Construction and Demonstration of a Standardized Hop Boiled Water Extraction Method and its Application for a Sensory Evaluation System of Hop Aroma Characteristics

Abstract

Hops impart characteristic flavors to beer. The key hop aroma compounds contributing to beer flavor have been intensively identified and studied; however, sensory evaluation remains necessary to evaluate hop aromas. High-throughput evaluation is vital, especially for preliminary hop seedling selection in breeding programs. Most of the volatile essential oils in hops are significantly evaporated during the wort boiling process after hop dosing. Furthermore, the compositions of essential oils in the boiled wort are changed from the original compositions in the hops as a result of the chemical and physical properties of the volatile aroma components, such as hydrophobicity and volatility. The so-called hop tea method is conducted to facilitate hop development but has not yet been scientifically discussed. In this study, we propose a sensory evaluation system of hop aromas based on the standardized hop boiled water (HBW) extraction method, in which hops are dosed to an α-acid level of 0.5 g/L in distilled water in glass flasks and autoclaved. Descriptive sensory evaluation was applied for the HBW samples, and nine descriptors were established for HBW evaluation. The results indicated that HBW extraction provided a good simulation of late-hopping in the wort boiling process. The aroma characteristics of hop varieties, even those harvested in different crop years, could be characterized by the sensory evaluation system. Moreover, the flavor hops were discriminated from the other categories of hop varieties (aroma hops and bitter hops). Consequently, the HBW method and sensory evaluation system proposed in this report allow for a high-throughput evaluation of hop cone samples suitable for the selection of new flavor hops.