Yeasts are tremendous bubblers—the carbon dioxide they exude is responsible for inflating breads and pastries, and they also add sparkle to many drinks. Beer, champagne, and hard ciders get their carbonation (and their alcohol) from yeasts, and so do some soft drinks, which ferment for shorter periods and therefore aren't so alcoholic. This sweet, fizzy Concord grape soda is set to bubbling with a purchased culture of champagne yeast, which gives it a pronounced effervescence. To attain ample carbonation, you have to pressurize the soda in sealed vessels, preferably plastic bottles with screw tops that won't explode if too much CO2 builds up.
- 2 3⁄4 cups pure Concord grape juice
- 2 3⁄4 cups filtered water
- 1⁄4 cup sugar (or 1/2 cup agave nectar)
- 1⁄8 tsp. champagne yeast