Effects of recent drought conditions on the Canadian Prairies on the malting quality of barley

Recent droughts

In 2021 and 2023, the Canadian Prairies experienced above average temperatures and varying degrees of drought. In 2022, however, temperatures and precipitation levels were close to average (Figure 1) These conditions allowed us to investigate the effects of high temperature and drought on the grain quality, processing performance, and malt properties of barley by comparing data collected for our annual reports on barley quality in 2021, 2022 and 2023.

Chemical and physical grain characteristics in drought years

High temperatures and drought in 2021 resulted in an average protein content of 13.2% for malting barley, which is significantly higher than the average protein content of 12.3% reported in 2022. Although the 2023 growing season began with high temperatures and below average precipitation, cooler temperatures in July helped relieve crop stress and malting barley from 2023 was found to have the same average protein content as in 2022 (Figure 2). The growing conditions in 2021 and 2023 did, however, produce malting barley with significantly lower test weights and kernel densities, but greater average kernel lengths, compared to 2022 (Figure 2). The latter observation suggests heat and drought may play a role in defining kernel shape. We found that growing conditions did not affect the β-glucan content of malting barley grain, but the average arabinoxylan content was greater in 2021 and 2023 compared to 2022.

Effects of drought on malting qualities of barley

The combination of lower test weight, lower kernel density and elongated kernel shape contributed to the easy and rapid absorption of water during steeping for 2021 and 2023 barley (Figure 3). The occurrence of pre-harvest sprouting in 2021 and 2023, and a lower hardness index in 2023, also helped to decrease hydration time. This resulted in excellent cell wall modification during malting and very low viscosity and concentration of β-glucans in wort (Figure 4). High protein content in grain can reduce malt extract yield and, as expected, the malt made from 2021 barley resulted in the lowest average malt extract level (78.7%) (Figure 4). Despite the protein content of barley in 2022 and 2023 being similar, the malt extract level was lower in 2023 (80.4%) compared to 2022 (81.2%). The lower-than-expected malt extract levels in 2023 barley may be partially due to a slightly lower starch content and lower levels of proteolytic and starch degrading enzymes, especially alpha-amylase, as demonstrated by a lower concentration of soluble proteins and free amino nitrogen.

During malting there is a specific temperature range, referred to as the gelatinization temperature (Tg), at which starch granules lose their crystalline structure and are solubilized. Barley from the 2021 drought had a Tg that was up to 2°C higher than 2022 barley. This increase in Tg can be partly attributed to a higher protein content in barley grown in 2021, stronger starch/protein interactions, and partly to starch properties. We found a strong correlation between the Tg of isolated starches and the Tg of grain, indicating that differences observed in Tg between crop years are due to the physical and molecular characteristics of starches and not just protein content. The isolated starches exhibited a bimodal distribution of large and small granules. Figure 5 shows the variation in Tg and the distribution of small and large starch granules for the variety AAC Connect grown in 2021, 2022 and 2023. The volume of small granules showed a positive correlation with Tg, suggesting that drought conditions may increase the volume of small starch granules, which are known to have a higher Tg than large granules.