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Key Factors Why Wine (Can) Ferment In The Bottle

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Every time I open a bottle of refreshing Vinho Verde on a warm summer day I hear the satisfying hiss of gas escaping the bottle. Remembering that made me wonder if wine ferments in the bottle. If it does, how often does it happen?

Wine will ferment in the bottle if there is sugar and live yeast in the wine at the time of bottling. Secondary fermentation in the bottle is how the best sparkling wines are made. Some types of wild yeast can make wine smell spoiled if it ferments in the bottle.

Let’s examine the factors that affect whether wine ferments in the bottle and how to tell the difference between good and bad fermentation in the bottle. 

Does Wine Ferment In The Bottle
Does Wine Ferment In The Bottle

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Does Wine Ferment In The Bottle

Simply put, wine can and does ferment in the bottle. In order for this fermentation to take place the wine would need to have some residual sugar as well as either yeast or bacteria to convert that sugar into alcohol which is the fermentation process. Sweeter wine has more residual sugar and hence more fuel for the fermentation process.

For the fermentation to happen your wine also needs to be warm enough for the yeast to become active. This is the reason why a wine cellar is kept at a lower temperature than room temperature.

Cellaring allows the wine to be kept cool enough to make a secondary fermentation in the wine bottle more difficult.

If you are storing your wine in a room that is warmer, you are increasing the likelihood that secondary fermentation can take place in the bottle.

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One of the key ways in which winemakers kill the yeast that is active in the fermentation process is by adding sulfites. That is because the sulfites kill the yeast and stop the fermentation process.

However, there is wild yeast everywhere around us, so it’s entirely possible that some wild yeast could come into contact with the wine during the bottling process.

If there is unwanted secondary fermentation taking place in your bottles of wine the wine will become slightly frizzy from the carbon dioxide that is released during fermentation.

It will be more cloudy and can even develop a bad smell. The chances of secondary fermentation are also more likely in organic/bio wines.

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How To Spot (Tell) If Your Wine Started To Ferment In The Bottle

A byproduct of the fermentation process is carbon dioxide gas. Therefore, the easiest way to spot if your wine has started to ferment in the bottle is if you see fine bubbles on the inside of the bottle as the carbon dioxide starts to get produced.

Think of a carbonated drink in a clear glass you will see little bubbles of carbon dioxide either clinging to the sides of the glass or slowly rising from the bottom of the glass to the top.

You will see the same thing happening in your wine bottle if your wine has started to develop secondary fermentation in the bottle. 

Very often this secondary fermentation can produce unpleasant flavors and odors in your wine. If you leave the secondary fermentation to carry on for too long you risk your wine becoming undrinkable. 

If you live in a warm climate, as I do, then there is the risk that you may be storing your wine at a temperature that will allow secondary fermentation to start.

The best way to keep this from happening is to store your wine in a wine cooler that you set to the correct cellar temperature for your specific wine so that the secondary fermentation doesn’t start.

TIP: Did you know some people believe that wine grapes contain alcohol? Find out the correct answer in this article. And if you want to know the correct answers to more wine myths, check out this article.

What Causes Wine To Ferment In The Bottle?

What Causes Wine To Ferment In The Bottle?
What Causes Wine To Ferment In The Bottle?

In order for a wine to ferment in the bottle there needs to be residual sugar in the wine as well as yeast or bacteria. The yeast/bacteria feed on the sugar, releasing alcohol and carbon dioxide. If there is abundant sugar then the yeast/bacteria will multiply and the fermentation will accelerate.

Dry wine contains much less residual sugar and therefore there is less chance that the wine will ferment in the bottle. Even if a dry wine does ferment in the bottle, the fermentation will only be slight due to the lack of sugar.

A secondary factor is that different yeasts have optimal temperatures at which they are active and cause fermentation.

I had the opportunity to sit down with Pau Gomez, the owner/winemaker at Bodega Mil300, and this is how he explained the effect of storage temperature on the bottle fermentation of wine.

If the temperatures are cold enough the yeast can become inactive, almost as if the fermentation process has finished, and can lead you to believe that the yeast has died.

If the storage temperature of that wine increases, the yeast re-activates and the fermentation process restarts. This is quite common in organic wines where sulfites are not used to kill any remaining live yeast.

Pau told me that this is the common belief of how the first sparkling wine was made by accident. The wine had been bottled during the icy cold temperatures of mid-winter.

When the temperatures warmed during spring, the still-alive yeast restarted the fermentation process and created the first sparkling wine.

TIP: Most people assume that storing wine in the kitchen fridge is the best way to keep it fresh for extended periods, but is that recommended? Find out the answer in this articleControlling humidity is one of the most critical features when storing wine in a fridge. Find out more about controlling humidity here.

Is It Good When Wine Ferments In The Bottle

If your intention is to enjoy a “still” wine that has no sparkle, then secondary fermentation in the bottle will not be desired.

Similarly, some of the wild yeasts that can be responsible for secondary fermentation can cause the fruity aromas produced during the first round of fermentation to be replaced by spoilage aromas. 

Something else that Pau Gomez pointed out to me was that if a wine had just a little secondary fermentation and had mild spoilage aromas, these could evaporate off if the wine is decanted for 30 minutes.

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On the flip side, some wines become better after fermenting in the bottle. We need to look no further than the superb array of sparkling wines available, some of which continue to ferment and produce bubbles after bottling.

What Wine Types Ferment In The Bottle Intentionally

When it comes to the intentional fermenting of wine in the bottle we all think of the sparkling wines that are produced in the traditional Champagne method as it is the bottle fermentation that is responsible for all of those fine bubbles.

Less well known is the variety of Prosecco called Col Fondo. The Prosecco we all know is produced using the Charmat method as explained by Madeline Puckette in her book.

This is where the secondary fermentation takes place in pressurized tanks, producing bigger bubbles than you get when using the Champagne method. 

The Charmat method, invented in 1895, is quicker and cheaper, so allows large volumes of Prosecco to be produced each year (355 million bottles in 2015).

Before 1895 Prosecco was bottle fermented. Currently, just over 30 wineries in the Prosecco region of Italy still produce a small supply of bottle-fermented Prosecco called Col Fondo. It is easy to recognize modern-day Col Fondo as it is cloudy from all the yeast in suspension.

Finally, we have Vinho Verde from the North of Portugal. This mostly cheaper fizzy wine has secondary fermentation in the bottle because traditionally it was bottled too quickly to keep up with summertime demand.

Some producers still make Vinho Verde using bottle fermentation, though many have taken to artificially carbonate their wine.

Does Wine Ferment On Its Own?

Wine can and does ferment on its own without directly adding yeast. That is because wild yeast is all around us, floating in the air before landing on plants or animals. That wild yeast is enough to begin the fermentation process.

If you pick and press your own grapes into juice without washing the grapes first, the wild yeast that has collected on the skin of the grapes will transfer to the juice and your juice will ferment into wine.

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Wine will ferment in the bottle if there is any live yeast and residual sugar in the wine when it is bottled. Most wine producers treat their wines with sulfites to kill any remaining yeast and stop fermentation. However, organic wines can still be bottled with the presence of some live yeast.

Traditionally, sparkling wines are made by allowing a secondary fermentation of the wine in the bottle to produce carbon dioxide bubbles.

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