Date of Graduation

8-2022

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Threlfall, Renee T.

Committee Member

McWhirt, Amanda L.

Second Committee Member

Lee, Jacquelyn A.

Third Committee Member

Lee, Sun-Ok

Keywords

Alpha acids; chemistry; Humulus; Lupulus; sensory; terroir

Abstract

The hop plant (Humulus lupulus L.) is a perennial, climbing species within the Cannabaceae family that produces cones used for brewing. Hops are grown worldwide. In the United States most hops production occurs in the Pacific Northwest, but growth in the craft beer industry is driving efforts for hops production in other U.S. regions. Recommendations on hops cultivar suitability, fertility, and management are needed for the U.S. mid-south region. Objectives of this research on Arkansas-grown hops were to 1) assess the impact of cultivar and fertility rate on plant and cone attributes of six cultivars of Arkansas-grown hops and 2) determine impact of pruning timing on plant and cone attributes of Arkansas-grown ‘Cascade’. For the first objective, six hop cultivars (Cascade, Cashmere, Centennial, Crystal, Nugget, and Zeus) were planted at the University of Arkansas System Division of Agriculture Fruit Research Station (UA System FRS) in Clarksville, AR in 2018. The six cultivars with three fertility rates (low, standard, and high) were grown in a completely randomized block design consisting of three replicates of three plant plots for each cultivar and fertility treatment combination in 2020 and 2021. Fertility rates consisted of low (97 kg/ha), standard (145 kg/ha), and high (193 kg/ha) rates of Triple 13 (13-13-13) applied in four evenly spilt applications in biweekly intervals on May 15, June 1, June 15, and June 30 of 2020 and 2021. Hops cones were harvested at 70-80% moisture content from August-September 2020 and 2021, dried, packaged, and frozen (-10 °C). Plant, cone, and sensory attributes were evaluated at harvest and compositional attributes of the cones were assessed postharvest. The cultivar x fertility interaction was not significant for any of the plant attributes at harvest while only the immature cone percentage was impacted in 2021. No differences were seen in acid content of the dried hops cones between the fertility rates in 2020, but all acid attributes were impacted in 2021. Cultivar impacted all harvest attributes except number of bines/plant (2.71) and number of nodes/plant (62.70) in both years. The total cone yield for all plants was 26.91% greater in 2020 (31 kg) for 48 plants compared to 2021 (24 kg) which had 45 hop plants that yielded cones. ‘Crystal’ (755.80 g), ‘Cascade’ (983.63 g) ‘Zeus’ (797.58 g), had the highest cone yield/plant while ‘Centennial’ (67.45 g) had the lowest. ‘Crystal’ and ‘Cascade’ had alpha acid levels within standard commercial ranges, while all ‘Zeus’ and ‘Cashmere’ were lower than typical levels. Regardless of year, ‘Cascade’ (5.50%), ‘Cashmere’ (5.41%), and ‘Zeus (4.75%) had the highest total alpha acids while ‘Crystal’ (7.74%), ‘Cascade’ (5.80%), and ‘Cashmere’ (4.91%) had the greatest total beta acids. A trained descriptive sensory panel (n=5-7) evaluated the aroma of dried, ground hops cones and found that aroma of the cones varied by year, and cones harvested in 2021 had a general increase in aromatic intensity, overall impact, and were more distinctive in defined attributes. For objective 2 in 2020 and 2021, ‘Cascade’ hops plants at the UA System FRS were pruned April 15 (Early), April 30 (Mid), or May 15 (Late) by removing all new plant growth from each crown at soil level. There were three replications per pruning timing. The impact of pruning timing and year on plant and cone attributes were evaluated. Pruning timing did not impact any of the plant attributes and most of the cone attributes except the percent of damaged cones/plant with the Mid pruning having the highest damage. Year impacted the number of laterals/plant, total cone yield/plant, and estimated dry cone yield/plant. Total cone yield/plant had a 60.1% reduction in 2021 (421.51 g) compared to 2020 (701.33 g). The ‘Cascade’ hops had total alpha acids (6.28-7.66%) and total beta acids (6.45-9.32%) that were slightly higher than commercially-grown hops. In 2020, the Early pruning had the highest level of alpha and beta acids, while in 2021, the Mid pruning had the highest level. This research indicated that ‘Crystal’, ‘Cascade’, and ‘Zeus’ cultivars have potential for commercial hops production in Arkansas, fertility rate had little to no impact on the measured plant and cone attributes, further pruning timing evaluations are needed to determine best management practices, and cultivar had the most significant impact on plant and cone characteristics.

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