Hydrogen sulphide (H2S) is a colourless, volatile gas that produces a distinctive unpleasant and noxious odour (like rotten eggs or sewage) in wine and beer. H2S is one of the most commonly occurring and persistent problems in wine production. Industry experts estimate that 90% of wine producers will experience problems with H2S or other volatile sulphur compounds, the result being that at least 20% of contaminated wine will require remediation and 2% will be discarded. Although not harmful to human health (given that most escapes in gaseous form), H2S is of great concern to winemakers because it dramatically affects the sensory quality of the end product, sometimes to the point of rendering the wine unsaleable.
H2S is formed as a natural intermediary byproduct of yeast metabolism when sulphates, sulphites and elemental sulphur are consumed by yeast to synthesize sulphur-containing amino acids (e.g., cysteine and methionine). Although one source is the sulphur sprayed onto grapes to control mildew, H2S production can also occur as a result of stuck fermentation, whereby the yeast becomes inactivated before fermentation is complete due to nutrient deficiencies.
Should the production of H2S exceed its consumption by yeast to yield the amino acids, the excess H2S leaks into the end product. This adds to the H2S that already forms in wine from natural degradation of sulphur-containing amino acids. Normally, most H2S vaporizes, along with carbon dioxide, from the wine. However, the minute sensory threshold of H2S means that even the tiniest residual amount can result in a serious problem for the winemaker. Moreover, H2S is quite reactive, and other volatile sulphur compounds may further develop from chemical modification of H2S.
Despite best efforts to address the problem, remediation of H2S (e.g., treatment with copper sulphate) also typically taints and compromises the resulting wine product. Addressing one contaminant by adding another has other complicating and undesirable ramifications.
One example was the 2007 rejection of 4,000 cases of a New Zealand pinot noir by its German buyer after the discovery that the wine's copper content exceeded European standards for heavy metal content (copper is used to counteract the H2S). Reports indicate that the New Zealand wine company subsequently decided to sell the affected wine at various supermarkets under a different brand name, and at prices marked down by more than half. H2S can exact a significant revenue cost to commercial wineries.
Functional Technologies' H2S-preventing wine yeasts were launched commercially in 2010 and enjoyed significant initial interest and response from the winemaking industry with 75 wineries in 13 U.S. states placing orders for the 2010 crush. In 2011, the company's distributor increased its minimum purchase volume by more than 350%, an indicator of positive wine industry response. Functional Technologies is continuing to expand it sales effort by augmenting the distributor effort with a direct sales program and an expansion of sales into European and South American markets.