since its introduction to North America in the 17th century, barley
has taken on a life of its own. Both two-row and six-row North American
malted barley are rather different from their European cousins and have
developed distinctive new characteristics. Genetics, climate, and breeding
practices have produced a rich variety of malt qualities from which
A brewer's preference
for two- or six-row barley can be born of a number of factors, including
barley and malt purchase prices, quality specifications, and brewing
traditions. Product quality is in turn affected by genetic makeup, environmental
conditions, and the practices of the grower and the maltster.
It is widely believed
that two-row barleys are the best barleys for malting and brewing (1).
In fact, outside North America most of the world's brewing nations exclusively
use two-row barley for malt. Six-row barleys, if produced overseas at
all, are largely used only for feed.
The situation in
North America, however, is rather different and warrants closer examination.
Modern American brewing practices have relied on six-row barleys, partly
because they were better adapted to many regions. In addition, barley
breeding efforts over the past 50 years have reduced, if not obscured,
some of the differences between two- and six-row barleys and malts.
Yet important distinctions remain in terms of kernel size, extract,
protein, and enzyme levels.
preference for two-row barley is based on the fact that two-row barley
yields malts with 1-2% greater theoretical extract, meaning that brewers
can brew more beer. Large-scale brewers, however, must balance the higher
extract yield against the higher cost and lower diastatic power of two-row
malt. Small-scale brewers with less focus on extract yield may find
the differences between the two negligible.
This article delineates
some of the principal differences between North American six- and two-row
malts in the context of historical developments and current production.
Historical Development of
Malting Barley Production
Cultivated barley (Hordeum vulgare) is not native to North America.
English, Dutch, and French traders introduced barley to the eastern
seaboard during the early years of European settlement (2,3). The Spanish
introduced it to Mexico and the American Southwest. The imported English
two-row barley enjoyed adequate growing conditions on the coast, but
as production spread into western New York, six-row barley production
dominated because of the climate. The increasing demand for beer in
new midwestern and western cities continued to draw barley producers
further west, luring them to agricultural lands more favorable to cereal
grain crops. Improvements in the transportation system also helped make
this westward shift possible.
production trends: United States. As of the mid- to late
1800s, U.S. barley production centered in the area now referred to as
the Corn Belt (Iowa, Nebraska, Minnesota, and southern Wisconsin). Disease
and competition from corn and soybean crops, however, led to the eventual
decline of barley in this region, and U.S. production shifted elsewhere.
Today, North Dakota and Minnesota produce the majority of the six-row
malting barley in the United States, with lesser amounts produced in
South Dakota and Idaho. Two-row barley production predominates in Montana,
Idaho, Washington, Colorado, and Wyoming. Both climatic and qualitative
differences contribute to the split.
Canada is now a world leader in malting barley cultivation. Production
has gradually shifted from the East to the prairie provinces of Saskatchewan,
Alberta, and, to a lesser extent, Manitoba. All three provinces grow
both two-row and six-row malting barley cultivars, but two-row production
dominates Canadian crops.
Malting barley production in Mexico is almost exclusively six-row. Most
production occurs in the central states, which are generally in close
proximity to malt houses.
box "Malting Barley Production in North
America" presents more detailed information on barley production
in each country.
vs. Dryland Production and Grain Yields
two- and six-row malting barley varieties produced in Canada and the
United States are spring types (Europe grows both spring and winter
malting barleys). Seeding takes place in the spring, and harvest occurs
from late summer to early fall. Grain yield and hence malt quality are
influenced by many factors from seeding through harvest, including variety
seeded, environment, diseases and pests, soil fertility, and the agronomic
practices of the grower (see Table I).
I: Relative Production Two-Row vs. Six Row*
grain quality parameters for barley produced in the
U.S. (Optimal values)
** Percent retained on a 2.4 X 19.0 mm slotted sieve.
yields in the western United States: The two-row varieties grown
in the western United States realize the greatest yield potential, test
weight, and kernel plumpness relative to all other barley produced in
North America. This advantage comes largely because western barley is
more likely to be irrigated by farmers growing under a contract with
a maltster. Maltsters pay a premium as an incentive for farmers to grow
high-quality malting barley cultivars rather than the better-yielding
feed barley. The farmers can thus afford the costly irrigation. Barley
not grown under contract is often grown under dryland conditions that
limit the plant's growth potential. High daytime temperatures and/or
lack of timely rains during critical periods of crop growth limit the
grain yield and kernel plumpness. Irrigation helps mitigate the effects
of adverse environmental conditions that can reduce the quality of the
grain, thus ensuring a consistent supply of quality two-row malting
Barley in dryland
conditions: Six-row barley yields in the American Midwest are comparable
to dryland yields of two-row barley in the West for many of the same
reasons stated above (climate, irrigation). When western or European
two-row cultivars are grown in the Midwest, they generally yield less
and have fewer plump kernels than adapted six-row varieties. This is
because the western two-row varieties were developed for areas that
may get hot during the day, but that have cool nighttime temperatures
that allow the plants to "recover"; the difference between daytime and
nighttime temperatures is not as great in the Midwest as it is in the
West. The cultivar Triumph developed in Germany, for example, has been
successfully produced in the American West.
in the Midwest also limits the yield of many two-row cultivars. On the
other hand, midwestern six-row cultivars (with a wider range of adaptation)
transplanted to the West have yields comparable to two-row varieties.
Consequently, some midwestern varieties are grown under contract in
the western United States; the contracting of barley in the Midwest,
however, is limited.
is grown almost exclusively under dryland conditions, but these conditions
are not necessarily equivalent to those of the American Midwest; growing
conditions (rainfall, length of season, temperature, and so forth) vary
between, and even within, provinces, allowing the growth of both two-
and six-row barley. Western Canadian yields are, on average, lower than
those for irrigated western U.S. barley.
Only a small amount of Mexican barley is irrigated.
Affecting Barley Quality
programs have minimized the differences between two- and six-row barley,
differences remain in terms of kernel size/uniformity, grain protein
content, and malt enzyme levels (3). Kernel size and protein directly
influence the manner in which six- and two-row barleys are malted by
affecting the rate of water uptake, germination, and modification (see
Tables I and II).
II: Comparitive Analytical Data*
(% dry basis)
(% of the malt, dry basis)
two- and six-row malt quality parameters for barley produced in
the United States. Malt quality data represent approximate averages.
It must be remembered that considerable variation due to changes
in growing conditions, barley quality, or malt processing can occur,
even within the same cultivar. Malt quality data are based on the
methodology of the American Society of Brewing Chemists.
Kernel size and
The central kernel of six-row barleys is symmetrical, but the two lateral
kernels are slightly twisted and also tend to be slightly shorter and
thinner (4). Two-row barley kernels, by contrast, tend to be symmetrical
in shape, more uniform in size, and plumper because only one kernel/rachis
node develops (see
box, "The Anatomy of a Barley Spike"). Because of the irregularities
in kernel size, maltsters often separate each lot of six-row barley
into several kernel size fractions for more uniform germination and
modification. Plumper fractions are reblended upon completion of malting
and used as brewer's malt. The thinner malt kernels may be sold as distiller's
malt, where it is preferred for its high enzymatic activity. The thinnest
barley kernels are removed and sold as feed. Two-row barleys often don't
require such extra handling because their kernel size is more uniform.
A major advance
came in 1961 with the release of the six-row cultivar Larker (5). Larker
significantly reduced the size differential between large kernels in
six- and two-row cultivars. The name Larker, in fact, was coined from
the words "large kernels." Although this variety is no longer used for
malting (having been replaced by newer, improved cultivars), kernel
plumpness in six-row cultivars released since that time has generally
continued to increase. Nevertheless, the plumpness of two-row cultivars
still tends to be greater, particularly when grown under irrigation
in adapted environments.
serves as a moderate indicator of malt extract yield (3). Plumper kernels
are thought to have a higher starch content, which is the principal
contributor to extract. Before the breeding breakthroughs of the 1970s,
the extract from six-row malts was as much as 4% below those of two-row
malts. The release of the cultivar Morex (so-named because it has "more
extract") in 1978 marked a trend toward higher extract levels for six-row
barley (5). Currently, six-row malts are only 1-2% lower.
Another important distinction between six- and two-row barley cultivars
is in the average level of grain protein (3). A high protein level often
indicates a thinner kernel with less starch available for conversion
to malt extract. Acceptable six-row malting barleys may range from 12
to 13.5% protein, whereas two-row cultivars range from 11 to 13%; barleys
with greater than 13.5% protein are rarely used for malt. The high temperatures
and moisture stress frequently encountered in dryland conditions (under
which most six-row barley is grown) can limit the amount of grain fill
(starch synthesis) and thus result in higher protein contents.
The protein content
differential is also related to genetic differences in how each cultivar
accumulates protein during grain development. Total protein content
is defined as nitrogen content x 6.25. Because the net loss of nitrogen
during malting is minimal, the total protein content does not change
greatly in the process. Much of the barley protein, however, is converted
into a soluble form by proteolytic enzymes; a portion of this is further
broken down into amino acids and peptides in the wort.
Six-row malts tend
to yield higher levels of wort-soluble protein. The ratio of soluble
protein to total protein is an indication of the extent of protein breakdown
(modification) during malting: 40-45% is considered acceptable.
Higher protein malting
barleys are generally believed to inversely reduce the level of malt
extract in the kernel. In addition, high protein content can lengthen
steeping time, cause erratic germination (especially if grain traders
blend low- and high-protein barleys to meet protein limits), increase
malting losses, and increase enzymatic activity and, ultimately, the
level of dimethyl sulfide. High soluble protein levels can sometimes
result in brewing or beer-quality problems.
time: While most six-row barley cultivars require four-and-a-half
to five days of germination to achieve proper malt modification, traditional
North American two-row cultivars generally require an additional one
to two days of germination time (3). Harrington, however, a two-row
cultivar released in 1981, modifies in only four days. Because Harrington
is currently the predominant two-row cultivar in North America, particularly
in Canada, it can safely be stated that modern two-row barleys generally
require less malting time than six-row barleys -- a testimony to the
success of modern breeding programs. This advantage represents a major
economic consideration for maltsters. This change of tendency for two-row
cultivars has represented a major advancement achieved through barley
Six-row malts traditionally (that is, before recent breeding advances)
yielded higher levels of the desirable starch-degrading enzymes a-amylases
and greater diastatic power (DP). a-amylases are the enzymes
that convert starch to dextrins, reduce mash or cooker viscosity, and
increase the susceptibility of starch to ß-amylase attack (7,8).
DP is a measure of the activity of the malt enzymes that break down
complex carbohydrates into reducing sugars (principally ß-amylase,
the key saccharifying enzyme responsible for converting starch to fermentable
maltose and for further breaking down large dextrins). The modern two-row
cultivar Harrington, however, has levels of a-amylases equal
to or slightly greater than those of current six-row malting cultivars.
Despite the recent advances in favor of more a-amylases, two-row
malts continue to have considerably lower levels of DP -- a potentially
limiting factor in some applications, such as when high levels of unmalted
grains are used as adjuncts.
The ß-glucan content of most barley cultivars falls between 4
and 7% of the total grain weight (9). In general, the ß-glucan
content of six-row barleys is slightly lower than that of two-row barleys.
ß-glucans are usually extensively degraded by malt ß-glucanase
enzymes during germination, meaning that little will be extracted into
wort. Undegraded ß-glucans contribute to viscosity and can cause
wort separation and beer filtration problems (10). Both two- and six-row
North American malts tend to be well modified; ß-glucan-related
problems are not often encountered but are more likely when undermodified
malt or high levels of umalted barley are used.
Husk content provides one other difference between two- and six-row
barley. A thin, tightly adhering husk is desirable in all malting cultivars
because the husk protects the germinating grain during malting and plays
an important role in lautering. Six-row barleys are generally believed
to have a higher husk content because they tend toward thinner kernels,
but husk content varies with growth environment (11). High husk content
barley can mean more phenolics end up in the wort, thereby contributing
an astringent flavor to beer. Oxidizable polyphenolic substances react
with proteins and may contribute to haze formation (8). Care must be
taken in the brewing process to avoid extraction of these compounds
from the husk and to promote their precipitation in the wort (the hot
for Brewing Practice
Protein and DP:
In terms of brewing performance, the most apparent differences between
two-and six-row malts relate to their levels of grain protein and diastatic
power. The higher protein and enzyme levels of adapted six-row cultivars
allow for the widespread use of cereal adjuncts in major North American
breweries and the double-mash* system for precooking them (4).
mash system is used with rice or corn grits. A portion of the malt
bill can be replaced (usually no more than 40%) with rice or corn.
The rice or corn grits are first "cooked" with a small portion of
the malt in a separate vessel known as a cereal cooker. Most of
the malt will be mashed in the main mash vessel. As the temperature
rises in the cereal cooker, the adjunct starch is gelatinized, which
makes it susceptible to enzymatic hydrolysis by the amylases contained
in the malt. Eventually, the cooker temperature will reach boiling,
after which the cereal mash is transferred to the main mash tun.
This transfer usually occurs at the end of the main mash protein
rest and raises the main mash temperature to saccharification temperature.
size: The more uniform kernel size distribution of two-row malt
helps brewers, at least those using two-roller mills, obtain a proper
grind at the beginning of the brewing process (12). Kernel size differences,
however, are likely to be less significant when using more sophisticated
six-roller mills with screening systems, such as those used by the major
breweries. In terms of the type of wort separation method used, a larger
grist particle size distribution is extremely important in lautering,
and virtually unimportant with the modern mash filters used by some
large-scale brewers. Mash filters are able to handle smaller particles
because they use filter cloth, a lower bed depth, and higher pressures.
Two-row barley yields malts with 1-2% greater theoretical extract (13).
Extract is a major economic concern for many large-scale brewers because
the amount of brewhouse extract obtained determines the amount of beer
that can be produced from a given amount of malt. Small-scale brewers,
however, are generally less concerned about extract yield and may not
consider this as important a criterion in their malt choice. Large-scale
brewers must weigh the higher extract levels of two-row malts against
higher cost and often lower diastatic power.
During the malting and brewing processes, approximately 38-45% of the
malt protein is converted to wort-soluble protein in the form of various
nitrogenous substances, including peptides and amino acids (3,7,8,13).
The balance of these components in the wort is important because they
contribute to beer foam and mouthfeel, beer color and flavor, and yeast
Some soluble protein
is essential. Problems can arise, however, when levels become excessive
in wort or beer. This level depends on the process and product, but
problems might be expected when wort-soluble protein exceeds 5.5%. High
levels of protein, like those found in six-row malts, can lead to too
much color development during wort boiling, filtration problems, and
the risk of haze formation.
adjuncts. The widespread use of unmalted cereal adjuncts (corn,
rice, etc.) by North American brewers developed, in part, to compensate
for the higher soluble protein levels of six-row malts and, later, because
adjuncts are cheaper. It is generally accepted that 150-170 ppm amino
nitrogen (component of soluble protein) is required in the wort to support
adequate yeast metabolism and fermentation (12). A high-protein six-row
malt will provide levels far in excess of these values. Because the
protein in corn or rice adjuncts is largely insoluble, it is possible
to replace a portion of the malt with adjunct and thus dilute the overall
level of wort-soluble nitrogen. Cereal adjuncts can be used to replace
up to 40% of six-row malt grist without adversely affecting fermentation
performance. Two-row malt typically allows for less adjunct use because
of its lower soluble nitrogen levels and lower diastatic power.
The use of cereal
adjuncts began as an innovative response to available malt quality and
was born of concern for quality. Now, with improved North American malt
strains available, it is no longer necessary but is now both economically
advantageous and traditional for those breweries' beers.
DMS. Protein levels also increase the potential for dimethyl sulphide
(DMS) formation in beer. The precursor of DMS, S-methyl methionine (SMM),
is formed through protein breakdown during malting (14,15). Much of
the SMM is converted to DMS through thermal decomposition during kilning
and wort boiling. DMS formed during kilning and wort boiling is lost
to the atmosphere. Pale malts generally have higher levels of SMM than
do darker, highly kilned malts. When the length or vigor of boiling
is inadequate to convert all residual SMM, DMS may continue to form
as the wort cools. This DMS may persist into the beer. Although some
DMS is desirable in lager beers, levels in excess of 50 ppb are thought
to contribute a cooked or sweet corn flavor. Six-row malts contain higher
levels of the DMS precursor SMM, presumably because of their higher
Higher protein levels are somewhat positively correlated with malt enzyme
levels and six-row cultivars tend to have higher levels of DP than do
two-row cultivars (3,14). Levels of a-amylase are roughly equal.
Because the ratio
of DP to a-amylase is greater in six-row malts, one might expect
conversion to fermentable sugars to proceed more rapidly. This may be
of importance when throughput (brews/day) is a concern. For the home
brewer, it may provide some leeway when high mash-in temperatures are
used because more conversion would take place. ß-amylase, the
major component of DP, is much more temperature-sensitive than a-amylase
and is inactivated earlier in the mash.
Although the higher level of DP in six-row malts also allows brewers
to use more cereal adjuncts (see "Proteins and adjuncts," above), the
situation with syrup adjuncts is somewhat different. Syrups are prepared
through the enzymatic hydrolysis of corn starch to fermentable sugars.
Because this adjunct is added in a fermentable form, excess malt enzyme
is not needed for fermentation. In fact, some brewers have reported
problems with the high enzyme and soluble protein levels of certain
modern six-row cultivars.
World of Choices
distinguish two- and six-row malt, but these differences have become
less pronounced over the past 20 years as new varieties have been bred.
The high protein and enzyme content of six-row barley makes it unlikely
that a brewer producing an all-malt beer would wish to use exclusively
six-row malt. Supplementing two-row malt with some six-row malt, however,
might serve to increase extraction, conversion time, and fermentability,
especially with high proportions of adjunct. Although most craft brewers
don't normally use corn and rice, other unmalted grains such as wheat,
barley, and oats are becoming increasingly common.
On a final note,
it should be mentioned that every barley cultivar, whether six-row or
two-row, can have distinct effects on the organoleptic (flavor, aroma,
color) characteristics of beer (3). Two-row malts are generally believed
to yield a mellower flavor, but these differences are very difficult
to quantify. Malting barley and malt are marketed on the basis of cultivar,
and, thanks to modern breeding practices, brewers have a world of options
when choosing which cultivar best meets their processing and beer quality
The authors thank
Sherman Chan, Scott Heisel, John Holt, Norman Kendall, Mauro Zamora
Diaz, John Mittleider, and William Wilson for their valuable input.
Statistics on barley production in Canada and the United States were
from reports provided by the American Malting Barley Association (Milwaukee,
Wisconsin) and the Brewing and Malting Barley Research Institute (Winnipeg,
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is an associate professor of Cereal Science at North Dakota State University,
where he specializes in research on the biochemistry of barley and malt
quality. He is a member of the American Society of Brewing Chemists,
the Master Brewers Association of the Americas, the American Chemical
Society, and the American Association of Cereal Chemists.
Horsley is an associate professor of Plant Science at North Dakota State
University. He is a barley breeder and specializes in research on the
genetics of malt quality and disease resistance. He is a member of the
American Society of Agronomy and the Crop Science Society of the Americas.