If you have added some of the "mother" then it can take as little as 4 weeks. If you just set the non pasteurized juice out, it'll take 3-6 months. I got some PH strips so I know when it's "done" w/out any guesswork but you can taste it from a straw from time to time and be able to tell. So long as no mold grows you're fine. The "mother" will be a white layer on the top, and sometimes theres a few bubbles.