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The Influence of Fermentation-Control on the Colloidal Stability and the Reducing Power of the Resulting Bottom Fermented Beers
Pschl, M., Bauer, S., Leal, L., Illing, S., Stretz, D., Wellhoener, U., Tenge, C., Geiger, E.

The focal point of this work was to evaluate variations in fermentation-control, which included different fermentation temperatures and different pitching rates, the usage of yeast from various numbers of generations as well as the application of pressure fermentation. Of particular interest was the monitoring of haze relevant polyphenols and proteins as well as the detection of antioxidative capacity, which was differentiated between fast reducing substances and total reducing power. The force tests showed reproducible lower formation of colloidal haze in the beers resulting from fermentation at lower temperatures and from decreasing numbers of yeast generations. Also lower pitching rates and pressure fermentation seem to improve colloidal stability. The best reducing power, which does not influence colloidal stability in either case, resulted from cold fermentation and higher pitching rates. It has been shown that variations in the field of fermentation performance may have an impact on the colloidal stability. Thus optimising the fermentation performance and pitching technology can be regarded as one further step to improve colloidal stability in a technological way. Preservation of colloidal stability in bottom fermented and filtered beers has emerged as one of the biggest challenges breweries have to meet in the current beer markets, which exhibit an ever increasing tendency to globalisation combined with rising consumer-expectancy to the clarity and quality of beer. Main haze forming substances in the bottled beer are polyphenols (first of all flavan-3-ols) and proteins. However, also polysaccharides, minerals and metal ions can be detected in haze [1,2,3,4,5,6,7]. Thus colloidal stability mainly depends on the composition of the raw materials malt, hops and brewing water. In addition to a precise selection of raw materials one further way to improve stability is the usage of stabilisation agents. The latter method is quite effective but results in a loss of potentially physiologically active beer components e.g. the polyphenols, to say nothing of the increased costs for stabilisation. One focal point of current research is therefore the stabilisation in a technological way by optimizing the brewing process with regard to lower haze formation. Knowledge about the influence of fermentation control on the colloidal stability and the performance of haze relevant substances during fermentation is still quite low. It has been reported that the concentration of haze sensitive polyphenols decreases during fermentation, most likely caused by the bonding to proteins in the yeast-cell wall. The content of haze relevant substances then increases again at longer storage periods [8,9]. In contrast Bellmer has not found a considerable decrease of flavan-3-ols during fermentation but during storage [10]. Up to now no experiments have been conducted to get more detailed information on the effect of variations in fermentation-control on colloidal stability. The aim of this work was to evaluate the influence of fermentation-control on the colloidal stability and the reducing power of the resulting beers. In this regard, the polyphenolic spectrum of wort and beer has been measured by HPLC. Further investigation scopes were the effects on the reducing power, detected by electrochemical methods, as well as on the concentrations of haze sensitive proteins in the beer. Bitter wort (for Pilsner- and Lager beer) was used in these tests: Original gravity 11.3-12.0 g/100 g, final attenuation degree 80-86 %, pH 4.8-5.1. In each sample of one test-batch the same wort was used. Wort was fermented in 20 l fermentation tanks after 10 min. aeration with a sinter candle under pressure (final oxygen content 8-9 mg/l). Yeast strain: W 34/78; pitching rate ~15 Mio cells/ml (if not indicated otherwise), fermentation temperature differed concerning the approach (see below); at attenuation degree of ~78 %: cooling of the green beer to 4 C for 24 h and cropping of the yeast; maturation for 1 week at 4 C, removal of the spent yeast; storage for 2 weeks at 0 C; beer filtration with a combined kieselguhr/sheet filter (sheets 0.6 m); Bottling and capping in standard 0.5 l NRW-bottles. Differentiation of the experiments:A) Fermentation Temperature: 6 tests; each test included the comparison of 3 different fermentation temperatures. 3 tests were conducted to compare 9 C, 11 C and 13 C-fermentation (approach 1), 3 other tests compared 9 C, 12 C and 15 C-fermentation (approach 2)

Descriptors: colloidal stability, haze, reducing power, fermentation, yeast

BrewingScience Monatsschrift fr Brauwissenschaft, 60 (July/August 2007), pp. 96-109