Fermentability of Canadian two row malting barley varieties: Wort turbidity, density, and sugar content as measures of fermentation potential

Chris J Bourque, Dalhousie University, Halifax, Nova Scotia, Canada
Co-author(s): Alex Speers Dalhousie University, Halifax, NS, Canada

ABSTRACT: There has been little research conducted on the relative fermentability of Canadian barley malt varieties, despite their putative high enzyme content, which suggests high fermentation potential. The primary goal of this study was to investigate and compare the fermentation performance of malt produced from 11 Canadian two-row barley varieties grown during the 2008 and 2009 crop seasons. Thus, 22 samples were analyzed. Common malting varieties tested included Harrington (a de facto “gold standard”), AC Metcalfe, CDC Copeland, and CDC Kendall, while feed varieties CDC Dolly and CDC Bold provided a negative fermentability control. Less common malting varieties, CDC Helgason and McLeod, were also tested. As well, three experimental varieties (TR251, TR306, and BM9752D-17) were included in this study due to their varied display of enzymatic activity; of chief interest was the amylase thermal stability exhibited by each, and its effect on attenuation. Fermentation was carried out using a miniaturized fermentation assay consisting of 33 test tubes, each with 15 mL of wort, allowing triplicate measurement at 0, 1, 6, 22, 26, 30, 46, 50, 54, 70, 74, and 78 hr throughout fermentation. Wort was pitched to an initial concentration of 1.5 × 107 cells/mL using SMA yeast, and test tubes submerged in a water bath at a constant temperature of 21°C. Apparent extract (AE) and absorbance were measured using a digital density meter and spectrophotometer (600 nm), respectively, and samples were collected for carbohydrate and ethanol HPLC analysis at each time interval. Wort attenuation, including AE and calculated real extract (RE), carbohydrate consumption, and ethanol production, were modeled using the logistic equation. Global F tests were performed between each variety and the standard Harrington, and parameters of RE and fermentable carbohydrates were analyzed using two-way analysis of variance and step-wise multiple linear regression. Results indicate that all but the feed varieties fermented well, achieving low final attenuation and exhibiting similar fermentation characteristics. Despite only minor performance differences among the top fermentors, it was found that between crop seasons both AC Metcalfe and CDC Copeland fermented as well or better than Harrington, as measured by their respective apparent degree of fermentation (ADF). Harrington displayed substantial performance variation between seasons, reaching an ADF of 0.88 in 2007 and only 0.83 in 2008. BM9752D-17 fermented consistently between years, displaying enhanced fermentation to that of Harrington in 2008. HPLC and kinetic analysis of sugar consumption throughout fermentation confirmed that fermentable carbohydrates are consumed in an orderly and overlapping manner. The rate of fermentable sugar consumption (glucose, maltose, maltotriose, and fructose) was successfully modeled with the logistic equation. It was found that initial glucose levels positively affected the rate of sugar consumption at the midpoint of the fermentations. Two-way ANOVA of all logistic parameters for RE and fermentable carbohydrates revealed the majority of fermentation variation resulted from inherent differences between varieties rather than seasonal variation.

Chris Bourque received a B.S. degree with first-class honors in human kinetics and health science from St. Francis Xavier University, Antigonish, NS, Canada. He pursued further education in the Department of Microbiology and Immunology before starting work on an M.S. degree in brewing science at Dalhousie University, Halifax, NS, Canada, in January 2010. He expects to defend his dissertation in May 2012.