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Genetically modified brewer's yeast encoding a-acetolactate decarboxylase (a-ALDC) was tested in immobilized yeast bioreactors for main fermentation of beer. The a-ALDC enzyme produced by the transformant catalyzes the direct conversion of a-acetolactate to acetoin without formation of diacetyl. The long lagering period required for beer maturation in conventional brewing can thus be shortened or even omitted.Three different packed bed bioreactors were employed, with volumes of 1.6 dm3, 5 dm3 and 25 dm3.The 5 dm3 column had a slightly conical geometry in contrast to the others which had cylindrical shapes. Sintered glass beads were chosen as the carrier material on the basis of experiments with the parent strain.The brewing performance of the transformant compared well with that of the parent strain in the immobilized system. Fermentation, utilization of amino acids (including isoleucine, valine and leucine) and flavour formation were practically identical with both strains, the only difference being a marked decrease in the formation of diacetyl by the transformant. Small differences were, however, observed in the long-term biochemical stability.By using yeast encoding a-ALDC in the immobilized yeast system the total (primary and secondary) fermentation time could be reduced to approximately 2-6 days, compared with 3-6 weeks in a conven tional batch process.

Lactic acid bacteria (LAB) are known as predominant beer spoilers. They cause turbidity, acidity, gas formation and offflavors in beer by formation of side metabolites. Beer spoiling LAB have a substantial financial impact in the brewing industry making their rapid detection and identification essential. Despite the developed rapid diagnostic methods, the bottleneck in detection remains the lengthy enrichment cultivation step. This paper describes the applicability of a novel glucose auto delivery system, EnBase™, for the improved enrichment cultivation of beer spoiling LAB in MRS medium. By means of the applied system, glucose is slowly released into the culture during growth, which results in faster enrichment. Growth of Lactobacillus brevis DSM 20054 T and several beer spoiling LAB was accelerated resulting in up to a 300% increase in the cell density after 48 h of cultivation compared to the commonly used MRS medium. A test of naturally contaminated beer samples indicated that the addition of glucose by means of EnBase allows faster detection of LAB in breweries.

J. Inst. Brew. 116(2), 151-156, 2010The beer spoiling lactic acid bacteria (LAB) are known to have a substantial financial impact in the brewing industry and their rapid detection is essential. Thus more effective media for the cultivation of LAB in both routine quality control and special trouble-shooting situations are needed. In this study, different media were tested for the routine detection of LAB at a commercial brewery. The results showed that the use of an enzyme controlled glucose delivery system, in combination with beer-MRS medium, can significantly decrease the total analysis time. For more effective trouble-shooting in contamination incidents a trouble-shooting media, including the reducing agents L-cysteine-HCl and sodium bicarbonate, was developed. The presented medium was shown to improve the growth of beer spoiling L. backi and L. brevis, and is thereby suggested for faster detection of these strains at the breweries.

Beer‐spoiling lactic acid bacteria (LAB) belong to the most harmful contaminants in the brewing industry and various rapid molecular detection methods have been introduced for the detection of these organisms. However, the enrichment cultivation steps needed prior to detection by molecular methods can extend the duration of the analytical procedure by up to several days. The use of brewery‐specific enrichment cultivation media has been recommended due to the large variety within the group of LAB, as well as differences in the microbes encountered at the breweries. In contrast to using a general medium that may support only the growth of some LAB, the combination of several media could allow detection of all relevant LAB. The aim of the present study was to show the effects of shifts in the cultivation conditions and media on the growth of beer‐spoiling LAB using one of the most frequently encountered species, Pediococcus damnosus, as an example. Based on the variable analysis, significant factors could be recognized and their effects on lag‐times and growth rates were compared by means of response surface modelling.

Various molecular methods have been developed for the rapid microbiological analysis of beer and brewing process samples. However, enrichment cultivation is still needed in order to reach the detection limits of the molecular assays, and it may directly contribute to the costs and accuracy of detection. The selection of proper enrichment cultivation conditions may be complex due to the wide variety of available media, and controversial reports of their performance. Therefore, this article aims to clarify this process by summarizing the main factors affecting the growth of lactic acid bacteria (LAB) in the enrichment cultures and reported media for this purpose.

Microbiological contamination of immobilized yeast bioreactors for lagering of beer was studied. Four common brewery contaminants and two contaminants isolated from the continuous processing system were tested for their ability to survive and grow in the packed bed DEAE-cellulose bioreactors. Bacterial contaminants were washed out within less than six weeks without causing any alterations in the flavour composition of the beer. The initial contamination levels were lOMO6 cells ml"1. Gram positive lactic acid bacteria, Lactobacillus brevis and Pediococcus damnosus, were more persistent than a Gram negative wort bacterium, Enterobacter agglomerans.The wild yeasts Saccharomyces cerevisiae (ex. diastaticus) and Candida krusei were the most persistent contaminants and the only ones able to grow in the reactors. Another wild yeast, Rhodotorula rubra, did not survive in competition with brewer's yeast and was washed out within a few weeks. C. krusei and R. rubra were previously isolated from a spontaneously contaminated system. None of the contaminants caused formation of phenolic or other off-flavour compounds in detectable levels.

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