Aroma Profile of Hops, Humulus Iupulus, as a Function of Boil Time

Introduction

Hops, Humulus lupulus, are one of the primary ingredients in beer and serve as both a natural preservative and as a flavoring agent. These leafy green flowers, shown in Figure 1, are responsible for the characteristic bitterness in beer, but can also impart other flavors such as floral, tangy, piney, or citrusy notes. One factor that impacts the eventual flavor profile of beer is the selection of hop variety, as different strains lead to different flavors and aromas. Another important aspect is the timing of the hop addition during beer brewing. Brewing is a multi-step process that begins by mixing grains with hot water to convert starches in the grain to a sugary solution called wort. The wort is filtered and then boiled together with hops and other specialty ingredients to further develop flavors. At the completion of the boil, yeast is added to initiate fermentation. Hops can be added at any point during or after the boil to bring out desired flavors. Generally, hops are added earlier to draw out bitterness and later to highlight aroma and flavor.