Challenging the assumptions around the pasteurisation requirements of beer spoilage bacteria

Abstract

Current recommendations for beer pasteurisation are based on the study in 1951 by Del Vecchio and coworkers. 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°C. 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. Validation of pasteurisation at a range of pasteurisation units (PU) in packaged product were performed in a tunnel pasteuriser. 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. 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. In package pasteurisation conducted at 1.6 PU resulted in greater than an 8‐log reduction in viable cell numbers, resulting in ‘commercial sterility’. 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. © 2018 The Institute of Brewing & Distilling

Heat resistance of yeast ascospores and their utilisation for the validation of pasteurisation processes for beers

“…Two bacterial species, Lactobacillus brevis BSO 566 (which was found to be the most heat resistant bacterium in our previous study ( 16 ) ) and Lactobacillus lindneri BSO 943 – an emerging beer spoilage microorganism ( 17 ) ‐ were employed. The bacteria were stored in liquid nitrogen.…”

“…The D‐value is the time required at a specific temperature for a decimal (i.e., 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. To show that the heat resistance of yeast ascospores are significantly greater than the heat resistance of a typical beer spoilage vegetative bacteria, additional heat inactivation trials were performed with the common beer spoilage microorganisms; Lactobacillus brevis (which has been found to be one of the most heat resistant beer spoilage bacteria in a similar study) ( 16 ) and Lactobacillus lindneri (an emerging beer spoilage bacteria) ( 17 ) .…”

Screening and Application of Cyberlindnera Yeasts to Produce a Fruity, Non-Alcoholic Beer

“…Due to the high amounts of residual sugars, proper pasteurization is essential for non-alcoholic beers produced by limited fermentation to avoid microbial spoilage [1,38,53]. After bottling, C6.1 NAB was therefore pasteurized with approximately 23 PU, and the successful pasteurization was confirmed by plating the pasteurized NAB on agar to check for microorganism growth, which was found to be negative.…”

Innovative Rough Beer Conditioning Process Free from Diatomaceous Earth and Polyvinylpolypyrrolidone

“…Despite an LRV value of 5–7 is normally believed acceptable for food and beverage applications, the EBC Manual of Good Practice [ 39 ] recommends a minimum commercially sterility of 15 or 20 PU for Pilsner and lager beers or ale and stout, respectively, this indicating a >8.7 log reduction in the cell numbers of the selected organisms [ 40 ]. Such EBC recommendations refer to the studies carried out as long ago as 1951 [ 41 ].…”

“…In all probability, the high heat loads involved during beer pasteurization result in damage to aroma and flavor compounds [ 42 ]. As pointed out by Rachon et al [ 40 ], the EBC guidelines were composed more than 20 years ago and hygiene in breweries has by far improved since then. Thus, lower PUs and, consequently, lower LRVs, as those achieved with current membrane filters, should be today sufficient to achieve microbial stability in beer [ 40 ].…”