Characterising the cleaning mechanisms of yeast and the implications for Cleaning In Place (CIP)

Deposition of yeast inside brewery process plant is a serious industrial problem. Investigation of the cleaning of beer fermenter deposits revealed two types of fouling; yeast foam (type A) and yeast film (type B). Rheological characterisation indicated both deposits could be mimicked in lab scale fouling experiments using yeast slurry aged for different times. Water and chemical rinsing of these deposits on a lab scale flow cell revealed three distinct cleaning phases: (i) hydration and swelling, (ii) removal in the flow by dissolution and in patches and (iii) no further removal. At 30 and 50 °C water rinsing at the flow velocities investigated could remove up to 85% of the deposit. At a water rinsing temperature of 70 °C, less deposit could be removed overall. Rheological studies indicated that increasing the temperature of the deposit generated a more elastic deposit which may decrease cleanability. Chemical cleaning using 2 wt% Advantis 210 (a NaOH base cleaning agent) eventually gave a visually clean surface at all flow velocities and temperatures. Chemical cleaning at 70 °C gave the shortest cleaning times for all flow velocities, but comparable cleaning times were observed when rinsing at 30 and 50 °C, suggesting that an increase in temperature from 30 to 50 °C might not decrease the cleaning time.

Research highlights▶ Model yeast soils relevant to fermenter operation have been developed. ▶ Water and chemical rinsing of these deposits on a lab scale flow cell revealed three distinct cleaning phases. ▶ At 30 and 50 ̊C water rinsing at the flow velocities investigated could remove up to 85% of the deposit. At 70 ̊C, less deposit could be removed. ▶ Chemical cleaning eventually gave a visually clean surface at all flow velocities and temperatures.