Fungal Contamination of Barley and Malt
Technical University of Munich, TUM School of Life Sciences Weihenstephan, Chair for Technical Microbiology, Freising, Germany
Fungal contamination of barley and malt results in a high economic burden from malt yield loss, quality failure, and costs connected to the presence of toxic fungal secondary metabolites, i.e. mycotoxins. This chapter describes the routes and factors that influence fungal contamination of cereals and malt, both qualitatively and quantitatively, as well as the consequences which fungal growth may have in terms of malt and beer quality. Focus is given to the role of mycotoxins and their fate during malting and brewing as well as to recent research in the field of beer gushing. Since analysis is a strong tool to prevent fungi and their metabolites from entering the malt-beer chain, recent developments in the analytical toolbox are discussed, including chemical and molecular biology-based approaches. Finally, possible ways for the prevention of fungal growth in the field and during malting are discussed.
Fungal contamination of agricultural commodities results in worldwide economic burden from yield loss, quality failure, and costs connected to the presence of toxic fungal secondary metabolites, i.e. mycotoxins. Some rough calculations may help to illustrate the magnitude of the problems induced by fungal contamination of barley and it can be concluded that they may be transferable to other crops such as wheat and sorghum as crops of minor worldwide importance for the brewing industry. Based on data from 17 different regions of the world for the period 1996-1998, Oerke and Dehne (2004) estimated loss potentials due to four different pest groups (weeds, animal pests, fungal and bacterial pathogens, viruses) for major crops such as wheat, rice, maize, barley, potatoes, soybeans, sugar beet and cotton. They estimated loss potential to be about 50% for barley with actual losses of up to 26-30% occurring under unfavourable conditions. Of the actual losses, about 15% are accounted for by fungal and bacterial pathogens with no information given about the proportion of fungal pathogens in this estimate. We would tend to give it a 50% share in this calculation. According to the UN Food and Agricultural Organization, (FAO, 2009) barley is the second most important coarse grain crop with a worldwide production of 136 million metric tons in 2007 harvested on 56.6 million hectares of acreage. Taking the above figures into consideration, an estimated loss of 10.2 million metric tons in worldwide barley production may occur due to fungal pathogens. Based on an average price of 180 $US per metric ton (feed/malt barley), this amounts to a worldwide annual loss of $1.8 billion (US) in agribusiness. Of the 136 million metric tons ofbarley harvested in 2007, an estimated 21.36 million metric tons of malt have been produced (FAO, 2009) meaning a raw material consumption of approximately 27 million metric tons of screened barley (conversion factor from raw material to malt 1.267). Thus there is a total world production of approximately 30 million metric tons of malting barley or $6.2 billion of turnover in global agribusiness.
The FAO have previously published a 25% estimate for the proportion of total food supply contaminated by the major mycotoxins in precariously high concentrations (Mannon and Johnson, 1985). Given the fact that this estimate is also true for malting barley, five million metric tons of that commodity can be supposed to be either unfit for processing in the malt house and have to go to alternative uses (with reduction in producer benefit) or can be sold only to the malt producer at a reduced price, both measures adding up to further losses. Costs for mycotoxin management can only be roughly estimated since they are influenced by several different cost factors such as research, testing, detoxification, discarding, health costs and insurance. For the situation in the USA, Vardon (2003) estimated an annual range of cumulated losses from $0.5 million to over $1.5 billion only from the major mycotoxins aflatoxin (maize and peanuts), fumonisin (maize, wheat, barley), and deoxyniva- lenol (DON) (wheat, barley). Uncertainties were built into the cost model based on commodity outputs, prices, and contamination levels based on surveillance samples and compliance with FDA regulatory limits.
Wheat and barley scab (head blight) induced by Fusarium graminearum and F. culmorum is an excellent example of the high economic and social impact of fungal contamination of cereals. According to Windels (2000), the losses in the United States agricultural production of wheat and barley caused by several severe outbreaks of the disease in the 1990s and early 2000s were estimated to be close to $3 billion including losses of $400 million in barley production. Costs were due to reduction both of yield and quality and led to a considerable change both in agricultural practice and cropping systems and also in the social structure of rural communities in affected regions due to farm exits and depopulation. As a consequence, malt producers and breweries suffered from problems with mycotoxins (DON, fumonisin) and gushing due to fungal contamination as well as from a shortage in barley supply which had to be compensated for by import of (more expensive) raw materials.
However, fungal contamination of brewing cereals means more than the potential contamination of commodities with mycotoxins. Fungi influence the quality of barley, wheat and sorghum and the malts produced from them by altering their composition and structure thereby influencing parameters such as malt colour, wort filterability, fermentation performance, beer colour and aroma. They may influence the brewing process by interfering with the metabolism of the barley grain during malting or with the yeast metabolism during brewing. They often leave tiny amounts of highly potent proteins causing the gushing of beer.
Current research on the taxonomy, physiology, and toxicology of barley- and malt-related fungi has provided a deeper insight into the way these organisms interact with their environment and how this interaction influences the quality of brewing malt and beer. Results from this research may help to cope with some of the problems related to fungal contamination of brewing raw materials and thus help to find solutions to the benefit of the brewing industry.
The following chapter provides an overview of published research about the influences fungal organisms have on barley and malt and how they interfere with the brewing process and with the final product. Moreover, the following chapter will discuss gaps in our knowledge regarding fungal contamination of barley and malt as well as its management.