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.
Simply move the fermenter to an area that is room temperature, or 68-70 °F. In most cases, too low a temperature is the cause of a stuck fermentation, and bringing the temp up is enough to get it going again.
The most common causes are: Dead (not vital) or unhealthy (not viable) yeast cells. Too little yeast pitched. Too much yeast pitched, causing excessive krausening and loss of healthy yeast through blow off. Not enough nutrients in the wort to sustain yeast activity.
You can tell if your fermentation is stuck if you notice no activity in your airlock and no layer of Krausen in the wort. A lack of changes in the hydrometer reading three days after the start of fermentation and a high amount of sugar in the brew is another tell-tale sign.
Rehydrate yeast in the presence of a rehydration nutrient (Go-Ferm Protect Evolution) and add 2% dextrose. When the yeast is actively ferment- ing, add an equal volume of the beer from the stuck fermentation. Wait 30-60 minutes, then add another equal volume of beer.
If your fermentation is complete, but you aren't happy with the approximate ABV, you can always add more sugar to bump it up. Just make sure to use a yeast strain that is more tolerant to higher ABV, such as a Champagne yeast.
Yeast energizer contains nutrients that will often restart a stuck beer fermentation. Start with 1/2 tsp. per gallon, adding directly to the fermenting beer. More can be added later if your fermentation needs an extra boost.
If the airlock is not bubbling, it may be due to a poor seal between the lid and the bucket or leaks around the grommet. Fermentation may be taking place but the CO2 is not coming out through the airlock. This can also be caused by adding too much water to the airlock.
If the mould has settled in your fermentation jar, unfortunately, you must throw it away and start over. If there is mould, that means that your vegetables have been in contact with oxygen. This is something we want to avoid!
If there are still bubbles in the airlock after 14 days let it sit for another few days, or at least until there is no bubbling for at least a minute or two. Once there is no activity in the airlock, fermentation is complete.
It's possible to use unfiltered apple cider vinegar to start other homemade vinegars—the mother will help you kickstart the fermentation process, including the production of yeast and beneficial bacteria.
Fermentation rates can be accelerated in several ways. Both the lag phase and the active fermentation phase can be shortened by increasing the yeast pitching rate. The initial fermentation temperature can be increased, as can the temperature of the active fermentation.
The primary reason for fermentation to not start is the health of the yeast, or too little healthy yeast, and this is usually the cause. Perhaps the packet or vial of yeast was old and there was little healthy yeast left to do the job.
Leaving the lid and airlock off will allow the primary fermentation to start sooner and continue more rapidly, but it can also leave the fermentation susceptible to contamination should it not start in a timely fashion.
Put the starter in a cozy spot at 70° to 75°F. You should see some activity within 12 to 18 hours. You will want to pitch the wine starter into the stuck fermentation right after you see the level of foaming in the jar peak. This will usually be around 1-1/2 to 2 days.
Generally speaking, wine can't ferment for too long. The worse that can happen is a “miscommunication” between the sugar and the yeast due to either using the wrong type of yeast or fermenting under the wrong temperature. Even if this happens, you can still salvage most if not all wines.
Burping is essentially just opening your bottles ever so slightly during the second fermentation process to release air or “excess pressure” in the bottle. Many brewers recommend burping bottles every day, or every other day while your bottles are fermenting at room temperature.
Cover the Jar with a dark kitchen towel.
Lactic acid-producing bacteria (LAB) (the bacteria that do the work of fermentation) flourish in the dark, and light kills them. UV Light in the amounts that penetrate the Jar seem to be beneficial to yeasts, and is to be avoided.
A spoiled ferment will smell rancid, like rotting broccoli. A good ferment will have a pleasant sour smell. Note: If there's Kahm Yeast present it may have a strong smell, but once scraped away it should have a pleasant sour smell if it's not spoiled. A spoiled ferment may be slimy in texture.
The yeast need this oxygen to grow and to produce important cell wall constituents. It is important to introduce enough oxygen into wort at the beginning of fermentation. Shaking the fermenter will, at best, add about half the recommended level of 10 parts per million oxygen into solution.
You will still see a stray bubble or two, but it probably shouldn't be bubbling more than once every few minutes. If it is, it's possible that you picked up an infection somewhere in your process. Smell the air coming out of the airlock: Does it smell fresh and beer-like?
Within 24-36 hours, carbon dioxide normally starts bubbling through the airlock, as long as everything is working correctly and if the fermenter is sealed properly. Fermentation can take as little as 3 days if you are using a fast-acting yeast and the temperature is ideal.
If you over-pitch, or dump in too much yeast, your squadron of cells might over-accomplish its mission, thereby fermenting too fast and stripping the beer of much of its desired character. If you're aiming for esters and other complexities that arise during fermentation, you might not get them.
Most brewers use ale yeast, which ferments quickly at moderate temperatures. However, some brewers use lager yeast, which ferments slowly at lower temperatures. Therefore, adding more yeast to the wort will not necessarily speed up fermentation. Too much yeast can lead to off-flavours and a shortened shelf life.
Most small producers simply add diammonium phosphate (DAP) to juice and must to provide extra nitrogen and encourage rapid yeast growth. DAP is usually added to juice or must before fermentation is started.