| How Healthy
Is Your Malt? -
What You Should Know about a Disease that Could Affect Your Beer
by Neil Gudmestad, Raymond Taylor and Paul Schwarz
Although the grain disease called Fusarium head blight has
posed little serious threat to the North American brewing industry in
the recent past, reports of the disease's recent resurgence in certain
regions may merit some concern among growers, maltsters, and brewers
Any crop is potentially
susceptible to the ravages of pests or disease, and barley is no exception.
One fungal disease has been appearing in certain production areas where
climate and soil conditions are conducive to the fungus's growth. The
disease, known as Fusarium head blight (FHB, or scab), affects
barley and wheat and has created many problems for farmers and livestock.
This article presents what we know and don't know about the disease's
effect on the malting and brewing industries.
We Should Worry about It
The Fusarium fungus itself can diminish grain quality and make
swine and other livestock ill. The economic pain that farmers feel from
production losses may well be passed on to end users. But the fungus
is only the beginning of the trail of hazards wrought in fields infected
with Fusarium. The fungus produces resilient toxic by-products
that are able to survive the malting and kilning process and creep into
the finished beer.
Studies have shown
that high doses of these toxins can be lethal to laboratory animals,
although the threat to humans from the typically low levels that might
be found in beer and other cereal food products has yet to be clearly
established. Even in the absence of a clearly defined health threat,
however, brewers may wish to consider public perceptions about health
and quality when they select their malt. In addition, the disease is
linked to certain brewing-related problems, including gushing in packaged
beer. For these reasons, it well worth examining and understanding FHB.
FHB is most common among grain crops in the humid and semihumid production
areas of the world, where the climate is favorable to fungus development.
Because of the disease's dependence on warm, moist weather, its occurrence
and severity vary greatly from year to year. FHB has been known to strike
with considerable magnitude in some of the barley production areas of
North America, Europe, China, Korea, and Japan.
FHB is not a new
disease; it was recorded as early as 1890, when Indiana wheat crops
were reportedly infected with severe scab. Scab of barley hit the eastern
and central U.S. corn belt so hard during the first half of this century
that it essentially eliminated barley production (1,2). More recently,
FHB epidemics erupted in German crops in 1987 and 1991 (3). In North
America, the fungus has hit the Midwest the hardest. The disease has
been widespread enough to have an economic impact on the wheat and barley
industry in the midwestern United States and central Canada (Manitoba)
Of concern to brewers
buying malt, then, is the six-row barley typically grown in the Midwest
and all European barley and wheat (midwestern wheat is not typically
used for malting).
Unfortunately, the options for controlling Fusarium-related problems
are currently limited as long as weather patterns and modern minimum-tillage
practices continue to give Fusarium the perfect environment to
grow and spread (see box, "The
Root of the Problem"). All current barley varieties are highly susceptible
to FHB. American barley growers typically disdain the use of fungicides
because of their poor efficacy and high cost.
Maltsters are limited
in their options for control. Gravity separation can be effective for
removing infected wheat kernels, but cleaning is not an effective tool
for barley, neither technologically nor economically. DON levels in
barley can be reduced only 10-20% by cleaning, if at all.
of Fusarium during the malting process is not really an option
either because of concerns over residues and reduced malt quality. Biologically
controlling Fusarium in the malthouse by inoculating the barley
with other microorganisms (yeasts and bacteria, for example) has shown
some promise in European studies (4). But the most common means of control
is simply to avoid using infected barley. Most maltsters and large breweries
in North America routinely screen for FHB and/or the mycotoxins it produces
and accept only barley or malt with undetectable to minimal levels of
on Barley and Animals
blight rears its ugly head in several ways. Infected grain may develop
floret sterility or produce light, shriveled kernels. Visual signs of
infection are not always apparent, however, particularly on barley. A
salmon-pink to reddish dustlike growth may be evident on heavily infected
kernels or spikelets. Developing kernels are often shrunken and grayish
brown. Wheat kernels are particularly susceptible to infection, where
FHB manifests in extremely shriveled berries called "tombstones," which
are discarded during harvesting or the grain-cleaning process.
In addition to grain
quality degradation, toxins produced by the fungus can cause illness in
many animals, particularly swine. One compound in particular, deoxynivalenol
(DON, sometimes referred to as vomitoxin), is the most common mycotoxin
associated with small-grain production in North America (5) and the most
common toxin occurring on barley in the upper midwestern United States
(6). Interestingly, DON can be detected in seemingly healthy kernels that
lack obvious FHB symptoms.
Head Blight at a Glance
- FHB is
a worldwide fungal disease of cereal crops, including barley
and wheat. Epidemics have been reported in Europe, Asia, and,
most recently, in North America.
- FHB infection
can result in inferior grain quality and mycotoxin contamination.
- DON (deoxynivalenol)
is the most common mycotoxin on grains in North America.
- DON causes
feeding problems in animals, particularly swine. Because vomiting
or feed refusal (aversion) may be encountered at high levels,
the compound is also known as vomitoxin.
- The effects
of chronic exposure to DON on human health are not known.
- FHB infection
of barley and the DON it produces can result in reduced malt
quality and problems in malting and brewing, including gushing
in packaged beer.
- Many maltsters
and brewers routinely test for the presence of the fungus or
Fusarium is killed during kilning, DON can survive into the
surveys have shown minimal incidence of DON in commercial beers.
The effect of DON
toxicosis on humans is not yet clear from research. DON is comparably
less toxic than some of the other compounds produced by Fusarium
that can have harsher effects on livestock, but DON nonetheless can
cause problems by prompting livestock to either refuse to eat or, at
higher levels, to vomit (thus the toxin's common name). The accompanying
box, "The Root of the Problem," tells more about the mycotoxins produced
by Fusarium and their effects on livestock.
on Malt and Finished Beer
As previously mentioned, the problem for brewers is that the Fusarium
fungus thrives on the conditions inherent in the malting process. While
the fungus itself is killed during kilning, the heat-resistant mycotoxins
can persist into the finished beer.
The transfer of
a mycotoxin from its barley host into the beer is largely dependent
upon the solubility and temperature stability of the specific toxin.
One study using naturally infected barley to evaluate the fate of DON
during the malting and brewing process (7) resulted in the following
In the malthouse:
The DON mycotoxin is water soluble and is rinsed from infected barley
during steeping. In the first phase of malting, barley is steeped in
water until it reaches about 45% moisture. In modern practice, steeping
actually involves a number of cycles of water immersion followed by
drain or air-rest stages.
present on infected grain, however, persists through steeping. Thus,
although infected barley is typically free of DON at steep-out, the
subsequent four- to five-day germination stage provides ideal temperature
and relative humidity for further fungus growth and therefore further
Kilning then kills
the Fusarium, halting further toxin production. The amount of
DON produced during the malting of infected grain is highly variable,
and probably depends on the individual sample as well as on malting
conditions. In most samples of malted barley analyzed in the study (7),
DON levels in malt were lower than in the original infected barley.
In the finished
beer: Only small amounts of DON present on the malt are later detected
on the spent grains; most of the DON (80-95%) is extracted during mashing.
Because of its high temperature tolerance, DON will persist through
the boil and into the finished beer. One must keep in mind, however,
that even though much DON is extracted, it will undergo an approximate
8- to 10-fold dilution during brewing.
In a survey (10)
of six studies on mycotoxin contamination in beers worldwide (the studies
covered 327 commercial beers from the United States, Canada, and Europe),
DON was typically absent from the beers analyzed, suggesting that either
FHB was not present at all in the malt or that the malting industry
was effective in its screening for the disease. The highest level of
DON reported was 570 parts per billion (ppb) in a German wheat beer;
that beer, however, was part of a study on gushing beer, and was therefore
not randomly selected. Most beers that tested positive in random testing
had much lower levels, on average 5-20 ppb, if detected at all.
At these low levels,
DON probably presents no concern for acute toxic reaction. An individual
would need to consume several hundred liters of beer in one sitting
to accumulate a lethal dose of DON. The FDA's advisory level is a maximum
of 1 ppm in wheat products for human consumption, or 1,000 ppb (11);
no advisory levels have yet been set for malting barley. The effects
of low-level chronic exposure (long-term exposure) are not yet known.
Whatever the facts
turn out to be, craft brewers rely heavily on the public's perception
of the purity of their products, and public concern may well be exacerbated
by DON's common name, vomitoxin.
Effects on brewing: Possible health concerns are just part of
the picture. The malting and brewing performance of barley or wheat
also may be affected by Fusarium. All of the effects of FHB/DON
infection on grain metabolism are not yet known, but one study reported
malt quality losses and increased extract, alpha-amylase, and wort nitrogen
when barley samples were artificially infected with Fusarium
during malting (12). These observations make sense based on what we
do know. DON acts as an inhibitor of protein synthesis, so it can potentially
affect germination and other metabolic processes in the germinating
grain. The Fusarium fungus itself produces amylolytic and proteolytic
enzymes and also gibberellins, which promote enzyme synthesis in the
barley. Excessive enzyme activity can make conversion difficult to control.
Fermentation: When applied to wort, DON has been reported to
retard yeast growth and attenuation (13), but the concentration required
for this effect (50 ppm in wort) would mean an initial malt contamination
of several hundred ppm, which is not likely to be encountered. Further
studies are needed to evaluate the effects of lower levels of wort DON
(<100 ppb) on fermentation before realistic conclusions can be drawn.
Off-flavors: Molds such as Fusarium are known to produce
off-flavors in beers -- one reason that brewers have long avoided moldy
barley even before anything was known about mycotoxins.
Gushing: Perhaps the best known effect of FHB on malting and
brewing quality is the propensity of Fusarium-infected malts
to cause gushing problems in packaged beer. Gushing has been defined
in the following way: "Immediately after opening the bottle, that is,
by removing the excess pressure above the beer, a very great number
of fine bubbles are formed throughout the volume of beer and ascend
very quickly, creating foam which flows out of the bottle or, in severe
cases, actually spurts from the bottle. Usually, the violent action
ceases after a few seconds" (14).
The type of gushing associated with the use of fungus-infected barley
is referred to as primary gushing, and although most commonly
associated with Fusarium, it can also be caused by other fungi
such as Aspergillus, Rhizopus, Penicillium, and Nigrospora. The
actual compound (or compounds) that cause gushing is unknown, but research
has suggested that it may be composed of protein (15) that provides
additional nucleation sites on which carbon dioxide bubbles form. Its
exact nature eludes determination; few people have conducted long-term
research, and the activity is difficult to isolate. What is known is
that this compound appears to increase with the level of Fusarium
on barley and malt, and the amount of gushing observed would thus appear
to increase with the severity of the Fusarium infection on malt
(16). Little or no overfoaming is observed when infection levels are
low to nil, whereas one-half or more of the bottle contents may erupt
when the malt has been heavily infected.
in action: This beer was prepared in a laboratory trial from a malt
sample that was heavily infected with Fusarium. A compound produced
by the Fusarium fungus has been found to cause such gushing, though
the effect can also be caused by other brewing and packaging process
Not all gushing, of course, is necessarily related to fungal infection.
Secondary gushing may be caused by a number of processing factors.
Assuming the malt presents no visible signs of infection, brewers should
rule out the following possible problems before suspecting FHB: contamination
of packaging material with foreign particulate matter, rough bottle
surface, overcarbonation, calcium oxalate crystals (otherwise known
as beerstone, problems may occur when it precipitates in the finished
beer), hop oxidation products, excessive haze, and filtration breakthroughs.
A few other possibilities exist as well (14). One possible clue is that
gushing problems due to process factors might be expected to affect
bottles in a batch of beer sporadically, whereas FHB infection would,
of course, affect an entire batch of beer.
What you can do in the brewery: As mentioned before, visual
signs of infection are unfortunately not necessarily apparent in barley,
though heavily infected barley may well result in discolored and/or
malformed malt. Although black lights are effective for aflatoxin detection,
they do not work for Fusarium and DON. Test kits of varying accuracy
and price are available for conducting your own malt analyses, and some
testing services will evaluate both malt and beer for toxins (see the
"For More Information" section). Asking the right questions of your
malt supplier may be your best line of defense.
Implications for Growers, Maltsters, and Brewers The rigid standards
set by large U.S. breweries and maltsters have helped to lessen the
impact of this problem over the years, but any increase in the extent
of infected crops raises the potential number of lot rejections. This
could adversely affect the grower as well as the malting company; if
the grain becomes highly contaminated it may not even meet livestock
feed requirements, resulting in a financial loss for farmers and a grain
deficit that might raise the price of subsequent crops. The economic
effects may be felt all the way down the line.
Because the Fusarium problem has primarily affected the regions
of the United States and Canada producing six-row barley, brewers who
exclusively use U.S. or Canadian two-row malt may be able to breathe
a bit more easily. But brewers purchasing malt from Europe, where conditions
for disease development in barley and wheat producing areas are more
commonly found than in the United States, may wish to exercise some
caution. The fact that an extremely high level of DON was measured in
a German wheat beer should not be ignored.
The full effect that beer prepared from barley infected with FHB could
have on brewers and consumers may not be known for some time, but public
perceptions alone could be enough to cause concern in the industry.
This article is intended to help educate brewers about the facts of
Fusarium infection. By asking the right questions and knowing
what to watch for, anyone purchasing malt can decrease the chance of
using diseased malt.
For More Information
Much cooperative research is being conducted by government and industry
groups. The Canadian Grain Commission maintains a website with up-to-date
information on FHB, including maps, photographs, and available publications
(www.cgc.ca). The United States does
not yet have a central repository for information on the disease. Some
information can be found, however, at http://www.rrtrade.org/smallgrains/research/research.htm,
and a search will find some other scattered information sources as well.
The references cited in this article do, however, embody an excellent
survey of the available literature. DON test kits are available from
several sources, including the companies named in the "Products and
Services" section of this publication (see "Malt Testing Kits," p. 159).
Many companies also offer malt testing services; some may also be able
to test finished beer for DON infection. Dr. Howard Caspar of North
Dakota State University, for one, will test commercial malt or beer
samples for a fee (tel. 701/231-7529), and the Canadian Grain Commission
also offers a testing service (tel. 204/983-2770).
- G. Bai and G.
Shaner, "Scab of Wheat: Prospects for Control," Plant Disease
78, pp. 760-766 (1994).
- D.E. Mathre,
Ed., "Scab or Head Blight," in American Phytopathological Society
Compendium of Barley Diseases (APS Press, St. Paul, Minnesota,
1982), pp. 42-43.
- L. Niessen, M.
Böhm-Schrami, H. Vogel, and S. Donhauser, "Deoxynivalenol in Commercial
Beer -- Screening for Toxin with an Indirect Competitive ELISA," Mycotoxin
Research 9, pp. 99-109 (1993).
- A. Haikara, H.
Uljas, and A. Suurnëkki, "Lactic Starter Cultures in Malting -- A
Novel Solution to Gushing Problems," in European Brewery Convention,
Proceedings: #24 (IRL Press Ltd., Oxford, UK), pp. 164-172.
- T. Tanaka, A.
Hasegawa, S. Yamamoto, U.S. Lee, Y. Sugiura, and Y. Ueno, "Worldwide
Contamination of Cereals by the Fusarium Mycotoxins Nivalenol, Deoxynivalenol,
and Zearalenone," Journal of Agricultural and Food Chemistry
36, pp. 979-983 (1988).
- P.B. Schwarz,
H.H. Casper, and J.M. Barr, "Survey of the Natural Occurrence of Deoxynivalenol
(Vomitoxin) in Barley Grown in Minnesota, North Dakota and South Dakota
During 1993," Master Brewers Association of America Technical Quarterly
32 (4), pp. 190-194 (1995).
- P.B. Schwarz,
H.H. Casper, and S. Beattie, "Fate and Development of Naturally Occurring
Fusarium Mycotoxins During Malting and Brewing," Journal of the
American Society of Brewing Chemists 53 (3), pp. 121-127
- C.J. Mirocha,
S.V. Pathre, and C.M. Christensen, "Mycotoxins," in Advances in
Cereal Science (American Association of Cereal Chemists, St. Paul,
Minnesota, 1980), pp. 159-225.
- Vicam, company
brochure (Vicam, Watertown, Massachusetts).
- P.M. Scott, "Mycotoxins
Transmitted into Beer from Contaminated Grains During Brewing," Journal
of the Association of Official Analytical Chemists International
79, pp. 875-882 (1996).
- U.S. Department
of Agriculture, Program Bulletin 96.2, "Deoxynivalenol (DON)
Advisory Levels," USDA, Grain Inspection, Packers, and Stockyards
Administration, Federal Grain Inspection Service (15 February 1996).
- W. Sloey and
N. Prentice, "Effects of Fusarium Isolates Applied During Malting
on Properties of Malt," in American Society of Brewing Chemists,
Proceedings: 1962 (American Society of Brewing Chemists, St. Paul,
Minnesota, 1962), pp. 24-28.
- R. Ryman, "The
Effect of Natural Contamination of Grain by Fusarium and Associated
Mycotoxins in Malting and Brewing," malting science thesis (Heriot-Watt
University, Edinburgh, Scotland, 1994).
- G.P. Casey, "Examination
of Mechanistic Differences Between Primary and Secondary Gushing and
Assay Procedures Used to Assess Malt/Beer Gushing Potential," Master
Brewers Association of America Technical Quarterly 33 (4),
- K. Kitabatake,
S. Fukushima, I. Kawasaki, and M. Amaha, "Gushing-Inducing Peptides
in Beer Produced by Penicillium Chrysogenum," in Peptide Chemistry,
H. Yonehara, ed. (Protein Research Foundation, Osaka, Japan, 1979),
- P.B. Schwarz,
S. Beattie, and H.H. Casper, "Relationship Between Fusarium Infestation
of Barley and the Gushing Potential of Malt," Journal of the Institute
of Brewing 102, pp. 93-96 (1996).
Neil Gudmestad is professor of plant pathology at North Dakota State University (NDSU) in Fargo. He has been interested in barley since the mid- to late-1970s when he first worked on barley diseases. His most recent interest in the plant centers on his hobby of home brewing.
Raymond Taylor is head brewer at the Great Northern Restaurant & Brewery in Fargo, North Dakota. His interest in barley diseases arises from his formal training in the Department of Plant Pathology at NDSU as well as his current job and home brewing hobby.
Paul Schwarz is associate professor in the Department of Cereal Science at NDSU, where he specializes in research on the biochemistry and use of barley and malt.