Tom Jones asked:
If I would have a stuck fermentation, what should I do to get my fermentation started again?
Cameron Begg Replied:
Possible Causes:
1. Deoxygenated wort.
Get out your trusty Midwestern "gas hatchet". Turn on just the oxygen, not the acetylene, stick the nozzle into the beer and bubble away for a few minutes. A slightly more civilised approach might be to buy an aquarium air pump and porous stone. (One of those setups that blows a cloud of tiny bubbles into the water.) Sterilize the bits and pieces that will be in direct contact with your beer and think carefully about the source of the air which will be blown through your beer. Do you need a HEPA filter? If you are very careful it may be possible to gently shake the CO2 out of the beer and then repeatedly blow air into the head space and shake to dissolve some of it.
2. Yeast strain not able to ferment in high ethanol concentrations.
Find out what are the limits of the strain of yeast you used. If you suspect that your yeast has quit when you are trying to make a very strong ale or barley wine, repitch with one of the special strains designed to work at extreme ethanol levels. Winemakers know about this stuff.
3. Missing an essential nutrient.
Again this is more likely in winemaking than brewing, but a quick fix is to boil some yeast in water to break it down, then cool it and add it to the fermenter.
4. Overheated fermentation
It is possible, particularly if fermenting large volumes of beer in a heat insulating container (thick polyethylene for example) or in a warm place, to have the heat of fermentation go into thermal runaway. This means that the heat produced by the yeast slicing up the sugars into CO2, ethanol and so on cannot escape quickly enough and the temperature of the beer increases until the yeast is killed. You could cool it down and repitch the yeast, but it probably won't taste very good. Invest in a thermometer for next time.
5. The fermentation is not actually stuck.
Sometimes a wort will appear to be stuck but in actual fact it never started to ferment properly. Reasons are usually low temperature for that particular strain of yeast and/or insufficient yeast pitched or yeast not actively fermenting when pitched or a combination of the above. That is why it makes such good sense to always make a yeast starter.
Ron Phillips Replied:
In one word, Prevention. It is much easier to prevent a stuck fermentation than to correct one. While people will go on and on about adding yeast nutrient or energizer, rousing the yeast, repitching with a more attenuative (e.g. champagne) yeast, and (dare I even say it?) aerating the already fermenting beer, none of these measures are necessary if the following precautions are taken:
1. Pitch a sufficient quantity of healthy yeast.
The amount needed will vary depending on the initial gravity of the wort (recommended quantities can be found in any brewing book). Using liquid yeast without an additional starter (just using the swelled "smack pack") is an example of severe underpitching. This does not mean that a stuck fermentation will always happen if you do this, just that it is much more likely to occur. Anyone who attempts to ferment a high gravity beer without making a starter is begging for an incomplete fermentation.
2. Aerate the (chilled) wort.
The importance of aerating the wort before the onset of fermentation cannot be overstated. The current issue of Brewing Techniques contains an excellent article on the use of oxygen by yeast. Without getting too technical, dissolved oxygen allows a faster, more vigorous fermentation with higher attenuation. Also, even a little oxygen helps. So shake, rattle, and roll that carboy, splash that wort into your bucket, or use a mechanical aerating system to give your yeast a good start.
These two factors are by no means the "magic bullet" for all fermentation problems (the importance of proper sanitation, wort composition, and fermentation temperature should not be overlooked). However, if the above guidelines are followed, most instances of incomplete fermentation can be avoided.
Here's the next Query
Tom Jones asks:
Is there a sanitizer solution that would kill the unwanted bacteria almost right away instead of waiting 20 minutes and not be an iodine type of solution that stains and possibly be safe for stainless steel?
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