| Premature yeast flocculation (PYF) is an intermittent yet devastating problem that can on occasion plague the brewing and malting industries. The timing of yeast flocculation is very important in achieving the correct fermentation characteristics. Suitable brewing yeast strains must be able to ferment wort sugars and flocculate towards the end of the exponential phase of growth. When premature yeast flocculation occurs, the yeast settle out of suspension rapidly resulting in low attenuation, low end of fermentation cell counts and undesirable beer flavours such as high diacetyl levels. All of this results in financial losses for the brewer and maltster.; Worts were prepared from PYF-positive and PYF-negative malt samples. The composition of the worts was extensively analyzed by high performance liquid chromatography, fast protein liquid chromatography and gas chromatography. Differences in carbohydrates, lipids and peptides were measured. No apparent differences existed in wort peptides in the malt samples examined.; The worts were fermented using two separate fermentation tests, a 3.5 mL cuvette test and a 15 mL glucose supplemented test. The fermentations examined the effect of malt quality on yeast growth and attenuation. The glucose supplemented test was able to demonstrate PYF differences in the wort samples examined. In the case of cuvette fermentations all wort samples had similar fermentation profiles. While, the PYF factor has been hypothesized to act by inhibiting sugar uptake, the cuvette test results suggested no difference in sugar uptake existed in the worts examined. |
