Two Decades of “Horse Sweat” Taint and Brettanomyces Yeasts in Wine: Where do We Stand Now?

Abstract

The unwanted modification of wine sensory attributes by yeasts of the species Brettanomyces bruxellensis due to the production of volatile phenols is presently the main microbiological threat to red wine quality. The effects of ethylphenols and other metabolites on wine flavor is now recognized worldwide and the object of lively debate. The focus of this review is to provide an update of the present knowledge and practice on the prevention of this problem in the wine industry. Brettanomyces bruxellensis, or its teleomorph, Dekkera bruxellensis, are rarely found in the natural environment and, although frequently isolated from fermenting substrates, their numbers are relatively low when compared with other fermenting species. Despite this rarity, they have long been studied for their unusual metabolical features (e.g., the Custers effect). Rising interest over the last decades is mostly due to volatile phenol production affecting high quality red wines worldwide. The challenges have been dealt with together by researchers and winemakers in an effective way and this has enabled a state where, presently, knowledge and prevention of the problem at the winery level is readily accessible. Today, the main issues have shifted from technological to sensory science concerning the effects of metabolites other than ethylphenols and the over estimation of the detrimental impact by ethylphenols on flavor. Hopefully, these questions will continue to be tackled together by science and industry for the benefit of wine enjoyment.

Novel analytical approach to assess the profile of volatile phenols in Portuguese red wines

“…Barrel maturation adds more complexity to wine as wood leaches strong odorant chemicals, namely, volatile phenols, eugenol and vanillin. All can be present in barrel‐aged wines at a concentration above their preference threshold because traditional wooden vats are typical niches of B. bruxellensis (Prida and Chatonnet , Malfeito‐Ferreira ). These yeasts have a vinylphenol reductase that converts the vinylphenols into the respective ethylphenol; however, it would be expected that wines aged in wood barrels would have a higher concentration of ethylphenols and wines not aged in wood barrels a higher concentration of vinylphenols (Nikfardjam and Tschiersch ).…”

“…Even though wood barriques may not be the source of the yeasts, they are readily contaminated if filled with tainted wine. In contrast, high‐ethanol wines (>17%, v/v), such as sherry or Port wines, are not vulnerable to these yeasts even when aged in old wooden vats (Malfeito‐Ferreira ). In this study, there were insufficient data to conclude about the influence of the vessel's material or the alcohol concentration on the concentration of volatile phenols.…”

“…It is described by tasters as a ‘horse‐sweat’ aroma, and contamination leads to large economic losses on the grounds that, once established in a winery, this yeast genus is difficult to eliminate, even after the exogenous addition of sulfites, and it has a negative impact on varietal and typical aroma characteristics (Steensels et al ). Currently, this species is seen as the main threat posed by yeast to wine quality (Malfeito‐Ferreira ).…”

An important step forward for the future development of an easy and fast procedure for identifying the most dangerous wine spoilage yeast,Dekkera bruxellensis,in wine environment

“…Beneficial and spoilage microorganisms can act during the winemaking process. Dekkera bruxellensis (or its anamorph Brettanomyces bruxellensis) is considered a major cause of wine spoilage worldwide (Fugelsang, 1997;Loureiro and Malfeito-Ferreira, 2003;Malfeito-Ferreira, 2018) since it confers undesirable phenolic flavours and odours to wine (Chatonnet et al, 1992(Chatonnet et al, , 1993(Chatonnet et al, , 1995(Chatonnet et al, , 1997Fugelsang, 1997;Loureiro and Malfeito-Ferreira, 2003). Therefore, it is crucial for the wine industry to detect and identify D. bruxellensis before wine degradation in a fast and accurate way to prevent large economic losses.…”

Beverage Sensory Modification

“…Under a different scope, off-flavors also deserve the attention of researchers. For instance, the world-famous Chardonnay from Burgundy may be affected by oxidative notes that indicate premature aging [7] The highly debated "horse sweat" taint was also reviewed, encompassing technical preventive measures and the influence of volatile phenols on sensory attributes [8].…”