The designation of Oud Bruin exists in East and West Flanders, Belgium and the Netherlands. In the Netherlands, Oud Bruin is a sweet beer that is low in alcohol. In East and West Flanders, however, it is a sour beer. In East Flanders, Oud Bruin is fermented with yeast and Lactobacillus and then matured in steel tanks. In West Flanders, however, the beer is fermented with yeast and Lactobacillus and then aged in wooden casks for up to 24 months. This is the last stage at which the beer is infected with Brettanomyces cultures. Oud Bruin from West Flanders often has a dominantly sour flavour, but the beers differ widely from one brewery to the other. In West Flanders Oud Bruin, the sour flavours are often complemented by touches of oxidation due to the long barrel aging process, which reminds the connoisseur of Madeira or Sherry wine flavours. Oud Bruin is dark brown (East Flanders) to burgundy red in colour (West Flanders). Oud Bruin interpretations can be characterised by a strong malty flavour and fruity ester components. Hoppy flavours are insignificant. The addition of sugar frequently results in a higher alcohol content, while retaining the subtle tartness. An impressive beer among the West Flanders Oud Bruins, also referred to as Vlaams Rood or Flanders Red Ale, is Duchesse de Bourgogne – one of the favourites of the author of this article.