Behavior of Geranic Acid and Related Compounds during Hop (Humulus lupulus L.) Cone Maturation: Comparison among Sorachi Ace, Its Daughters, and Other Hop Varieties.

Abstract

Numerous hop varieties with unique aromas─flavor hops─have been developed to enhance beer flavor. Sorachi Ace (bred by Sapporo Breweries Ltd.) is the mother of several characteristic flavor hop varieties including Hokuto Ace and Furano Special. Our previous research found significant levels of geranic acid in Sorachi Ace hops and beers. Owing to its acidic nature, this compound remains abundant throughout the brewing process, including wort boiling and fermentation. Moreover, when geranic acid is combined with other hop-derived compounds, it contributes to the characteristic varietal aroma of Sorachi Ace beers. This study investigated the behavior of geraniol-related compounds (geraniol, geranial, geranic acid, and methyl geranate) during extended harvest periods in eight hop varieties, including Sorachi Ace and its daughters. Hops were harvested at different days after flowering (DAF): from 45 DAF (normal harvest) to 85 DAF. Hokuto Ace and Furano Special displayed lower geranic acid levels than Sorachi Ace, although its geranic acid-accumulation trait was more or less inherited. The conversion of geranic acid to methyl geranate progressed in most hop varieties, except for Sorachi Ace and its daughters. In these varieties, esterification was strongly suppressed, especially in Sorachi Ace and Hokuto Ace, leading to geranic acid accumulation with extended harvest time. These results support a geranic acid accumulation mechanism in these varieties. In Cascade, Columbus, and Magnum hops, geranic acid was scarcely detected, whereas geraniol, geranial, and methyl geranate levels increased from 45 DAF to 65 DAF. Conversely, in Sorachi Ace and its daughter hops, geraniol and geranial levels gradually decreased with extended harvest, suggesting that geranic acid accumulation may suppress the biosynthesis of these compounds.