The role of acetic acid bacteria in brewing and their detection in operation

Abstract

Acetic acid bacteria (AAB) are often considered a threat of the past because today’s equipment allows to perform post-fermentation processes under greatly reduced level of oxygen. This paper deals with the current importance of AAB in brewing. The risk of contamination as well as functional role in spontaneously fermented sour beers is reviewed. The main harmful effect of AAB lies in the direct spoilage of draft beer and formation of biofilms, most often in dispensing systems. On contrary AAB seems to be indispensable in the case of sour beer production. A key issue of AAB in brewing environment is their (early) detection and identification. Therefore, part of this study is devoted to both the latest sophisticated methods and also those of traditional cultivation. which are still prevalent in operating laboratories due to their cost and easy implementation. Finally, the experimental and pictorial material is added as a guide for operations that have less experience with AAB.

Acetic Acid Bacteria in Sour Beer Production: Friend or Foe?

“…Nowadays, for almost all beers produced the fermentation relies on specific yeast strains and the presence of bacteria is completely undesirable due to their spoilage potential ( Briggs et al, 2004 ; Vriesekoop et al, 2012 ). However, although their spoilage capacity, some specific beers do require LAB and/or AAB to introduce characteristic beer flavors ( Van Oevelen et al, 1977 ; De Keersmaecker, 1996 ; Tonsmeire, 2014 ; De Roos and De Vuyst, 2019 ; Bongaerts et al, 2021 ; Kubizniaková et al, 2021 ). Sour beers, with their typical refreshing and (slightly) acidic flavor because of high organic acid concentrations are an example of such beers, during the production process of some LAB or even both LAB and AAB are part of the core microbiota and hence contribute to their flavor formation ( Van Oevelen et al, 1976 ; Snauwaert et al, 2016 ; De Roos and De Vuyst, 2019 ; Bongaerts et al, 2021 ).…”

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

“…Acetic acid bacteria oxidize ethanol to acetic acid (Kubizniaková et al, 2021), and although aerobic, Gluconobacter species are ‘capable of developing at very low oxygen tensions’ (Ault, 1965). Whilst in the 1940s much feared in breweries, acetic acid bacteria are no longer a concern with closed vessels, packaging in kegs, significantly improved hygiene and oxygen stringently minimized to assure flavour stability of the product.…”

“…Whilst in the 1940s much feared in breweries, acetic acid bacteria are no longer a concern with closed vessels, packaging in kegs, significantly improved hygiene and oxygen stringently minimized to assure flavour stability of the product. However, the threat of acetic acid bacteria and associated vinegar taint in cask beer (Ault, 1965) remains a concern (Kubizniaková et al, 2021; Quain, 2015). Ingress of oxygen inevitably occurs during the dispense of cask beer and 46% of the microflora identified in cask ale samples were acetic acid bacteria.…”

“…Whilst presumably planktonic, micro‐organisms in dispensed keg lager, ale, stout and cask ale can form biofilms when incubated in microplates (Jevons & Quain, 2021). Indeed, many of the micro‐organisms in Table 2 have been identified in dispense biofilms including acetic acid bacteria (Kubizniaková et al, 2021; Thomas & Whitham, 1996), Lactobacillus species (Walker et al, 2007), Pediococcus (Heger & Russell, 2021; Thomas & Whitham, 1996) and Saccharomyces species (including S. diastaticus ) (Riedl, Fütterer, et al, 2019; Walker et al, 2007). Elsewhere biofilm formation has been reported for B. bruxellensis from beer in wine (Dimopoulou et al, 2019), R. mucilaginosa (Riedl, Fütterer, et al, 2019) in beer, some (but not all) 20 brewery isolates of L. brevis in beer (Riedl, Dünzer, et al, 2019) and five species of Lactobacillus in beer (Wang et al, 2020).…”

“…and high in ethanol (4%–8% ABV) with a low pH (<4.2) and contains antimicrobial bitter substances derived from hops. Despite this, draught beer is susceptible to spoilage by a limited but diverse range of micro‐organisms (Quain, 2015), including aerotolerant gram‐positive bacteria ( Lactobacillus , Pediococcus ; Suzuki, 2015), aerobic Gram‐negative bacteria ( Acetobacter , Gluconobacter ; Kubizniaková et al, 2021), facultatively aerobic yeasts ( Saccharomyces ) and aerobic yeasts ( Brettanomyces , Pichia , Rhodotorula ; Powell & Kerruish, 2017).…”