HYDROGEN SULFIDE IN BEER AND WINE
Summer is here. And what activity better exemplifies summer than sitting by the pool, taking in the sun’s bounty, and enjoying an ice cold beer? However, if that beer smells faintly of rotten eggs or has a dreaded “skunky” flavor it can ruin an otherwise idyllic afternoon.
So what causes these undesirable off flavors? During fermentation the yeast which converts simple sugars into alcohol also naturally produce some hydrogen sulfide (H2S). Low levels of H2S are actually desirable and give the beer complex, defining flavor characteristics. However at higher concentrations H2S is responsible for the off-putting rotten egg smell, and the interaction of H2S with the hops used in the brewing process are responsible for the skunky odor in bad beer. Excess H2S can be a symptom of unhealthy yeast, microbial infection, improper oxygen levels during fermentation, or a myriad of other root causes.
Due to the volatility of H2S (b.p. = -60°C), one effective method for testing the concentration of dissolved H2S is to test the headspace above the liquid. If the temperature and accumulation time are well controlled, then the concentration of H2S in the headspace will be proportional to the concentration of H2S dissolved in the sample. Brewers have sophisticated sensors in their fermentation tanks to monitor the H2S concentration during production, but as anyone who has bought an off case of beer knows, bad beer can sometimes make it into the bottle.
Figure 1: Apparatus Setup for determination of H2S in beer by Jerome®J605
Arizona Instrument LLC has a solution for the determination of H2S in bottled beer using the Jerome® J605 Hydrogen Sulfide Analyzer. The method can be run in under seven minutes and can be used to determine H2S concentration in beer as low as 5 parts per billion (ppb). No hazardous materials are required for testing. The instrument response over the range investigated was linear with respect to concentration.
To run a test, an Erlenmeyer vacuum flask is connected to a Jerome® J605 Hydrogen Sulfide Analyzer by tygon or other suitably sized inert tubing. A full bottle of beer is poured into an Erlenmeyer flask and allowed to stir for 5 minutes. The instrument is placed in auto range and auto sample, sampling the head-space above the beer every 2 minutes. The instrument is allowed to sample for 30 minutes, and the results are then summed.
James A. Moore, Garrett M. Rowe