Motorists all across the United States experienced getting stuck last winter. With record snowfall in the Northeast and any snowfall down south, drivers of cars and trucks found themselves in sticky situations. You try to avoid it in the first place, but when it happens—and it happens to all of us eventually—it pays to have the right equipment on hand to get out.
Beer can get stuck, too, and as with a snowbound automobile, the right tools can make all the difference.
A stuck fermentation is one that falls far short of reaching the expected final gravity, and as with many things brewing, the term is relative. A 1.050 pale ale that hits 1.012 instead of 1.010 probably suffers more from poor instrumentation calibration and repeatability issues than it does from stuck yeast. A 1.100 barleywine that stops at 1.045, though, still has a way to go and needs some help.
Here are a few ways to revive a stuck fermentation.
Make sure fermentation really has stalled.
In case you don’t have enough good reasons to always measure the original gravity (OG) of your wort, here’s another. Maybe you overshot your efficiency and what you thought was 1.060 wort really came out to 1.067. The final gravity is going to be a little higher, but you won’t know this unless you have an OG with which to compare it.
Heat things up.
Warming up the carboy is probably the most reliable way to restart a stalled fermentation. Some yeast strains are more temperature sensitive than others and may require some warmth to complete the job. The Saison Dupont strain is famous for stopping at around 1.035 and refusing to budge until it’s warmed as high as 95°F (35°C).
Ferment up a storm.
Imagine that the contents of your fermentor are the waters of the Bay of Bengal and the yeast cells tiny boats carrying casks of IPA. Give those suckers a maelstrom. Some British yeasts are so stubbornly flocculent that it’s worth giving the carboy a good swirl a couple of times a day just to keep them in suspension until they’re done.
Add more yeast.
Additional yeast may be able to revive a sluggish fermentation, although simply tossing in a fresh pack of yeast may not be enough, especially if most of the nutrients have been depleted. You’re likely to have better results with a method called Kräusening. In this approach, you prepare a small yeast starter, and when it reaches high Kräusen, you add it to the main fermentor. Introducing yeast cells at the height of activity may encourage them to chomp down on what the initial population left behind.
Add even more yeast.
Champagne yeast enjoys a high alcohol tolerance and may be able to rescue you if only a few final gravity points are needed.
Bust out the bugs.
In a worst-case scenario, you can always add any combination of Brettanomyces, Lactobacillus, _and _Pediococcus to see what a little funk and sour can do. The final gravity will almost certainly fall, but the character of your beer will be permanently changed. On the other hand, you could also fall into a happy accident and brew the very best beer you’ve ever made—one you’ll probably never be able to replicate if you tried.