Short answer (and it might work if your volatile acidity (VA) level is low enough, say, under 0.55 g/L, depending on your sensory threshold) is to bump up your free SO2 and see if the smell goes away. Sometimes what we perceive as “VA character” can actually come from aldehydes, which get bound up with sulfur dioxide. Often that’s all it takes to make the “VA smell” and taste (which are intimately connected in our sensory world) go away or diminish to a point where the wine is acceptable to you.
However, when you get VA or aldehyde in your wine (which can come from many different sources too numerous to recount in this part of the column you should see it as a very large flag of the red persuasion, if you know what I mean. It generally means that you’ve got someone growing in there that you don’t want and it also possibly means that your wine is not as topped up (completely full in the barrel) as it should be.
Bacterial infection, oxidation and VA all go hand in hand so if you bump up the SO2 and that helps (and even if it doesn’t!) you should make sure that your storage containers are completely topped up. Some of us keep smaller breakdown jugs and stainless kegs for this purpose but if you don’t have any similar wine to top up with, see if one of your winemaking buddies does (I always lend a guy at work some of my spare tank samples) or last but not least, go and buy some similar wine (same varietal, same year, if possible) at the store. However, the best thing is always to make a little more than you think you’ll need, or to use some similar wine from your own stash, to remain as authentic as possible to your wine. Of critical importance is not to blend in any wine that is itself infected with spoilage organisms or has residual sugar or malic acid, because that’s like inviting some unwanted guests for a re-fermentation party.
Additionally, while you’re sending a wine sample out for a VA test, you might want to get the pH, TA, alcohol, residual sugar and free and total SO2 levels tested if you don’t have a good handle on those numbers either. I know it sounds like a lot, but to get an idea of how to best “fix” your wine and especially how to prevent it in the future, these are important parameters to know. First of all, the pH and TA will tell you how much acid you have in the wine. At lower acidity levels (say, pH above 3.70 or TA below 0.45) bacteria will be more likely to live and thrive in your wine, a good way to increase VA, or volatile acidity.
The alcohol level can also tell you some information; bacteria are inhibited by higher alcohol levels so if your Merlot is lower than 11%, that might also be contributing slightly to your problem. The RS and malic acid content are important because if you’ve got a stuck fermentation (where the yeast didn’t consume all the sugar or your lactic acid bacteria didn’t consume all of the malic acid), your VA problem might be from the aforementioned microbes trying to finish the job under adverse conditions. VA (and sometimes other stinky compounds like hydrogen sulfide) can be fermentation byproducts excreted by cranky microbes, which can only be removed with sterile filtration.
Get your free and total SO2 tested because you want to make sure that all the other numbers being in the normal range and your wine topped up, you are storing your wine with enough sulfur dioxide to keep microbial growth and oxidation at bay. Every winemaker has a different answer for “what is high enough but not too high” in the land of SO2 adjustment. Too high and you can start to bleach color from red wines and notice it in the aroma and taste. Too low and it’s just not enough to be effective against bacteria and spoilage yeast. You have to look at the pH of your wine too. The higher the pH, the more SO2 you have to add (go to www.winemakermag.com/guide/sulfite to calculate your sulfite additions). Typical levels of desirable free SO2 for whites that have elevated VA is 30–35 mg/L and 28–30 mg/L for reds. However, if the pH is higher than 3.50, I would suggest you bump it up by a few mg/L and keep an eagle eye on your topping.
