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(TONY GENTILE/TONY GENTILE/REUTERS)
(TONY GENTILE/TONY GENTILE/REUTERS)

Why do some red wines have tiny bubbles? Add to ...

THE QUESTION

I’ve noticed that some younger reds – particularly New World wines (though this is a based on my own very unscientific survey) – tend to have a tiny amount of effervescence. What causes this and does it eventually go away with cellaring? Is it considered a desirable characteristic under any circumstances? Is it desired in Beaujolais nouveau, for instance?

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THE ANSWER

Tiny bubbles in red wine can come from several sources, and they’re not always considered a flaw.

Effervescence in wine is a sign of carbon dioxide, the same chemical responsible for carbonation in pop drinks. In sodas, the carbonation is added artificially, while in wine it’s almost always the product of natural fermentation. Yeast feeds on grape sugar during the fermentation process, producing alcohol and carbon dioxide. In still wines, the carbon dioxide is released out of the vat and into the air prior to bottling. But if a wine is bottled before all the yeast has done its important sugar-gobbling work, the interaction between yeast and sugar will continue in the sealed environment of the bottle. The CO2 consequently remains dissolved as a liquid under pressure, just as in a bottle of Coke or, for that matter, champagne. Removing the cork or screw-cap releases the pressure, enabling the dissolved CO2 to escape as a gas – tiny bubbles.

Trapped CO2 is especially prevalent in still wines that are bottled soon after fermentation, such as Beaujolais nouveau. Wines that are matured for months or years in wood barrels have plenty of time to expel any residual CO2 into the air before they enter the sealed environment of the bottle.

Spritz is also an occasional byproduct of wines bottled at cold temperatures (notably many German rieslings) because CO2 is temperature-sensitive and passes more easily from liquid to gas as the thermometer rises. (Think of warm soda pop, which tastes flatter than a glass poured straight from the fridge.) In this cold-bottling case, the CO2 that was supposed to be released into the air during fermentation may not have entirely escaped before bottling. I wouldn’t necessarily call such wines flawed; it’s just a quirk of traditional winemaking, especially in regions with cool autumn climates, such as Germany. Many “still” wines, red or white, that display subtle effervescence can be all the better for it, with a more lively mouth-feel. But it’s a matter of individual taste.

Long-term cellaring will, indeed, tend to diminish the effervescence, at least in bottles sealed with cork. Cork is slightly porous and will eventually permit dissolved CO2 to escape over months or years. The rate of escape depends on the temperature of your cellar – the warmer the cellar, the faster the rate. However, some wines can display a vague effervescence even five or 10 years after bottling.

There are other potential sources of what we perceive as effervescence, though. Various forms of acidity, for example, can transmit the sensation of subtle spritz to the tongue. It would take many more paragraphs than this, not to mention a chemistry degree (nitrogen sparging, anyone?), to do the subject complete justice.

Have a wine question?

E-mail your wine and spirits questions to Beppi Crosariol. Look for answers to select questions to appear in the Wine & Spirits newsletter and on The Globe and Mail website.

Follow on Twitter: @Beppi_Crosariol

 

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