If your yeast did not start fermenting within 24 hours from pitching then it must have started later to still be going on day 15. Did you pitch cold or at 80 F.
How much yeast was used? Starter?
All my ales vigorus fermentations are complete within 4 days and the yeast start right away. Some liquid yeast starters start to ferment within 8 hours. I aerate with oxygen or shake the crap out of the carboy and I pitch ales at 75 to 80 F. Once I see fermentation starting I lower the temperature to 63 to 65F.
Fermentor 1: Bill's House Ale II, Fermentor 2: German Helles, Fermentor 3: Bill's Schworzbier (Black Bier)
Tap 1: Bill's House Ale II, Tap 2: German Hefewizen, Tap 3: Nut Brown Ale
Future Brews: Stone IPA Clone, Blonde Ale, Budvar Clone, Newcastle Clone
New toy: Blichmann 27 gallon fermentor
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