Colloidal examination of worts associated with premature yeast flocculation

This paper reports on a study of the colloidal properties of yeast fermented in control and premature yeast flocculation (PYF) worts. A lager yeast strain was fermented in both control and PYF worts and analyzed for cell wall properties. Yeast from the PYF wort exhibited more flocculation than the control. The PYF fermentation yielded yeast with less negative zeta potential than the control (P < 0.001). When both yeasts were resuspended in beer (filtered through a 10-kDa filter), there was no difference in the surface charge of the control and PYF yeasts (P > 0.05). This suggests that wort colloids or trub larger than 10 kDa caused a reduction in surface charge. Cell separation forces estimated by floc breakup through a capillary indicated PYF yeast flocs exhibited higher apparent separation force. The orthokinetic capture coefficients of control and PYF yeasts showed significant differences in capture coefficient values between both of the yeast suspensions, with the PYF capture coefficient values being higher from 72 hr of fermentation onward (P < 0.05). A physical mechanism of PYF has been proposed that involves electrostatic interaction between wort particles (positively charged toward the end of fermentation) and yeast (negatively charged through fermentation).