Display Title

A comparison of small-scale fermentability assays to industrial-scale fermentations

Malt barley breeders and maltsters often strive to improve the quality of their product by selecting for and/or manipulating the fermentability of their malt. The fermentability of novel malt barley varieties is the most important characteristic for acceptance of the grain by industry. Small-scale assays are often used to assess the fermentability of malt; however, it is unclear how these trials correlate with industrial processes. This uncertainty may allow poor genetics to be propagated by malt barley breeders or promising varieties to be rejected by industry. There are several factors that likely contribute to discrepancies in fermentability such as pitching rate, mashing regime, fermentation temperature, barley modification, and batch size. This study aimed to isolate and examine the effects of fermenter size on brewing by undertaking small-scale (15 and 200 mL) assays in parallel to industrial fermentations. Using wort supplied by local breweries, miniature fermentations were conducted in parallel to their industrial counterparts. Samples were taken from each fermentation vessel at regular intervals throughout the fermentation. Turbidity was assessed spectrophotometrically at 600 nm and specific gravity was measured using a portable densitometer. It was found that fermentation size had an affect on the apparent degree of fermentation for larger breweries, but not for smaller operations. The discrepancy observed was consistent for each brewery. For example, a large difference of 1.1°P ± 0.2°P was observed between the final gravities of a 20-hL brewery and a 15-mL assay over three consecutive experiments. However, when the wort from an 8.5-hL microbrewery was tested using the small assay, no statistical differences in final gravity were found. During these trials, the turbidity trends were identical; however, the absorbance of the small-scale assay was consistently lower. It was hypothesized that the increased shear generated within the larger scale fermentors maintained the yeast in suspension longer, thereby affecting the final gravity. The shear generated through consumption of sugar and subsequent production of carbon dioxide was theoretically determined for each fermentor. The reduced shear generated within the shorter fermentors likely influenced the yeast floc distributions and subsequent final gravity. To properly make use of small-scale assays, a size correlation was proposed to rationalize the effect of fermentor size on fermentations. Work is currently ongoing to further quantify and control the variables that influence observed discrepancies between small-scale assays and industrial fermentations.

Andrew J. MacIntosh was awarded a diploma of engineering from Saint Mary’s University (Nova Scotia, Canada) and a B.Eng. degree in biological engineering from Dalhousie University (Nova Scotia). After working in industry for several years, he took the opportunity to complete an MAS degree in biological engineering and is now pursuing a doctorate degree in the applied field of food science. Andrew is currently completing the 5-year engineer-in-training apprenticeship to achieve the status of professional engineer. In addition to ASBC, Andrew is also a member of the American society of Biological Engineers and regularly serves on the council of the Dalhousie Engineering Graduate Society. When not conducting research, Andrew is an avid home brewer. His background has contributed to many successful experimental brews, in addition to the odd catastrophe.