Spike Your Juice is a kit that allows you to turn any 64-ounce bottle of storebought juice into “a fizzy and refreshing alcoholic beverage” in only 48 hours.
Gizmodo gives it a try using Welch’s grape juice as a base:
“I swear you’re making poison,” my wife warns. I pretend I’m not afraid…Just an hour ago, I decided to pour a bit on the rocks since it fermented at room temperature. I tentatively sipped, expecting something that I could barely swallow. Instead, I was brought back to my childhood. Grape freezepops, grape sodas, grape jelly…but with a kick at the end. After 2 1/2 glasses, it makes for a quick, harsh buzz—akin to the helmet of weight you get around your brow from vodka. There’s no way this is 4% ABV—I’d guess it’s closer to 8 or 10%.
The Spike Your Juice website says you can age the wine for up to two weeks.