Verbelen P J, Dekoninck T M L, Saerens S M G, Van Mulders S E, Thevelein J M, Delvaux F R
Centre for Malting and Brewing Science, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, P.O. Box 2463, 3001, Heverlee, Belgium.
Appl Microbiol Biotechnol. 2009 Feb;82(1):155-67. doi: 10.1007/s00253-008-1779-5. Epub 2008 Nov 19.
The volumetric productivity of the beer fermentation process can be increased by using a higher pitching rate (i.e. higher inoculum size). However, the impact of the pitching rate on crucial fermentation and beer quality parameters has never been assessed systematically. In this study, five pitching rates were applied to lab-scale fermentations to investigate its impact on the yeast physiology and beer quality. The fermentation rate increased significantly and the net yeast growth was lowered with increasing pitching rate, without affecting significantly the viability and the vitality of the yeast population. The build-up of unsaturated fatty acids in the initial phase of the fermentation was repressed when higher yeast concentrations were pitched. The expression levels of the genes HSP104 and HSP12 and the concentration of trehalose were higher with increased pitching rates, suggesting a moderate exposure to stress in case of higher cell concentrations. The influence of pitching rate on aroma compound production was rather limited, with the exception of total diacetyl levels, which strongly increased with the pitching rate. These results demonstrate that most aspects of the yeast physiology and flavour balance are not significantly or negatively affected when the pitching rate is changed. However, further research is needed to fully optimise the conditions for brewing beer with high cell density populations.
通过采用更高的接种率（即更大的接种量），可以提高啤酒发酵过程的体积产率。然而，接种率对关键发酵和啤酒质量参数的影响从未得到系统评估。在本研究中，将五种接种率应用于实验室规模的发酵，以研究其对酵母生理学和啤酒质量的影响。随着接种率的增加，发酵速率显著提高，酵母净生长量降低，但对酵母群体的活力和生命力没有显著影响。当接种较高酵母浓度时，发酵初始阶段不饱和脂肪酸的积累受到抑制。随着接种率的增加，HSP104和HSP12基因的表达水平以及海藻糖浓度升高，这表明在细胞浓度较高的情况下酵母受到适度的应激。接种率对香气化合物产生的影响相当有限，但总双乙酰水平除外，其随接种率强烈增加。这些结果表明，当接种率改变时，酵母生理学和风味平衡的大多数方面不会受到显著或负面影响。然而，需要进一步研究以充分优化高细胞密度群体酿造啤酒的条件。
