The following table shows the characteristics of three differnent styles of Lambic Beer:
|Alcohol (g/100 ml)
|Ethyl acetate (ppm)
The soft and hard classifications are due primarily to the acid contents of the beer, whereas the rope characteristic describes the oily consistency of the beer due to high lactic acid levels.
The finished product is characterised by high levels of lactic acid, acetic acid, ethyl acetate and ethyl acetate. Final gravities are in the region of 1.008 (2.2 oP) 1.012, 3 oP, DMS levels are reduced to approx 100pb and diacetyl concentrations between 45-80ppb. Final 2,3 butanediol levels are not available.
Beers of the lambic style are described as having vinous aromas and tastes accompanies by ‘horse blanket’ or ‘goaty’ characterisitics, which appears to be attributable to the contained acids and products from Brettanomyces activity. Thin mouth feel is also noted, due to the low levels of residual dextrins.
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The spontaneous nature of lambic fermentation and the varied spectra of bacteria and yeasts encountered in differing breweries that are responsible for such fermentation, may produce beers with differing characterisitics.
Brettanomyces species, particularly B. limbicus and B. bruxellensis also become active during this period, from approximately 8 months onward (figure to follow). These yeasts are capable of fermenting dextrins (found in relatively high levels in lambic wort), maltotriose and maltotetraose, producing small amounts of acetic acid and ethanol. However, it is the production of unique flavour and aroma compounds that characterises the activity of Brettanomyces. Brettanomyces exhibits a high esterase activity, primarily resulting in the synthesis of large amounts of ethyl acetate and ethyl lactate. This esterase also cleaves iso- amyl acetate esters, thus accounting for its low concentration in lambic beer.
Tetrahydropyridines are also produced from ethanol and the amino acid lysine, which impart a ‘mousy’ or ‘horsy’ aroma to the beer. Volatile phenolics, with medicinal, ‘barnyard’ or ‘animal’ type odours are also from from 4-ethyl phenol and 4-ethyl guaiacol compounds.
Brettanomyces activity also leads to a significant increase in caprylic (C8) and caprix (C10) acids (small amounts are formed during earlier Saccharomyces acitivity) along with their associated esters, ethyl caprylate and ethyl caprate. These compounds produce a characteristic ‘goaty’ aroma/flavour to the final product. Capric and caprylic acids are short chain fatty acids and are thought to be by-products of yeast metabolism, produced during lipid synthesis by a yeast cell and released into the medium via leakage through membranes damaged by ethanol, or as a consequence of an autolytic mechanism. Higher temperatures, aeration and agitation during fermentation reduce the amounts of fatty acids in beer. Reduced aeration/agitation produced higher concentrations. The combined threshold for C6-C12 acids is 10ppm, beyond which ‘goaty’ aromas arise. C8 acid levels in gueuze as 12.4 – 21.85 ppm and C10 acids as 2.3 – 3.9p ppm.
Brettanomyces is active until the end of the fermnetaion period. Acetic acid bacteria of the genus Acetomonas and a number of oxidative yeasts (Pichia, ) are also found during lambic fermentations, however their influence is often minimal.
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