Some say that dropping one raisin into a bottle or glass of flat Champagne causes the raisin to attract any dissolved carbon dioxide, making the beverage bubble up again.
In 2017, Hoda Kotb and Jenna Bush Hager demonstrated the trick on the Today Show. After they dropped a raisin into a day-old bottle of Champagne, it became visibly more bubbly.
However, experimenters at America's Test Kitchen found the trick fruitless. To test the theory, they used two four-day-old bottles of Champagne that had been left open.
After placing a raisin in one bottle, they did observe a temporary release of bubbles in it but found no discernible differences between the two bottles they used.
The bottle they dropped the raisin into seemed inferior to a fresh bottle in terms of fizziness and aroma. The trick failed to revive the champagne’s original flavor and mouthfeel.
For the experiment, the bottles used were left open for four days, creating an enormous disparity in the amount of time the carbon dioxide had to escape from the bottle.
Fundamentally, the trick makes no difference because the raisin doesn’t create carbon dioxide but merely captures and redistributes what remains in the Champagne.