfloor ventilation.
Concrete silos were constructed in the 1960s when costs were relatively low,
but such silos are presently about five times more expensive to construct than
flat stores. The flat stores are roofed with a gable angle the same as the natural
angle of repose of the barley they contain, so that the wall heig ht is kept to a
minimum. Circular, steel, hopper-bottomed vessels are almost as expensive as
concrete silos, but have the advantage of easy discharge. The major disadvan-
tages of flat stores are in the discharge of barley from flat store and the inabil-
ity to segregate different grades or varieties of barley. Normally barley is
discharged by tractor shovel, which is slow and labour-intensive. Barley vari-
eties can be segregated to a limited degree by insertion of temporary walls, but
if this is done the capacity of the store is lessened.
In some cases, barley is pre-cleaned prior to drying. This pre-cleaning is
usually a rough dressing to remove rubble, straw residues and awns from
the green barley. Since wet barley is particularly difficult to sieve, most
maltsters clean the barley after drying, when it is en route to storage silos,
or after storage en route to steep. Cleaning prior to storage has the advantage
of creating a dust-free environment in the silo, which improves aeration and
working conditions generally but raises the problem of disposing of the
dressings at harvest. The alternative of cleaning prior to steep allows for
sale of the dressings over a longer time period, and this may have some
commercial advantages, but the accumulation of dust and small grains
within the bulk makes it more difficult for the aeration fans to give an
even airflow through the barley.
When the barley is cleaned and graded, the fractionation of the grain size
varies between maltsters. Generally, barley is initially sieved over 2.2-mm
screens and all material less than 2.2 mm in diameter is sold for animal feed.
The EBC recommended method used is Analytica EBC Barley 2.7 (1975).
The main bulk may then be fractionated over a 2.5-mm sieve, depending on
the final mal t quality required. Barley between 2.2 mm and 2.5 mm in dia-
meter amounts to 10–20 per cent of the total, depending on the crop year,
and may have a little higher TN content than the head corn. When malte d
separately the small corns yield between 4 and 5 per cent less extract than
the head corns, have a faster water uptak e and modify about one day more
rapidly than the less than 2.5-mm fraction. It is common to malt small
corns separately because of the differences in steeping and germination
requirements.
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Barley intake quality control
Control of barley variety
The selection of barley varieties for malting depends on availability, cost and
end use of the malt. As with barley, in 1995 the IOB Barley Committee drew up
a prioritized list of desirable attributes in malted barley destined for the
production of malt spirit. There are other attributes in malt destined to be
grain spirit (see Chapter 3). The attributes for malt spirit are:
1. High priority
. High hot water extract (hwe) over a range of TN contents
. High fermentability content
. Low gelatiniz ation temperature
. Rapid, even and complete modification
. High predicted spirit yield (PSY).
2. Medium priority
. Low malting loss during pro cessing
. The required pentose/pentosan balance
. Resistan ce to myco toxins.
The attributes desired in the malt feed back to the attributes desired in the
barley (see above), and are strong guidelines for the breeders.
Each year in the UK, a list of recommended cereal varieties is produced by
the Cereal Trials Advisory Committee (CTAC) of the Home Grown Cereals
Authority (HGCA) (HGCA, 2000). It takes into account the agronomic and, for
barleys, the malting performance, wh ich is judged from extensive micromalt-
ing studies. From this list, the Scottish Agricultural College (SAC) produces a
list for the northeast and northwest regions of the UK, within which lies
Scotland (SAC, 2001). Varieties are ‘approved’ (IGB, 2001)**5 after further
extensive micromalting, macromalti ng and distilling trials by the Institute
and Guild of Brewing (IGB) Barley Committee (BC). Growers select suitable
varieties from these lists for growing in Scotland and northern England, for
acceptance for malting, providing they are of the required quality at harvest.
In 2001 the approved varieties were:
. Winter barleys – Regina
. Spring barleys – Chalice, Chariot, Decanter, Derkado, Optic and Prisma.
Some barley varieties that are on the IGB list and are important in the distilling
industry produce cyanogenic glycosides, including methyl glycoside in their
growing tips (Riffkin et al., 1989a, 1989b, 1990; Cook, 1990; Cook et al., 1990).
Methyl glycoside is a chemical precursor of the compound ethyl carbamate,
which is a carcinogen, and can form during the distilling process. Effective
procedures can be adopted to prevent the accumulation of the precursor in
new distillate, but the way ahead is for the breeding of barley varieties that do
not biosynthesize the precursor. Decanter, which was approved in 2000, is an
example.
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Similar lists for English- and Welsh-, and for Northern Ireland-grown cer-
eals are published by the National Institute of Agricultural Botany (England
and Wales) (NIAB, 2001) and the Department of Agriculture of Northern
Ireland (DANI, 2001). Other countries publish their own lists.
In addition, maltsters normally micromalt small batches of new varieties to
check that they will produce the types of malts required in terms of adequate
levels of diastatic power (DP), a-amylase and fermentable extra ct. Diastatic
power is mainly a measurement of b-amylase activity, but includes some
effects of a-amylase.
In the past 30 years, increasing numbers of barley varieties have become
available to maltsters. Because of their varying degree of suitability for malt-
ing, reliable confirmation of identity is important. The grains of many modern
varieties are so similar in appearance, even under the microscope, that tradi-
tional methods of identification based on morphological features now have a
limited value for barley and are even less useful when applied to malt. In the
1980s the presence of blue aleurone pigment in some varieties (Kym, Atem
and Halcyon) helped in their recognition, but the most useful methods avail-
able at that time were based on electrophoretic separation of storage proteins
extracted from the ker nels (March ylo and Laberge, 1980). Electrophoresis was
followed by the more rapid high-performance liquid chromatography (HPLC)
(Marchylo and Kruger, 1984). More recently, it has become routine to use DNA
fingerprinting (Shewry, 1993). A booklet with detailed descriptions of the
cereal varieties is published annually by NIAB.
Control of barley storage, cleaning and grading
Harvested barley is dried to help its keeping properties. Maximum permissi-
ble moisture contents for short and prolonged storage are quoted as 14.8 per
cent and 13.6 per cent respectively. The ongoing viability of a barley bulk
during storage has been reported (Bamforth and Barclay, 1993) as a function
of its initial viability, storage temperature and moisture content. A numb er of
prediction equations and nomograms are avai lable based on these parameters
(Ellis and Roberts, 1980) – for example, this method indicates that barley with
an initial viability of 98 per cent and moisture content of 12 per cent can be
stored for over a year at 158C without the percentage of viable corns dropping
below 95.
Advances in cereal grain drying are well documented in the technical lit-
erature (Bakker-Arkema et al., 1978; Foster, 1982), and various aspects of grain
drying and storage are described in papers published by the Ministry of
Agriculture, Fisheries and Food (MAFF) and SAC. Tables of equilibrium
humidity are useful in drying calculations, and these are available for barley
(Pixton and Warburton, 1971). Determination of grain moisture content is
carried out before, during and after drying, and the information is used to
monitor and control drying. A range of portable moisture meters is available,
and their operational principle is based on the measurement of conductance,
capacitance and infrared reflectance, all of which are proportional to moisture
content, while specialized balances (where microwave or infrared radiation is
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used to drive off the moisture) are also used. Both meters and balances must
be calibrated against the standard IGB oven method. The stipulated grain
sampling procedure and sample preparation methods must also be used
(IOB, 1997).
Information regarding preventat ive measures against insect infestation and
the treatment of grain storage problems is available in the government pub-
lications referred to above, and lists of approved pesticides are available
(MAFF, 2000). It is essential to choose correct formulations, as otherwise
severe reduction of grain viability can result. It is often specified that barley
procured for the production of malt whisky must be free from pesticide
residues.
The effects of various agronomic practices on grain quality have been dis-
cussed in som e detail (see, for example, Briggs, 1978). Grain damage may not
be obvious in barley received by the maltster, and various methods have been
developed to show injuries arising from fungal infection, mechanical effects of
harvesting, bad drying etc. Tests that indicate the ability of grain to germinate
fully in a rapid and uniform manner are paramount. The most commonly used
tests are described in the IOB Recommended Methods of Analysis (IOB, 1997).
Control of viability
Germinative capacity (GC) is the percentage of living corns that are present in
a sample of grain; the figure is calculated from the percentage of corns that
germinate after immersion for three days in a dilute solution of hydrogen
peroxide (IOB, 1997). A quicker method is to immerse half-corns in a solution
of a tetrazolium salt (triphenyl-tetrazolium trichloride). Visual examination is
carried out after sever al minutes, and kernels with embryos stai ned to an
agreed extent are deemed viable. A disadvantage of this method is that it
can indicate viability in heat-damaged corns that are dead but still have resi-
dual hydrogen peroxidase activity. Germinative energy (GE) is a measure of
the per centage of grains that can be expected to germinate fully if the barle y is
steeped normally a t the time of the test. This test is carried out by germinating
100 corns on filter paper in petri dishes, using 4 ml water.
Control of dormancy
The difference in value between the figures for GC and GE indicates the
degree of dormancy of the barle y under test. In a variation of the GE test,
8 ml of water is used instead of 4 ml. The figure obtained by subtracting the 8-
ml percentage from the 4-ml percentage is known as water sensitivity (WS),
and is generally associated with dormancy. The extent of dorman cy is a var-
ietal characteristic, and is more common after a long, co ol, damp growing
season. It has been reported that high temperatures twelve to sixteen days
after ear emergence promote dormancy, whereas if these occur at the later
mealy stage dormancy is reduced (Reiner and Loch, 1976). When harvesting
conditions are around 20 8C, with barley moistures dropping to 10–14 per cent
in the field, the dormancy period is quite short at around four to six weeks.
Scottish weathe r conditions, with ambient temperatures around 138C, rarely
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lead to barleys with moisture co ntents below 15 per cent in the field, and so
dormancy can sometimes be encountered in susceptible varieties.
Dormancy is a physiological condition that prevents seeds from germinating
when they are presented with an otherwise satisfactory set of environmental
conditions. If barley is required for malting during this period, the dormancy
must be broken by holding the grain at moisture content of 12–13 per cent at
slightly elevated temperatures. This procedure sometimes follows drying. WS
is overcome by introducing air-rests into the steeping schedule.
The phenomenon of dormancy has not yet been fully explained, and a large
technical literature indicate s the ongoing effort that is being made to under-
stand it. Some of the major considerations involve the microflora of the barley
husks, operation of the pentose phosphate pathway during the early stages of
metabolic activity, and the presence of inhibitory levels of endogenous phy-
tohormones such as abscisic acid (Khan, 1977).
As well as occurring as a natural condition dormancy can be induced by
certain dryi ng procedures, and when this happens the GC (peroxide) test can
yield viability figures that are lower than those obtained in the GE tests. To
avoid induced dormancy it is essential to dry barley so that there is always a
free transfer of moisture from the moist kernel when it is subjected to drying
temperatures above ambient.
The germination properties of dried barley have been reviewed by Palmer
and Taylor (1980). Dormancy is less apparent in germination tests carried out
at lower temperatures, and the ratio of GE values determined at 168C and 208C
has been used to distin guish dormant corns from those that have aged during
storage, counts on the latter being unaffected by the temperature reduction
(Bourne and Wheeler, 1985).
Control of pre-germination
Pre-germination is the term used when the corn starts to grow while the barley
is still in the ear. It can occur when a spell of warm, damp weathe r precedes
harvest. Barley containing pre-germinated corns develops unevenly. The
affected corns are susceptible to drying damage and may become reservoi rs
of microbial infection. Barley containing over 5 per cent pre-germinated corns
is unacceptable for malting for Scotch malt whisky.
Screening for pre-germination can be carried out by incubating a sample of
ground barley with Phadebas reagent (dye-linked amylopectin). The presence
of pre-germinated corns as indicated by their a-amylase content can be
detected readily by the producti on of a soluble blue dye (Mathewson and
Pomeranz, 1977).
To determine pre-germination on a percentage basis, a suitable number of
half-corns are incubated in a solution of fluorescein dibutyrate, after which
they are examined under ultraviolet light. Pre-germinated corns possess an
enzyme activity (possibly lip ase) that hydrolyses the non-fluorescent ester to
yield fluorescein, which is easily detectable on the cut surface of the half-corn.
This procedure is simpler than the European Brewery Convention (EBC)
method, in which agar gels are used (Jensen and Heltved, 1982).
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Control of total nitrogen content and corn size, and extract prediction tests
It is a high priority for malt whisky producers that barley procured for this
purpose is of low percentage TN content. The starch content of grain, which
is the main source of fermentable extract, is inversely relate d to its protein
content. The TN content is measured using standard methods, such as
the Kjeldahl and Dumas techniques.
Equipment for analysing large numbers of samples is commercially avail-
able, and variants based, for example, on alkali digestion have been intro-
duced to increase the speed of analysis. Near-infrared reflectance (NIR) is
popular for intake checks, and for these a choice of equipment exists.
Protein content is calculated as TN 6.25. The relative amounts of some
endosperm protein fractions, separated by electr ophoresis, have also been
used to predict the suitability of certain barley varieties for malting
(Wainwright, 1978).
Barley received at intake is usually subjected to a screening test to ascertain
the percentages of corns within various diameter ranges. The procedure
described in An alytica EBC (1975) is used. The barley sample is separated
into fractions of less than 2.8 mm, less than 2.5 mm, less than 2.2 mm and
the screenings, which pass through the 2.2-mm slots.
Thousand corn weight (tcw) is measured using the IOB method. Corn size is
a varietal characteristic, and within a variety it is affected by season and
location. Several malt properties are related to the size of the corn.
Prediction equations that relate potential hot water extract (hwe) to the TN
content of the barley have been used for many years. Early versions involved
additional determinations, such as husk content, and included tcw (Pollock,
1962). All included a ‘varietal constant’, the value of which had to be adjusted
from season to season. Recent equations omit the husk content and tcw but
still contain the varietal constant, which is derived from the results of micro-
malting trials using barleys of different TN content. The use of such predictive
tests has been reviewed by Lloyd (1983).
Peat
Peat is decayed plant material that has formed over thousands of years, and
is generally found in wetland areas. The type of peat formed depends on
the plants involved (such as grasses or heathers) and the location (inland or
maritime), e.g. Scottish mainland, Islay, Orkney.
Peat is used during barley kilning as a flavour source, not as a heat source.
The location at which the peat was obtained, and its method of use, strongly
affects the flavour of the spirit produced. During kilning the peat is burned,
avoiding flaming, to produce a smoke called peat reek. It is burned during the
early stages of kilning, so that the combustion products adsorb to and are
absorbed by the mal t. These effects happen in the range of 15–20 per cent
moisture.**6 Careful control of combustion temperatures is necessary to
achieve the desired degree of peating. Peatiness is caused by a spectrum of
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phenolic compounds, and the amount within the final malt may be up to
80 ppm. The science and technology of using peat is discussed in the following
section.
Malting
Steeping of barley
The science of steeping
The purpose of steeping is to initiate uniform germination and hydrate the
endosperm to a level that is suitable for modification. Steeping conditions
must subsequently a llow satisfactory development of enzymes without
encouraging undue malting losses from respiration and growth.
Grain structure and composition
The detailed anatomy of the barley grain and its chemical composition are
comprehensively described in the brewing literature (Palmer, 1980; Duffus
and Cochrane, 1993).
In a longitudinal section of the barley, two distinctive components of the
corn are apparent; the sm all embryo and the large starchy endosperm (see
Figure 2.1). The scutellum separates the embryo and the endosperm. The
aleurone layer surrounds the endosperm, and the per icarp-testa and husk
enclose the entire kernel. Embryonic axis and scutellum comprise 3 per cent
of the grain dry weight. These tissues are rich in lipids (15 per cent), proteins
44 Whisky: Technology, Production and Marketing
Figure 2.1
Barley grain structure.