By Nick Race, Mudbrick Cellar Door Team.

Have you ever opened an bottle of old red wine and been confronted with a terrible smell? Chances are that it has been infected by Brettanomyces.

Wine is such an amazing drink; made from nothing but grapes and yeast, it can take on an infinite diversity of flavours and aromas. It reflects the place it comes from, the climate from a particular year and the winemaking process. As they say, it’s all about the “terroir” that defines the wine.

Describing a wine has always been difficult; it’s such a personal thing, relying on your association with past experiences. Experts have tried to quantify the aroma and taste in an analytical way and come up with an aroma wheel with a set of terms which attempt to describe the wine. The wine scientists have then tried to find the specific chemical which produce those aromas.

So back to that terrible smell; some wines have “off-odours” which are classified as wine faults. The odour I want to discuss today smells like “barnyard”, “sweaty saddle”, “Band-Aid”, “medicinal” and even “horse”. It is caused by a set of chemicals known as ethyl-phenols which only occur in red wine and are produced by a yeast called Brettanomyces bruxellensis.

Affectionately known as “Brett”, these aromas can enhance a wine in mild form but quickly become unpleasant in larger concentrations. Brettanomyces is present in all stages of winemaking, and can survive both the alcoholic and malolactic fermentation processes, but does it’s the most damage during barrel aging as it can live in the grains of the wood.

In previous centuries, winemakers were unaware of micro-organisms and the need for sterilization to prevent contamination, so Brett became a characteristic of wines from the ‘old world’ (sometimes called “French pong”). Nowadays, modern winemakers are meticulous about hygiene and use antimicrobial techniques as well as sterile filtration to ensure these yeasts are removed from the final wine, so hopefully those terrible smells will become a thing of the past.