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A friend gave us a bottle of homemade red wine a year ago. (They're Italian and they make wine every year). It's been sitting in our dining room, stored on its side. We started to notice that the cork was starting to push itself out.

We uncorked it, poured a few glasses and tasted it. It still tastes fine, but the wine has a little fizz to it. I drank a small glass 30 minutes ago and I still seem fine. :)

Why is there some fizz to it? Is it still safe to drink?

What are the signs of a bottle of wine that is not safe to drink?

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4 Answers 4

It sounds like it was bottled, intentionally or otherwise, with sugar present in the wine. The residual yeast digested this sugar turning it into alcohol and CO2, providing the fizz. It's safe.

Wine generally doesn't get "unsafe", it goes bad. As wine is exposed to oxygen it turns to vinegar. This is safe but unpleasant to drink.

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Unfortunately, part of hobodaves answer is wrong.

The fermentation does not stop when there is no sugar left in the wine, but when the condition for the yeast that eat the sugar and produce alcohol and CO2 do not permit it to live there any longer / multiply at a sufficient rate. usually, this happens not due to lack of sugar, but to the rise in the alcohol concentration of the wine.

If you start with grape juice that is very sweet, a lot of the sugar will still be left in the wine and you get a sweet wine. If you start with a low amount of sugar you get a dry wine.

The other main control mechanism for the fermentation is acidity.

Additionally, if after the largest part of the fermentation, the yeast is not completely removed from the wine, the fermentation will continue at a very slow speed, making your wine fizzy if bottled in this state.

Sometimes, wine does rot and the cork gets to smell just as horrible as the wine does. Do not worry, the wine is absolutely horrible and is in no way drinkable. It is impossible to mistake it for something "still ok to consume" :)

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Good point-- note, too, that different yeast strains have different alcohol cutoffs, so it's possible to make a sweet, 12% abv bottle of wine, for example. Also, some commercial wines are pasteurized prior to bottling, which kills all yeast and thus prevents any further fermentation. –  kevins Sep 6 '10 at 15:40
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Pasteurized wine is very dirty hack that should disqualify a wine from being labeled a wine, just like adding sugar to the wine. The other main control mechanism for the fermentation is acidity. –  Bogdan Belcea Sep 6 '10 at 15:58
    
I think you're splitting hairs - given the context to the question, the most likely reason is that the wine was bottled with sugar - either intentionally or because it hadn't finished fermenting. The answer isn't wrong, more a simpliifcation. –  mdma Jul 8 '13 at 22:51

Beyond the answers presented above, there is an additional type of fermentation besides the fermentation of sugar to alcohol. This fermentation is called malolactic fermentation and can look like a fermentation of sugar to alcohol. It happens when some of the malic acid is being converted to lactic acid. This is usually good for your wine. It's also usually done before bottling, but as a novice home winemaker I can testify that there's a lot of variables in the process!

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+1 This is definitely a possibility even without sugar. Malolactic fermentation is seen as beneficial for red wines as lactic acid is softer tasting than malic acid, which has a strong bitter/sour flavor. Red wines tend to have more potential for this type of fermentation, too, as the malic acid comes from the grape must, to which they have a longer period of contact. –  kevins Sep 6 '10 at 15:45

Presence of a fizz depends on wine production methods. Intentionally or not there might be fizz in it. I guess your friend has presented you with a bottle of sparkling wine. I'm not a sommelier but after drinking quite a lot of different young/sparkling wines I can tell that the only problem occurred - (very rarely) slight indigestion if the wine was too young.

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