What to Do If Your Fermentation Stops Fermenting
It happens to all brewers. A chugging fermentation, suddenly stops like it hit a brick wall. Grabbing a sample, you look at the hydrometer wondering if your ferment is done. Sadly, you're stuck with a fermentation that won't finish out. Any number of factors can cause a stuck ferment.
If the gravity is close, you could have reached the alcohol threshold for your yeast strain, mashed too warm, or added too many dextrinous malts. Rouse flocculant yeast strains to resume fermentation. Gently, swirl the vessel to stir the yeast back into solution. Other strains will stop for a week before resuming fermentation. Be patient with those.
If the fermentation has dipped too cold, the yeast may have gone dormant. Bring the fermenter to a warm space, rouse the yeast, and stand back.
Nutrient shortage also causes problems. To correct, boil yeast nutrient or energizer and add to fermenter. Wait a day and watch for signs of fermentation.
Pitching another yeast strain, from a yeast cake or another package, can fix a lot of problems. It's best to take a yeast starter at high krausen for this purpose. Think of it as giving the yeast a running start.
The nuclear option is Beano, the sugar-chomping supplement. Beano contains alpha galactosidase. It attacks complex carbohydrates. It reduces them into fermentation-ready simple sugars. A single crushed Beano tablet added to wort drops the final gravity surprisingly low. Be careful bottling a Beano'd brew! Use hydrometer readings to verify fermentation is complete before bottling.
A Ferment That Never Starts
The only thing scarier than a stuck fermentation is no fermentation. Every new brewer experiences a seemingly dead ferment. “There are no bubbles from the airlock” is the chief diagnostic sign. Before declaring the brew dead, take hydrometer readings and check the lid or stopper. Nine times out of ten the problem turns out to be a loose lid or stopper while the beer chugs away.
No fermentation means you may have pitched a bad pack of yeast or pitched while the beer was hot. Reach for the emergency pack of dry yeast, rehydrate, and pitch. Seal everything up and wait for fermentation to kick off.