Nitrogen and sulfur fertility practices: Influences on hop chemistry, aroma, and nitrate accumulation

Authors: Gent, David - Dave; BLOCK, MARY - Oregon State University; MASSIE, STEPHEN - Washington Hop Commission; Phillips, Claire; RICHARDSON, BRIANA - Oregon State University; SHELLHAMMER, THOMAS - Oregon State University; Trippe, Kristin; WISEMAN, MICHELE - Oregon State University

Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2023
Publication Date: 5/18/2023
Citation: Gent, D.H., Block, M., Massie, S.T., Phillips, C.L., Richardson, B.J., Shellhammer, T.H., Trippe, K.M., Wiseman, M.S. 2023. Nitrogen and sulfur fertility practices: Influences on hop chemistry, aroma, and nitrate accumulation. Journal of the American Society of Brewing Chemists. https://doi.org/10.1080/03610470.2023.2204412.
DOI: https://doi.org/10.1080/03610470.2023.2204412

Interpretive Summary: Hops are an essential component of brewing used to impart flavor, aroma, and bitterness to beer. Production practices such as fertilization during hop growing can impact aspects of hop quality. One quality attribute of potential importance is the nitrate concentration in hops because nitrate transfers at high rates into beer during brewing, potentially resulting in elevated nitrate levels in the finished beer depending on hopping rate. In this research, we evaluated how nitrogen and sulfur fertilization practices jointly influence hop yield, brewing chemistry, and the aroma of hops and beer. We found that in Washington State, increasing the dose of sulfur fertilization reduced nitrate levels in hop cones at harvest without negatively affecting yield, hop brewing chemistry, aroma, or a suite of potent flavor compounds in hops. However, this effect was study-dependent and we observed no response in related studies in Oregon when sulfur dose was increased over an 11-fold range. In summary, this research indicates that in certain situations growers may be able to reduce nitrogen fertilization by increasing sulfur fertilization, which can reduce nitrate levels in hops without sacrificing crop yield or quality.

Technical Abstract: In multiple plant species, sulfur and nitrate have an antagonistic relationship such that higher sulfur concentrations in foliage correspond with lower nitrate concentrations. We investigated the potential for managing sulfur fertilization as a means to reduce nitrate levels in hops, and how nitrogen and sulfur fertilizer dose jointly affect hop yield, brewing chemistry, and aroma of hops and beer. In an observational study of commercial lots, we found a weak positive correlation between sulfur and nitrate concentrations. In a controlled study in a Simcoe® hop yard in Washington, a factorial combination of representative low and high rates of nitrogen and sulfur fertilizer revealed that nitrate content of cones increased 13 to 22% with the high nitrogen dose, yet declined 8 to 8.7% with the high sulfur dose. Yield was unaffected by the lower dose of nitrogen when sulfur dose was high. Treatment effects on a-acids, total oil content, and hop and beer aroma were not detected. Levels of the thiol precursor cysteine-3SH and cytseinylglycine-3SH were reduced 19% and 23%, respectively, in cones that received the higher sulfur dose in one year; other thiols and precursors were unaffected. A controlled field study with cultivar Willamette in Oregon found that increasing sulfur dose over an 11-fold range by varying nitrogen fertilizer form from urea to ammonium sulfate had non-detectable or only small effects on yield, a-acids, or nitrate concentrations. Hop aroma and brewing characteristics appear largely invariant to sulfur fertilization practices, although increased sulfur fertilization may reduce nitrate levels modestly in cones in certain situations.