van Nierop Sandra N E, Axcell Barry C, Cantrell Ian C, Rautenbach Marina
Group Brewing Research, SABMiller plc, PO Box 782178, Sandton 2146, South Africa.
Food Microbiol. 2008 Oct;25(7):895-901. doi: 10.1016/j.fm.2008.06.004. Epub 2008 Jun 11.
The brewing of beer involves two major biological systems, namely malted barley (malt) and yeast. Both malt and yeast show natural variation and assessing the impact of differing malts on yeast performance is important in the optimisation of the brewing process. Currently, the brewing industry uses well-established tests to assess malt quality, but these frequently fail to predict malt-associated problem fermentations, such as incomplete fermentations, premature yeast flocculation (PYF) and gushing of the final beer product. Antimicrobial compounds, and in particular antiyeast compounds in malt, may be one of the unknown and unmeasured malt factors leading to problem fermentations. In this study, the adaptation of antimicrobial assays for the determination of antiyeast activity in malt is described. Our adapted assay was able to detect differing antiyeast activities in nine malt samples. For this sample set, malts associated with PYF during fermentation and gushing activity in beer showed high antiyeast activity. Both PYF and gushing are malt quality issues associated with fungal infection of barley in the field which may result in elevated antimicrobial activity in the barley grain. Also, two more malts that passed the normal quality control tests were also observed to have high antiyeast activity and such malts must be considered as suspect. Based on our results, this assay is a useful measure of malt quality as it quantifies the antiyeast activity in malt which may adversely impact on brewery fermentation.
啤酒酿造涉及两个主要生物系统，即麦芽大麦（麦芽）和酵母。麦芽和酵母都存在自然变异，评估不同麦芽对酵母性能的影响对于优化酿造过程很重要。目前，酿造行业使用成熟的测试来评估麦芽质量，但这些测试常常无法预测与麦芽相关的发酵问题，如发酵不完全、酵母过早絮凝（PYF）以及最终啤酒产品喷涌。抗菌化合物，尤其是麦芽中的抗酵母化合物，可能是导致发酵问题的未知且未测量的麦芽因素之一。在本研究中，描述了用于测定麦芽中抗酵母活性的抗菌测定方法的调整。我们调整后的测定方法能够检测九个麦芽样品中不同的抗酵母活性。对于这个样品集，与发酵过程中的PYF以及啤酒喷涌活性相关的麦芽显示出高抗酵母活性。PYF和喷涌都是与田间大麦真菌感染相关的麦芽质量问题，这可能导致大麦籽粒中抗菌活性升高。此外，还观察到另外两种通过常规质量控制测试的麦芽也具有高抗酵母活性，此类麦芽必须被视为可疑麦芽。基于我们的结果，该测定方法是麦芽质量的一种有用度量，因为它量化了麦芽中可能对啤酒厂发酵产生不利影响的抗酵母活性。
