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Re-Fermentation Issues

TroubleShooting

Al Slagle — Newberg, Oregon asks,
Q

Last year I added SO2 and bottled a rosé at 1% residual sugar. It tasted good, But now it has pushed out several corks and has excessive CO2 in the bottle. It refermented, I guess. Could this be malolactic fermentation (MLF) after bottling due to lack of SO2 protection? What flavors should I expect from a rosé that has gone through MLF in the bottle?

A
Let me put on my thinking cap. Indeed I think you are facing a re-fermentation and I’d bet that it is due to your 1% residual sugar, but perhaps secondarily to a re-fermentation of residual malic acid in the wine. Free sulfur dioxide concentration diminishes in the bottle over time and after a year levels would certainly be dangerously low. If you didn’t also sterile filter your wine before bottling, it’s very likely that ambient yeast and malolactic bacteria decided to chew on the tasty “food” left in your wine. The changes they can wreak in the bottle can be significant. I tend to avoid MLF at all costs with rosés, or “pink wines.” Especially for delicate grapes like Pinot Noir where the color is quite unstable, malolactic fermentation tends to create an orange cast to the wine rather than a bright fresh pink. Additionally you might expect some “buttery” type aromas. Malolactic fermentation naturally decreases a wine’s acidity so you will also experience less acid on the palate. It also can cause fizziness from dissolved carbon dioxide (hence your pushed
Response by Alison Crowe.