Effects of fermentation parameters and cell wall properties on yeast flocculation

Fermentations of industrial wort were conducted in tall tube fermenters with an ale brewing yeast strain (LCC125). The effects of various fermentation parameters and cell wall properties on flocculation of LCC125 were studied during 120 h of fermentation. Evaluation of changes in cell volume during fermentation revealed a non-normal distribution (P < 0.05) at most fermentation times. The mean cell volume initially decreased in the first 24 h of fermentation then peaked over 24--60 h. Cell volume then declined until the end of fermentation. While yeast flocculation began after 24 h, most flocs remained in suspension until 60 h when shear rate due to CO2 evolution declined to below 8 s-1. Both Helm's flocculence and cell surface hydrophobicity rapidly increased to high and stable values from 24 h onward. The yeast cells were essentially flocculent and prepared to flocculate at all times during fermentation. The carbohydrate ligand and zymolectin density did not significantly change with fermentation time (P > 0.05). The flocculation properties of suspended and settled yeast cells were not found significantly different (P > 0.05). Orthokinetic capture coefficient (alpha0) of LCC125 significantly increased (P < 0.001) after 24 h of fermentation, when glucose and maltose in wort depleted. Addition of glucose or maltose significantly inhibited (P < 0.01) orthokinetic flocculation of LCC125. Results of this study indicate that fermentable sugars such as glucose and maltose and shear forces exerted major influences on yeast flocculation during beer fermentation.