Determination of Hop Alpha Acids and Hop Acid Utilization From Whirlpool Brewing Processes Using a Scaled-down Industrial Method and High Performance Liquid Chromatography

Abstract

Hops are the female seed cones or flowers of the hop plant, humulus lupulus and contain chemical compounds, known as alpha (α) and beta (β) acids, which contribute to the bitterness, aroma, stability, and other final characteristics of beer. Nearly every commercial beer uses hops as the exclusive spice for flavoring. Three similar chemical varieties of α-acids (humulone, cohumulone, and adhumulone) are generally chemically rearranged when exposed to high temperatures during boiling to produce intensely bitter iso-α-acids. The β-acids (lupulone, colupulone, and adlupulone) and some unaltered α-acids are the main contributors to the aroma of the beer. Since hops are an important factor in the overall bitterness and aroma of beer, it is important to know the concentration of α-acids and the extent to which they will be chemically altered to the very bitter iso-α-acids (known as % utilization). There are a multitude of hops distributors worldwide (Hopunion, US organic hops, etc) that offer varieties of hops with various known concentrations of α-acids and β-acids. This information gives the brewer a very general understanding of the amount of hops to use, when to add the hops to the wort (unfermented beer), and the length of time the hops should be exposed to high temperatures to induce the chemical change to iso-α-acids. Commercial brewers are also recently applying a technique called whirlpooling to separate undesirable solids from the wort before fermenting the beer. For some styles of beer, copious amounts of hops are added to the whirlpool while the wort is still hot. This results in increased hop contact times with the heated wort (upwards of 60 min). It is generally assumed that hop utilization (% α-acids converted to iso-α-acids) from this technique is near zero, but this is highly unlikely and the brewing industry does not always have analytical quality control methods to make these determinations. To date, the only attempts to determine hop utilization from whilrpooling have been highly subjective, utilizing professional tasting panels rather than actual detection of α- and β- acids and iso-acids. The initial goal of this work is to use a characterization technique called High Performance Liquid Chromatography (HPLC) to quantify the hop acid content and determine how various whirlpool process factors will affect hop utilization.