Identification of spoilage microflora in draught beer using culture-dependent methods

AIMS

To determine whether the culture-dependent spoilage microflora found in draught beer are influenced by beer style.

METHODS AND RESULTS

Four beer styles - lager, ale, stout, and cask ale - were sampled twice from five different public houses (accounts) in four different locations. The microbiological quality of the dispensed beers was determined by a culture-dependent method ('forcing'), measuring the increase in turbidity after incubation at 30°C. The quality of draught beer varied from 'excellent' to 'poor' with cask beer samples having a higher Quality Index (90%) with keg ale the lowest (67.5%). With PCR amplified DNA (ITS1, ITS4, 16S rRNA primers) and BLAST identification of microflora, 386 colonies from agar plates were identified with 28 different microorganisms from five genera of yeast and six of bacteria. Seven microorganisms were found in all beer styles with Brettanomyces bruxellensis, B. anomalus and Acetobacter fabarum representing 53% of the identified microorganisms. A subsequent, limited study using PALL multiplex PCR GeneDisc technology on forced samples (without selection on plates) suggests that draught beer microflora is qualitatively broader. It is noteworthy that the microflora of spoilt draught beer resembles that involved in the production of Belgian Lambic sour beers.

CONCLUSIONS

Draught beer was of variable quality. Culture-dependent analysis suggests that species of Brettanomyces and Acetobacter are core microflora with some microorganisms being associated with beer style.

SIGNIFICANCE AND IMPACT OF THE STUDY

The microbiological quality of draught beer is important both commercially and to the Consumer. Here, we report the core and diverse microflora found in different styles of draught beer using culture-dependent methods.

Detection and enumeration of Dekkera anomala in beer, cola, and cider using real-time PCR

AIMS

In this article, a quantitative real-time PCR assay for detection and enumeration of the spoilage yeast Dekkera anomala in beer, cola, apple cider, and brewing wort is presented as an improvement upon existing detection methods, which are very time-consuming and not always accurate.

METHODS AND RESULTS

  Primers were designed to exclude other organisms common in these beverages, and the assay was linear over 6 log units of cell concentrations. The addition of large amounts of non-target yeast DNA did not affect the efficiency of this assay. A standard curve of known DNA was established by plotting the C(t) values obtained from the QPCR against the log of plate counts on yeast peptone dextrose medium and unknowns showed exceptional correlation when tested against this standard curve. The assay was found to detect D. anomala at levels of 10-14 CFU ml⁻¹ in either cola or beer and at levels of 9·4-25·0 CFU ml⁻¹ in apple cider. The assay was also used to follow the growth of D. anomala in brewing wort.

CONCLUSIONS

The results indicate that real-time PCR is an effective tool for rapid, accurate detection and quantitation of D. anomala in beer, cola and apple cider.

SIGNIFICANCE AND IMPACT OF THE STUDY

This method gives a faster and more efficient technique to screen beer, cola, and cider samples and reduce spoilage by D. anomala. Faster screening may allow for significant reduction in economic loss because of reduced spoilage.