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104 { THE SOMM JOURNAL } JUNE/JULY 2014 How It Happens, and Why It Is Increasing So what causes this problem? There's a misconception that brett con- tamination is solely a hallmark of wineries with poor hygiene. "Brett can occur in the cleanest cellars," says New Zealand winemaker Matt Thomson, who is an expert on the subject. It has been identified in every wine region where people have looked for it. Thomson thinks that oak is largely to blame for many infections, because brett can live in the oak and it is almost impossible to get out by cleaning. "If you use new oak, you will get brett: It is not something you can associate just with a dirty cellar." Brett particularly likes toasted new barrels, and has been found eight millimeters deep in staves. This makes it very hard to remove by steam or ozone cleaning. It can feed off a compound, cellobiose, formed when barrels are toasted. Thomson goes further, suggesting that brett is not only associated with new oak, but also that he has identified specific coopers who have a problem with bretty barrels. Brett is also associated with old barrels. Because it is such a resilient yeast, it will survive most cleaning attempts. What can be done to avoid brett, according to Thomson? This is where things get interesting, because many of the steps that need to be taken in order to ensure clean wines run counter to the sort of winemak- ing approach you'd want to take to make interesting wines. The first is to avoid barrels. Stainless steel can be cleaned properly, which vastly reduces the risk. Second, you need to avoid cross-contam- ination. When taking barrel samples Thomson uses plastic barrel thiefs that are used just once, and then sterilized. He also avoids doing rack and return where the wine would go from several barrels to be mixed up in one tank: instead, each barrel is racked separately to tank and returned, and the tank cleaned before the procedure is repeated with the next barrel. The next stage is to keep pH low, either by acidifying or harvesting earlier. This is crucial in the fight against brett. Because brett is wide- spread, make your wine an uninviting habitat for its growth. If you make your wine in the sort of place where brett is happy growing, it will. Low pH is important for two reasons. First, brett doesn't like more acidic media. Second, at lower pH any sulphur dioxide (SO 2 ) additions will be much more effective, and more of the SO 2 will be in the active (molecu- lar) form. Another important prevention measure is to keep the time from the end of alcoholic fermentation to the end of malolactic fermentation as short as possible. SO 2 levels have to be kept low in order to facilitate the malolactic fermentation, which makes this a risky time in terms of poten- tial brett growth. Other preventive steps include avoiding lees aging, keeping barrels topped up, keeping cellar temperatures low, avoiding temperature changes and aggressively cleaning new and used barrels. If brett has been at work on a wine, there are two ways that a win- emaker can deal with the problem. The first is to strip out the remaining These microphotographs of brettanomyces, also used on this story's opening page, were taken by Samuel Aeschlimann and provided by Eureka Brewing (eurekabrewing.wordpress.com). { wine science } Somm Journal June/July.indd 104 5/9/14 12:13 PM