What To Expect During Fermentation

Fermentation is the waiting-stage.  For the first few batches, some people are  pulling their hair out, checking the fermentor every five minutes, going crazy! 

Don’t worry!  Your beer will be fine!  Even if something does go wrong during your first batch, it probably won’t affect the beer very much.

We get calls from over-protective first-time brewers, like “My cat sneezed on my airlock, is my beer ruined?”, or “My neighbors played heavy-metal music all night, is my beer ruined?”, or  “I had a bad dream about yeast… is my beer ruined?”

What can we say other than, “Probably not.”  You’ve got to relax, because all you can do is wait and see how the beer comes out. 

Frequently Asked Questions:

Q. How long does fermentation take?
A. Only time will tell.  Don’t believe any recipe that gives some specific time, because slight differences between the way you brew and the way someone else brews will change things.  What can make a difference?

  • Temperature–warmer fermentations tend to proceed faster, but your yeast may produce a better taste at a cooler, slower fermentation.  Experience, notes, and reliable advice are your best guidelines.

  • Dissolved gasses–the more oxygen you can dissolve in your wort just before adding yeast, the better and faster you’ll ferment.

  • Water chemistry–issues such as pH, hardness, mineral content & ion balance can change fermentation characteristics.

  • Yeast metabolism–some yeasts are faster than others, and proper preparation of any yeast makes a difference.

  • Amount of yeast pitched–the more the better.  Despite what you might think, it’s almost impossible to add too much yeast.

  • Original Gravity– the more fermentable sugars in the beer, the more work the yeast has to do.

Q. What temperature if best for my fermentation?
A. That depends on the yeast. Most ale yeasts ferment somewhere between 55 and 72º. Lager yeasts prefer lower temperatures, between 45 and 60º.

Q. How do I know when my fermentation is complete?
A. Your first sign is your airlock. When fermentation is complete, no more carbon dioxide is produced, so you won’t see any more bubbles coming through   your airlock.  This is not foolproof, though.

  • Some fermentors, especially primary fermenting buckets, will leak.  This is normal and won’t hurt the beer.  If you open the fermentor and there’s still foaming and fizzing, it’s not done yet.

  • After some time, usually between 5 days and 2 weeks, fermentation is complete. When fermentation activity stops, no more CO2 is produced.  However, there’s still a lot of CO2 in the beer.  If you shake, squeeze, or bump the fermentor, it will let off some gas for a moment or two.  This doesn’t mean it’s magically started fermenting again – it’s just CO2 being released by the disturbance.

  • With a glass fermentor, it’s really easy to see what’s going on and you will know when fermentation is complete.  With a bucket, you may have to open it and check that there’s no more activity.

Q. Did my fermentation stop prematurely?
A. Probably not, but to be certain, use your hydrometer.

Here are some terms you should to be familiar with:

  • Specific Gravity (S.G.) is measured by floating your hydrometer in a sample of liquid.  The hydrometer must float free.  Read the point where the surface of the sample lines up with the scale printed on the hydrometer.

  • Original Gravity (O.G.) is the Specific Gravity before fermentation.

  • Final or Finishing Gravity (F.G.) is the Specific Gravity after fermentation.

  • Apparent Attenuation is the percentage difference between the two.

The Specific Gravity will almost always be “1.0??”.  You’ll need two readings–the S.G. before fermentation & the S.G. after fermentation. 

The apparent attenuation is the difference between the two readings, disregarding the 1 before the decimal place. Complete fermentation is usually indicated by an apparent attenuation of 70-75%.  For instance, an O.G. of 1.040 and a F.G. of 1.010 shows 75% attenuation.

Q.  Should I use a 5-gallon glass carboy with a blow-off tube?
A.  Probably not.  It can be done, but blow-off isn’t very popular anymore… and for a good reason.  Here’s the whole story:

A blow-off tube is used when you have a fermentor that’s all the way full, with no extra headspace for yeast & foam to rise up and sit on the surface of the beer.  The yeast and foam get blown out of the fermentor through the blow-off tube.

A lot of homebrew shops used to recommend fermenting in 5-gallon carboys with blow-off tubes, mainly because they were getting 5-gallon carboys really cheap, and wanted to sell them instead of the larger 6½-gallon carboys you should be using.

But most home brewers are using ale yeasts, and when you use a blow-off tube, you’re blowing out your best yeast!  This caused nice, fast fermentations to slow down and lag along to a weak ending, which causes overly-heavy beers with high Finishing Gravity and lots of off-flavors.

You should be using a fermentor with enough headspace to allow the yeast to stay in with the beer where it belongs!  A 6½ gallon plastic bucket or glass carboy is ideal for this.  5 gallon carboys should be used only for secondary fermentation, where there is little or no foam.

We use a blow-off tube on our 6½ gallon fermentors when making fruit beers, because they ferment so powerfully that they can reach the top and start to make a mess without it.

Q.  What’s this crud in my fermentor?
A.  Mostly yeast.  During fermentation, a lot of yeasty foam is produced atop your beer.  It will leave a crusty ring in the fermentor, this is normal.  Some beers and some yeasts produce more foam than others.

The foam will drop within a few days and the fermentation will slow considerably. Don’t worry if a small amount of foam reaches your airlock. This won’t damage the beer, but you should remove, clean, and replace the airlock.

Don’t be too worried about contamination while the airlock is off.  At this point, so much CO2 gas is being discharged from the fermentor that there’s little chance of something getting in.

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