The Beer Brewer

The beer at this point contains 1000ppm lactic acid, 1000ppm 2,3-butanediol, 250ppm succinic acid, 200ppm acetic acid and 100ppm formic acid. Flacours identified as sweet, honey, fruity, vegetbale or faecal are associated with compounds produced by the Enterobacteriaceae. The slow emegence of the the predominant Saccharomyces species, S. cerevisiae and possibly S. globus is a result of the depletion of wort amino acids by Enterobacteriaceae activity. This signifies the primary period of alcohol production, during which 80% of the wort sugars (glucose, fructose, sucrose, maltose, and maltotriose) are metabolised via the EMP pathway. Ethanol and CO2 are the primary end products. Pre-formed volatile compounds (esters and DMS) may be driven out of the beer by CO2 evolution during this phase.

Higher, or Fusel alcholol synthesis is a feature of Saccharomyces fermentation, occurring during ethanol production. The fusel alchohols impart a plastic or solvent like flavour to the beer. Elevated levels of propanol, amyl alchohol, isobutanol, isoamyl alcohol and phenylethyl alchohol are not noted in lambic beer and are ths not distinctive flavour/aroma components of the style.

A significant proportion of the lambic esters, particularly ethyl acetate and ethyl lactate are produced during this period. Ester impart a full-bodied, floral/fruit flavour/aroma to beers. Excessive levels (noted in lambic beers) may lead to off or overly fruity flavours. Ethyl acetate is formed by a cellular esterification pathway within the yeast cell by a reaction between acetyl-CoA compounds and alcohol, catalysed by the acyl-alcohol transferase enzyme. The resulting ester produces a fruity/solventy taste in the beer and has a threshold detection level of 33pm. The increased ester formation is promoted under the following conditions: Wort density about 13o P, increasing attenuation levels, increasing fermentation temperatures, increasing agitation during fermentation and reducing wort aeration levels. The inverse of these conditions reduce ester formation. A profile of beer components at this stage indicates wort gravity decreased to approx 1.012, alchohol content is 4.5 - 5% v/v, butanediol content is unchanged whilst DMS levels are reduced.

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 .

An Introduction to Lambic Beers

The Belgian lambics are unique beers, traditionally produced in the Payottenland region of Belgium, via a process of spontaneous fermentation, as opposed to the controlled inoculation and fermentation procedures used in the production of other beer styles. This type of traditional, spontaneous fermentation is employed in combination with differing raw materials and production processes, to produce beers with unique flavour and aroma profiles, which have not been reproducible via other methods. Spontaneous fermentation is facilitated by overnight exposure of the cooling (un-inoculated) wort to the predominant air borne microflora of the brewery, which rapidly establish themselves within the wort.

There are two major phases of fermentation underaken in lambic beer, both involving the activities of bacteria and yeast; a primary phase, lasting for 3-4 months, characterized by the production of high amounts of ethanol; and a second, slower period of “lambification” or acidification, lasting for 12-24 months. A subsequent third (bottle) fermentation phase may be used to produce a gueuze style lambic.