We need to keep talking about Brett. Not because it has become a major problem again, but because researchers want to ensure that it doesn’t.
Recent and ongoing work at the Australian Wine Research Institute (AWRI) has found signs that some strains of the dreaded yeast Brettanomyces may be able to develop resistance to sulfites, which are the common – and generally very effective – way of dealing with them.
The problem may be exacerbated by a trend towards lower sulfite levels in wines coupled with hotter vintages, causing pH levels to creep up in some wines. A combination of high pH and lower sulfite can leave winemakers in a grey area; there’s almost enough there to control Brett, but not quite and this can give the yeast the time it needs to evolve and adapt to the challenge.
Dr Anthony Borneman and colleagues have seen tell-tale signs in some recent samples of Brett-affected wine, and now they want more samples to investigate – which is often easier said than done.
‘It can be difficult to get samples because it’s something wineries just want to get rid of’, he said. ‘Winemakers don’t want Brett associated with their wine. So when problems do turn up, testing is done under strict anonymity – we don’t get to study the strains that may be causing current problems.
‘We would be delighted if more wineries would get in touch and offer to provide samples. It would really boost our ability to gauge what is happening right now the field and we’ll maintain their anonymity.’
Dr Borneman and Dr Cristian Varela are leading the current research that builds on a thorough sector survey of Brett that was started by Dr Chris Curtin and Peter Godden back in the early 2000s.
A key recommendation from that original exhaustive work was for winemakers to focus on the now widely used and accepted regime that combines effective sulfite use with appropriate pH management and oak barrel hygiene. Even then, however, the potential for sulfite resistance to develop was recognised, and that has been one of the drivers of the current research.
‘Resistance is a problem that can rear its ugly head in lots of situations – whether it’s the evolution of bacterial antibiotic resistance in hospitals or agrochemical resistance in vineyards in pathogens like downy or powdery mildew’, Dr Borneman said.
‘We decided to have a look at what’s biologically possible – whether spoilage microbes like Brett have the ability to become resistant to the methods we use to control them. It’s a case of the better the devil you know.’
As a result of this work, they now know a lot more about how sulfite interacts with Brett biology at the population, strain and molecular levels.
The AWRI made world headlines in 2011 when it announced the successful sequencing of the first Brett genome. A key part of the recent project was sequencing the genomes of an additional 40 strains of Brett, both to study their genetic similarities and differences and to try to work out what part of the genome might facilitate sulfite tolerance.
Significantly – and contrary to work done elsewhere – work performed by project partner Dr Paul Grbin from the University of Adelaide found no evidence that sulfite causes Brett cells to enter a viable but non-culturable (VBNC) state and that only a very small number of viable and culturable cells is needed for population growth to resume.
Another area of work confirmed the potential for evolution of sulfite tolerance then compared new sector isolates with strains isolated during previous studies. While the researchers stress that their results are preliminary, they show that sulfite tolerance of Brett in Australian wineries may be increasing.
‘I wouldn’t want anyone to lose any sleep worrying about sulfite-resistant Brett ruining the sector tomorrow, but we are at the stage where we would like everyone to be a little more vigilant’, Dr Borneman said.
‘The monster of the early 2000s, where people were losing lots of wine to spoilage, is a distant memory for a lot of people and it’s easy to get a bit too relaxed about controlling it.’