Application of a Newly Developed Method for Estimating the Premature Yeast Flocculation Potential of Malt Samples

Flocculation is prerequisite for bulk sedimentation of yeast during brewery fermentation. Although single yeast cells gradually sediment in green beer, this sedimentation rate is too slow without formation of large yeast flocs. The present review concerns the major determinants of yeast flocculation and sedimentation in brewery fermentations. Flocculation characteristics of yeast are strongly strain-dependent and largely defined by which FLO genes are functional in each strain. In addition to the genetic background, several environmental factors affect flocculation. These can be, somewhat arbitrarily, classified as physiological factors, such as the calcium availability, pH, temperature and ethanol and oxygen concentrations in the medium or physical factors, such as cell surface hydrophobicity, cell surface charge and the presence of appropriate hydrodynamic conditions for the formation of large flocs. Once yeast flocs are formed, their size, shape and density and the properties of the surrounding medium affect the rate at which the flocs sediment. Higher gravity worts usually result in green beers with higher viscosity and density, which both retard sedimentation. Moreover, environmental factors during yeast handling before fermentation, e.g., propagation, storage and cropping, influence the flocculation potential of yeast in subsequent fermentation. Premature yeast flocculation (PYF) and the role of PYF factors are discussed. In conclusion, some potential options available to adjust yeast flocculation are described.

Section: Premature Flocculation Associated With Malt Qualitymentioning

confidence: 99%

“…Most are fermentation tests that take several days to perform, such as the method described by Jibiki et al 31 , which makes use of a PYF-sensitive lager yeast. Koizumi and Ogawa 40 have developed a rapid method to measure the PYF activity of barley, malt or wort (Rapid Kirin test).…”

Section: Premature Flocculation Associated With Malt Qualitymentioning

confidence: 99%

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

Vidgren

Londesborough

2011

“…The assay consisted of small-scale fermentations and is based on similar existing methods 7,15,29 . Yeast cells in the stationary phase were aseptically transferred into 250 mL centrifuge tubes and were centrifuged at 50,000 × g for 5 min at 25°C.…”

Section: Wort Composition Analysesmentioning

confidence: 99%

“…Despite these issues, detection of malts responsible for PYF during fermentation is of major importance to both the maltster and the brewer 15 . As standard malt analysis is unable to predict PYF fermentation potential 4,20,31 , small scale fermentation tests have been developed to perform this key function [8][9][10][11]13,20,22,30 .…”

Section: Introductionmentioning

confidence: 99%

Optimization of a Small-scale Fermentation Test to Predict the Premature Yeast Flocculation Potential of Malts

Panteloglou

Box

Smart

et al. 2010

J. Inst. Brew. 116(4), 413-420, 2010Rapid and early detection of malts likely to cause premature yeast flocculation (PYF) is of major importance both to the brewer and the maltster. To date, the most reliable and widely applied diagnostic tests for predicting the PYF status of malts involve conducting a small scale fermentation test, which usually takes several days to be completed. This study investigated the impact of selected factors on the ability of such a test to distinguish between PYF positive and PYF negative malts and the fermentation time after which the test results, and therefore the PYF status of the malts, could be confirmed. The results obtained suggest that the PYF potential of malts could be predicted 40 hours post pitching by adding 6 mg.L -1 linoleic acid and using a highly flocculent PYF sensitive yeast strain.

“…However, concern has arisen over the use of visual examinations of absorbance curves and the absence of statistical rigour when quantifying the PYF properties of sample malts. Two studies have reported statistically treated data consisting of one or multiple time measurements 2,5 . However, in both cases the data from the entire fermentation was not used.…”

Section: Introductionmentioning

confidence: 99%

Modelling of Yeast in Suspension During Malt Fermentation Assays

Lake

Speers²,

Gill

et al. 2009

Premature yeast flocculation (PYF) is a poorly understood condition leading to attenuation of fermentation and poor alcohol yields. The yeast in suspension in fermenting worts prepared from either normal or premature flocculating malts was continually measured during the small 15 mL fermentation test recently developed in the Dalhousie laboratories. A simple inexpensive monitoring system was constructed from a laser level, photometric cell and data logger. This system allowed non-destructive data collection of absorbance data (over 700 data points per fermentation) at ~650 nm. A non-linear modeling technique was applied to the data, and yielded two best-fitting logistic models. The model parameters were quantitatively compared to determine if statistical differences between PYF and normal wort were apparent. A student's t test of the logistic parameters indicated a significant difference (p > 0.025) between control and PYF worts for the increase in absorbance at the beginning of the fermentation. A significant difference (p > 0.0001) in the inflection time of absorbance down-curve between the control and PYF wort was also noted.