The Beer Brewer

Continuing our article on Lambic Beers …

The primary phase of lambic fermentation occurs after the “infected” wort is transferred into the fermentation casks. Typical initial temperatures are between 18-20oC, with initial specific gravities ranging from 1.048 - 1.072, depending upon lambic style produced. Initial fermentation during this period is due to the activity of bacteria from the Enterbobacteriaceae family and Kloeckera yeast strains. The cooling wort is readily colonised by the Enterbobacteriaceae, with strains of Enterobacter cloacae and E. aerogene being indicated as the predominant species. Strains of Klebsiella aerogene, Escherichia coli, Citrobacter freundii and Hafnia alevi are also active at this point. All species are capable of fermenting glucose and/or lactose via the Embden-Meyerhof-Parnas (EMP) pathway, but cannot utilise maltose or maltotriose.

The Enterobacter, Keibsiella and Hafnia species utilise a butanediol fermentation, producing 2,3-butanediol, acetoin and ethanol from the metabolism of glucose. E. coli and C. freundii employ a mixed acid fermentation to primarily produce lactic acid and lesser amounts of acetic, succininc and formic acids, ethanol and CO2. The activity of the latter species results in the formation of the majority of acetic acid found in lambic beer. This bacterial activity also results in the production of large amounts (500ppb) of DMS.

The activity of Kloeckera apiculata, a yeast capable of mixed acid fermentation from the metabolism of glucose, during this phase has little impact upon the lambic flavour, as any volatile esters it may produce are lost due to subsequent CO2 evolution. The combination of bacteria and yeast growth within this period has minimal impact upon the worts fermentable sugars, a maximum attenuation of 15% may be realised, however a significant drop in wort pH is apparent, from 5.1 to 4.6 as a resul primarily of acid formation. K. apiculata is gradually supplanted after two weeks by the apperance of the Saccharomyces species, whilst the Enterobacteriaceae disappear after 30-40 days, due to their sensitivy to ethanol concentration above 2% and pH leveles below 5.5 .