33. Measurement of Percent Utilization of Hops for Brewing Quality Control Methods

Abstract

Hops are an increasingly important ingredient in today’s beer brewing industry. Hops contains two very different chemical compounds, one being alpha (α) acid, which can isomerize to gives beer a bitter taste, while the other, beta (β) acids, are the contributors to the aroma of a beer. The α-acids are chemically altered when exposed to high temperatures to produce intensely bitter iso-α-acids. With the increase in demand for bitter tasting beers, a technique referred to as whirlpooling has been implemented in many breweries. In this technique copious amounts of hops are added to wort that is at near boiling temperature in hopes to extract large quantities of α-acids to give beer a distinct flavor and aroma profile. As a consequence of the higher contact temperature some extracted α-acids are isomerized to bittering iso-α-acids. In the past, this percent of isomerization has been strictly based on professional tasting panels with no analytical quality control methods in place. It is believed that the hop utilization, or the percent of isomerized α-acids is at near zero, but this seems highly unlikely when considering the temperature is at near boiling when the hops are added. The goal of this work is to use analytical techniques to determine how various factors contribute to the hop utilization using the whirlpool technique. A scaled-down model of the whirlpool was developed and used to study the effects of pH, calcium carbonate, and specific gravity on the formation of α-acid and iso-α-acid quantified by ultraviolet (UV-vis) spectroscopy.