Since this post is from April 2nd, presumably your issue has worked itself out. How did it go? Did you do anything, or just wait?
Don't rely on the airlock as your sole means of deciding if fermentation is working. As was noted above, bucket lids leak...and the CO2 may not be passing through the airlock.
With most things fermentation, RDWHAHB is the best first action. Your more likely to screw something up that is actually working just fine. But, if you are still worried, don't do anything until you are SURE you have a problem by taking some measurements:
- Always take a gravity reading before "doing" anything. If the gravity is dropping, then leave it alone.
- If you have a pH meter, then take a pH reading. Cooled wort will have a pH in the 5.0+ range (depending on your original mash pH). Once the yeast take over, they will drop the pH down by a full point (or more) into the 4.1+ range. If the pH has dropped, the gravity will start to fall very shortly.
No matter what, don't do anything for 48 hours. Sometimes, fermentations can be less active. or a lag period can be longer than usual. If you pH or SG hasn't changed in 48 hours then its time to do something.
At that point, I would repitch a brand new packet or two-rehydrated in declorinated, sterile water first. Something was wrong with the first packet, I'd use 2 brand new packets to keep the lag as short as possible. 72 hours is pushing the safe limit to prevent infection from something else.
This is the primary reason I use properly sized starters grown from liquid, yeast. Near zero lag, and VERY low risk of infection (given proper sanitation practice). But, it is definately a step up the complexity curve.
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21C is plenty warm. I routinely ferment ales at 16C (61-63F). Granted I'm using liquid yeast, and making large starters. But, 21C is dead in the middle of the recommended temperature.
Hohumm is
spot on for anything over 1.050 or so...anything significantly above starter wort concentration (1.036) is "high gravity" to the yeast. The farther above the 1.036 value the more likely you are to have troubles. It is ALWAYS easier on the yeast to hydrate in plain H2O.
No need to make a yeast starter with dry yeast. It can actually be detrimental---they lose all those reserves that HoHumm described. If you are making a high gravity brew that needs more than one packet of yeast, buy 2. This is assuming that you are using fresh, properly stored yeast packets. If not, then get a fresh, properly stored packet.
You can get most of the benefits of a starter, by rehydrating your dry yeast in a low concentration word with just enough sugar to get them "chewing" (around 1.020) at the beginning of a brew day. It will be hydrated, and already going to town on the sugars in the wort by pitching time. That should cut your lag time in half. You won't get much growth, and they won't have time to use up their reserves. But, they will have had time to reanimate, saving you 6-8 hours of lag time in your precious wort.