VA cases highlight importance of good ullage management
Oxygen exposure and poor ullage management are the two main causes associated with recent cases of volatile acidity (VA) issues, confirmed by the Australian Wine and Research Institute’s (AWRI) helpdesk.
AWRI oenologist, Matt Holdstock said VA is a sign of spoilage and is quite easily measured as acetic acid.
“It can arise from a number of different causes, and these include wines sitting on ullage or exposed to oxygen for periods of time allowing spoilage organisms, such as acetic acid bacteria, to produce significant quantities of acetic acid under aerobic (oxygen-rich) environments,” he said.
“Other bacteria including lactic acid bacteria can also produce significant quantities of acetic acid in the presence of sugar, as can yeast, in particular Brettanomyces yeast, when grown under aerobic conditions.”
Though not new issues for the AWRI helpdesk, Holdstock said, spikes in VA problems do happen, particularly in difficult seasons.
“For instance in 2011, which was significantly wet with high disease pressure in South Australia and Victoria, there were a lot of disease problems in the vineyard immediately prior to harvest. These translated to a tougher winemaking year and the presence of higher populations of microorganisms capable of spoilage,” he said.
“That vintage we saw a lot of microbiological issues including elevated VA and other spoilage problems. In some cases in 2011, VA was present before fermentation had even commenced.”
Holdstock said VA is not something that every winemaker battles with every year, but the potential for problems to occur is never too far away, especially when moving wines around and storing them in tanks, barrels or other storage vessels.
“A few of the most recent investigations have been associated with a rise in VA post-fermentation and during storage,” he said.
“Keeping wines off ullage and free of oxygen will go a long way towards preventing acetic acid formation and spoilage during storage.”
He said solving winemaking problems, including VA spoilage, can be as simple as asking the right questions and having all the information at hand, early on.
“Getting the complete picture including the history of the wine from crushing through to storage and all analytical data associated with that wine, allows the AWRI’s oenologists to gain the full picture and pin-point where the problem might have started, and what has ultimately caused the issue,” he said.
If a problem is identified, the first port of call should be the AWRI helpdesk during business hours on 08 8313 6600 or by email: email@example.com or alternatively the AWRI website, which is constantly being reviewed and updated.
The AWRI helpdesk service is provided free-of-charge to Australian grapegrowers and winemakers through funding from AGWA.