I was doing a wine tasting for a group of people recently and a woman asked me if I had heard that a raisin will restore bubbles in a flat sparkling wine. I had not heard this and immediately said a raisin couldn’t possibly put bubbles back in a sparking line — it would be like putting the genie back in the bottle.
But the question got my curiosity and online research gives some credence to the gimmick. Bubbles come from carbon dioxide. What’s left of carbon dioxide in a flat sparkling wine will attach themselves to a raisin’s many ridges and emit more bubbles.
I tried this experiment on several glasses of sparkling wine. One was left open two days and emitted no bubbles even when two raisins were added. The sparking wine left open a few hours had more response. And, one left open just an hour got the most bubble action — presumably because it had the most carbon dioxide left.
Unfortunately, the additional bubbles won’t last long, so don’t think you can keep adding raisins to keep the bubble machine going. Frankly, my best advice is to never let sparkling wine go flat to begin with.