Premature yeast flocculation (PYF) is an unwanted condition that occurs during the fermentation of wort in which yeast settles out of the medium at an accelerated rate compared to normal fermentations. This leaves the fermented wort under attenuated, often requiring substantial troubleshooting to render the beer saleable. In extreme cases the beer cannot be sold. Traditionally, PYF events were considered sporadic, but recent arguments suggest that PYF may be a problem that is more common than previously thought. Even though PYF is a world-wide dilemma its nature and mechanisms are still not completely understood. Building on previous reported results the present study focuses on three aspects of PYF: (1) methods of detecting PYF, (2) mechanisms of PYF factor interaction with yeast and (3) the active components of the PYF-inducing factor(s). With regards to methods of detection a small volume (15 mL) fermentation assay was developed. Previous attempts at small scale fermentation assays often failed as yeast falls out of suspension due to insufficient average shear rates in the fermentor. It was determined that the addition of 4% glucose (w/v) and fermenting at 21°C compensated for height reductions yielding adequate average shear rates to keep yeast in suspension in the 15 mL test tube fermentation. This low volume fermentation improved on tall tube fermentors detecting PYF worts in 48 hr while requiring less wort. A photometric device was constructed to examine yeast in suspension more thoroughly in small scale fermentors. Uninterrupted measurement of fermentations yielded over 800 data points that were subsequently modelled using a non-linear application of two general logistic curves. Although the model proved to be an accurate means of statistically identifying a PYF wort compared to a control, the amount of data required did not allow the non-linear technique to be applied to normal fermentations. Addition of methyl alpha-D-manno-pyranoside, a known inhibitor of yeast zymolectins, did not interrupt PYF activity suggesting zymolectins are not directly involved in PYF. Furthermore, an affinity assay composed of yeast immobilized in acrylamide was developed to purify PYF factors. Since the assay was unsuccessful it is believed that PYF occurs via methods different then those previously hypothesized in the literature. To keep PYF factors as close to their native composition as possible, filtration and small scale fermentations were utilized to isolate and determine active PYF components. Through a series of membrane filtrations it was determined that removal of PYF wort components with molecular weights >100 kDa reduced the PYF activity. The re-introduction of these 100 kDa components into a normal fermenting wort induced PYF. Several fermentation tests with both the 100 kDa PYF-inducing retentate and a series of pure standards indicated that ferulic acid is most likely to be directly involved in the activation of PYF.
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