14 reported higher z-values for common beer spoilage bacteria. Similarly, Tsang and Ingledew 13 and Molzahn et al. 12 reported the failure of a flash pasteurisation at 26.5 PU owing to the presence of an L. Despite a number of concerns 9- 11 associated with using Del Vecchio's z-value (6.94☌), it is still widely used. These EBC recommendations are based on a historical study, conducted by Del Vecchio et al.
The European Brewery Convention (EBC) Manual of Good Practice 6 provides basic recommendations for pasteurisation of a range of beer styles (Table 1), but it is suggested that the stated heat loads are over-estimated, resulting in over processing of the beverages, which may result in damage to aroma and flavour compounds 7. 1 log or 90%) reduction in the population of a microorganism the z-value is defined as the change in temperature required for a 10-fold change in the D-value. The D-value is the time required at a specific temperature for a decimal (i.e. The brewing industry currently bases its pasteurisation regimes on long-established microbiological parameters: D- and z-value, and pasteurisation units (PU) of an organism under certain conditions 6. Therefore, selecting the most suitable time–temperature pasteurisation regime for a particular product is not always straightforward. Thermo tolerant bacteria and yeast are able to tolerate standard heat treatment regimes. To combat these contaminants, pasteurisation is widely employed in the brewing industry however the effectiveness of the process varies depending on the processing time and temperature, product composition and the type of contaminating organisms present 5. It is anticipated that futher work will study the heat resistance of spoilage bacteria in biofilms and yeast ascospores. A number of yeast species can also spoil beer however, this study focused on bacteria. Acetobacter spp.), Zymomonas spp., Megasphaera spp., Kocuria spp. In addition, there are other aerobic and anaerobic beer and brewery-related spoilage organisms that represent a potential source of contamination in the brewing environment and where beer is served in a draught dispensing system, such as acetic acid producing bacteria (e.g. Approximately 70% of beer spoilage cases result from contamination by species of Lactobacillus and Pediococcus 1, while Lactobacillus brevis has been reported as the most prevalent spoilage organism, regardless of the beer style investigated 2. © 2018 The Institute of Brewing & DistillingĬontamination of beer is an important problem for the brewing industry, necessitating sterile filtration or heat treatment to maintain the biological integrity of the product. Although this study demonstrated that successful pasteurisation was achieved for vegetative cells at significantly lower PU values than those recommended, further studies are required to demonstrate the optimal level of pasteurisation for spore forming bacteria and for yeast. In package pasteurisation conducted at 1.6 PU resulted in greater than an 8-log reduction in viable cell numbers, resulting in ‘commercial sterility’.
Effective pasteurisation of the selected microorganisms was achieved at significantly lower PU values than those recommended by the European Brewery Convention Manual of Good Practice.
This study showed that eight of the 14 microorganisms were able to grow in both beer styles, whilst different thermo tolerances were observed amongst the spoilage bacteria.
Validation of pasteurisation at a range of pasteurisation units (PU) in packaged product were performed in a tunnel pasteuriser. Using a capillary tube method, the D-value (decimal reduction time) and z-value (temperature resistance coefficient) of the three thermo tolerant bacteria ( Acetobacter pasteurianus, Lactobacillus brevis and Lactobacillus hilgardii) were determined. In this work, 14 beer spoilage bacteria were screened for their ability to grow or survive in ale and stout together with the determination of their thermo tolerance at 60☌. Current recommendations for beer pasteurisation are based on the study in 1951 by Del Vecchio and coworkers.