Wort Boil Time and Trub Effects on Fermentability

Abstract

The purpose of this research was to understand and evaluate the effect of high temperature treatment of wort at varying time periods (30, 45, 60, 90, and 120 min) on wort fermentability. The effect of trub was also analyzed. Small-scale fermentations were conducted using a malt (malted from AC Metcalfe) free of premature yeast flocculation tendencies and a standard SMA yeast strain. The turbidity and apparent extract were measured at specific time intervals. The decline in extract was modeled with the ASBC Yeast-14 logistic equation predicting a sigmoidal curve. Turbidity measurements were modeled with a “tilted Gaussian” fit. Heat-treating the wort (at 100 or 121.1 °C) resulted in a significant decline in ADF (p < 0.05). As denoted by the midpoint of the fermentation, all fermentation runs, with and without trub, at lower wort boil durations fermented faster than longer or higher wort-boiling treatments. The decline in wort fermentability was highest upon treatment at wort temperature and pressure levels of 121.1 °C and 3.0 atm. The amount of trub and the wort color formed after each heat treatment showed a gradual increase with heating duration. Free amino nitrogen levels of wort declined significantly with respect to both increase in wort boiling temperature and time intervals (p < 0.001).