From field barley to malt: Detection and specification of microbial activity for quality aspects

Barley grain carries a numerous, variable, and complex microbial population that mainly consists of bacteria, yeasts, and filamentous fungi and that c an partly be detected and quantified using plating methods and microscopic and molecular techniques. The extent and the activity of this microflora ar e determined by the altering state of the grain and the environmental condi tions in the malt production chain. Three ecological systems can be disting uished: the growing cereal in the field, the dry barley grain under storage , and the germinating barley kernel during actual malting. Microorganisms i nteract with the malting process both by their presence and by their metabo lic activity. In this respect, interference with the oxygen uptake by the b arley grain and secretion of enzymes, hormones, toxins, and acids that may affect the plant physiological processes have been studied. As a result of the interaction, microorganisms can cause important losses and influence ma lt quality as measured by brewhouse performance and beer quality. Of partic ular concern is the occurrence of mycotoxins that may affect the safety of malt. The development of the microflora during malt production can to a cer tain extent be controlled by the selection of appropriate process condition s. Physical and chemical treatments to inactivate the microbial population on the barley grain are suggested. Recent developments, however, aim to con trol the microbial activity during malt production by promoting the growth of desirable microbial cultures, selected either as biocontrol agents inhib iting mycotoxin-producing molds or as starter cultures actively contributin g to malt modification. Such techniques may offer natural opportunities to improve the quality and safety of malt.