The fabulous world of bretts
Bretts, the abbreviation of brettanomyces, are 'secondary' yeasts that come into play when the 'primary' ones, saccharomyces, for some reason have not properly fulfilled their function during fermentation. Why does this happen and, above all, what does this mean? It happens when saccharomyces cause the concentration of alcohol to be excessive, in other words when there is too much sugar in the grapes. This is one of the reasons why Bretts are evident in many southern wines or those produced in particularly hot years. It also happens when, under conditions that are not ideal, indigenous or natural yeasts do not function properly or when the level of sulfur dioxide is too low to contrast the Bretts. What do Bretts do to a wine? Basically they produce odors that are not exactly welcome, acceptable only in small does when they become part of a wine's character, as in Mediterranean wines and those from the south in general. When they are excessive they can be very unpleasant. The odor is that of organic waste, if we wish to be polite, or as the more blunt French would say merde de poul. These odors can sometimes be confused with those of harmless reductions which, as opposed to those caused by Bretts, can be resolved through a little breathing. Some lesser experienced tasters fall into this trap and are a little too quick to opt for the worst case scenario in judging a wine.
It is important to know certain things about Bretts. The first is that they are an enemy of the so-called 'natural' or organic wines and thus need to be taken into account when choosing wine-making methods that respect the environment or bring out typical characteristics of wines. The second is that it is is almost inevitable to have some Bretts and, as I said earlier, when they are only in the background they can represent an element of a wine's complexity and thus would not necessarily be considered a defect. The third consideration is that great care is always needed because Bretts are invasive and can spread through cellars and barrels, especially when cleanliness is lacking, and then the problem becomes a very big one because the various methods for eliminating them are complicated and expensive and can even block production for several years.