NIZO, Department of Process Engineering, P.O. Box 20, 6710 BA Ede, The Netherlands.
Biotechnol Bioeng. 1997 Oct 20;56(2):190-200. doi: 10.1002/(SICI)1097-0290(19971020)56:2<190::AID-BIT8>3.0.CO;2-K.
Quantification of yeast flocculation under defined conditions will help to understand the physical mechanisms of the flocculation process used in beer fermentation. Flocculation was quantified by measuring the size of yeast flocs and the number of single cells. For this purpose, a method to measure floc size and number of single cells in situ was developed. In this way, it was possible to quantify the actual flocculation during fermentation, without influencing flocculation. The effects of three physical parameters, floc strength, fluid shear, and yeast cell concentration, on flocculation during beer fermentation, were examined. Increasing floc strength results in larger flocs and lower numbers of single cells. If the fluid shear is increased, the size of the flocs decreases, and the number of single cells remains constant at approximately 10% of the total cells present. The cell concentration also influences flocculation, a reduction of 50% in cell concentration leads to a decrease of about 25% in floc size. The number of single cells decreases in linear proportion to the cell concentration. This means that, during yeast settling at full scale, the number of single cells decreases. The results of this study are used in a model for yeast flocculation. With respect to full scale fermentation the effect of cell concentration will play an important role, for flocculation and sedimentation will occur simultaneously leading to a quasi steady state between these phenomena. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 190-200, 1997.
在规定条件下定量酵母絮凝有助于理解啤酒发酵中使用的絮凝过程的物理机制。通过测量酵母絮体的大小和单个细胞的数量来定量絮凝。为此，开发了一种原位测量絮体大小和单个细胞数量的方法。通过这种方式，可以在不影响絮凝的情况下定量发酵过程中的实际絮凝。研究了三个物理参数，絮凝强度、流体剪切和酵母细胞浓度，对啤酒发酵中絮凝的影响。增加絮凝强度会导致更大的絮体和更少的单个细胞。如果增加流体剪切，絮体的大小会减小，而单个细胞的数量在大约 10%的总细胞存在时保持不变。细胞浓度也会影响絮凝，细胞浓度降低 50%会导致絮体大小降低约 25%。单个细胞的数量与细胞浓度成线性比例减少。这意味着，在全规模酵母沉降过程中，单个细胞的数量减少。本研究的结果用于酵母絮凝模型。对于全规模发酵，细胞浓度的影响将起着重要作用，因为絮凝和沉淀会同时发生，导致这两种现象之间存在准稳态。（c）1997 年 John Wiley & Sons，Inc. 《生物技术与生物工程》56:190-200,1997。
