Fermentations with flocculating lager yeast at 7.4 degrees C were carried out with normal pitching rates of 5 g wet yeast per litre and at double and fourfold rates. Daily samples were centrifuged to collect the yeast which was disintegrated ultrasonically for measurement of the enzymic activities. At normal pitching rate, 61.5% attenuation was reached at 216 h, with double rate 66.5% at 168 h and with fourfold pitching 69% attenuation was reached at 144 h. The various determinations were calculated as relative to the attenuation rather than at fixed time intervals. At normal pitching rate the beer contained 10 g wet yeast/litre when fully attenuated, with double and fourfold pitching the corresponding yeast crops were respectively 9.6 g and 7.6 g. The beer with normal pitching rate showed better absorption of amino acids, vitamins and nucleotides so was presumably more stable biologically. With normal pitching the yeast crop contained more calcium and magnesium but much less Fe, than with higher pitching rates. Manganese and zinc were similar in all crops, copper content was similar at normal and double pitching rates but was 4 times greater with fourfold pitching. The enzyme activity increased during fermentation with increased pitching rate for lactate dehydrogenase and glycerol kinase. The enzyme activity decreased during fermentation with increased pitching rate for maltotriase, maltase, hexokinase, phosphofructokinase, phosphoglyceraldehyde dehydrogenase, pyruvate kinase and decarboxylase, alcohol dehydrogenase, citrate synthase, fumarase and glucose 6 phosphate dehydrogenase. Low enzyme activities were produced at the higher pitching rates for isocitrate dehydrogenase and malate dehydrogenase. In general the activities of most enzymes decreased during fermentation with increasing pitching rates.
Keywords: beer composition dehydrogenase enzyme fermentation maltose maltotriose pitching sugar yeast