Biological Systems Engineering


First Advisor

David D. Jones

Second Advisor

Michael F. Kocher

Date of this Version

Summer 8-13-2021


Mabie, D. M. (2021). Assessment of the Effects of Airflow Conditions Related to Hop Drying. PhD Diss. University of Nebraska-Lincoln


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Engineering, Under the Supervision of Professors David D. Jones and Michael F. Kocher. Lincoln, Nebraska: August, 2021

Copyright © 2021 David M. Mabie


Hops have been utilized by brewers for centuries to contribute bitterness, antimicrobial preservation and desirable aromatic profiles to beer. The hop cone is a small, lightweight, high moisture content flower which produces lupulin glands containing resins and essential oils that contribute desirable characteristics to beer. Due to the high harvest moisture content (75% wet basis), hops must be rapidly dried to properly preserve them for future processing and brewing. While hops have been dried for centuries, most literature from the past century has focused on drying to minimizing loss to the resin or physical cone structure. The objectives of this research were to investigate the relationships between different airflow conditions during drying and the effects to the essential oil content. Research demonstrated that the direction of applied airflow had an effect on the resistance to airflow, resulting in different values for the parameter constants (a and b) in the airflow resistance equation for the design of fan systems during hop drying. Analysis of the relationship between drying air temperature and amount of total essential oils in the dried hops demonstrated a consistent linear decrease in the oils content as the drying air temperature increased. However, results showed no conclusion could be made regarding a relationship between the drying air temperature and the percentage of specific essential oils. The results of this research will aide hop growers’ decision making related to airflow rates, fan selection and drying air temperatures to produce a higher quality hop.

Advisors: David D. Jones, Michael F. Kocher