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.