What to do when your beer doesn't carbonate

In June, I brewed what was probably my fourth batch of Belgian style Tripel ale (I didn't keep good records until last August so I'm not sure how many attempts there have been).  Each batch I've made has gotten a little better.  This one was no exception.  I brewed it from an ingredient kit, supplemented with different yeast, coriander, and sweet orange peel.  When I took the last sample from the fermenter for testing, it smelled and tasted great - though obviously flat.

As I often do, I bottled this beer following my usual process.  I cleaned and sanitized my bottles.  I did the same with my caps.  I dropped a Fermenter's Favorites carbonation drop in each bottle, filled it, and capped it.  The bottles were placed in my basement inside a cooler, to stabilize the temperatures and provide protection should a bottle burst open.  I left them for two weeks and put one bottle in the refrigerator.  The next day, I pulled out the bottle, popped off the cap, and instead of the usual "hiss" I heard... nothing.  The beer was flat.  This really upset me because up to that moment it was the best Tripel I'd made.

Fortunately, this is a beer that still tastes pretty good even when flat.  If I can't fix the carbonation issue, at least I won't have to toss the batch.  I researched options online and reached out to the folks at BYO Magazine for advice.  Here's what I learned.  (Many thanks to BYO Magazine for sharing the information and ideas with me when I asked for help.)

Causes of Failed Carbonation

Carbonation issues have only a few possible causes:

• Not enough sugar in the bottle for the yeast to use to carbonate the beer
• The yeast has flocculated out and isn't there to consume the sugar, or has died or gone dormant following a high-gravity fermentation
• The temperature is too high or low for the yeast to do its job
• A bad cap seal is preventing carbonation from building up

Solutions for Failed Carbonation

Just as there are only a few causes, there are only a few solutions:

• Start by moving the bottles to a warmer location, somewhere that tends to stay near the upper limit of the yeast's ideal range.  This will give the yeast the best chance of carbonating your beer as-is.
• If two weeks in a warm climate (80 degrees F) doesn't help, try making a small amount of a wort strong enough to generate a krausen.  When the yeast begins to generate the krausen, uncap a bottle, inject some of this active yeast from the wort into the bottle, and re-cap.  Give it two or three weeks.
• If that still doesn't work, try opening the bottles and putting some dry champagne or wine yeast in the bottle, then re-capping.
• If it still doesn't work, try opening the bottle and adding a carbonation drop to it.  The risk here is that the bottles could burst with the extra sugar.
• If there is a brew-on-premise facility near you, they may have a force-carbonation system for bottled beers.  If so, you could ask for time to use it to carbonate and re-cap the beer.  You'll probably have to pay for the service.
• If you have kegging equipment, you could keg the beer and force-carbonate it.

For the options involving adding sugar or fresh wort, I strongly recommend placing the beers inside a cooler or other watertight and sturdy storage box.  This way if you accidentally overcarbonate the beer and cause the bottles to explode, they'll explode inside this watertight box and not all over your walls, floors, and ceilings.  (Glass cleanup will be simplified as well.)

Results and Analysis

Wanting to save one of the tastiest beers I'd made, I began trying each of the suggestions available to me.  Here's how that turned out:

• Warmer location:  This worked for the last few bottles from the bucket, which probably had the most yeast in them.  (It also told me what the problem most likely was - flocculation.)  All of the bottles from earlier in the process did not yield a result.
• Adding Yeast:  I tried adding "a few grains" of dry Montrachet wine yeast to some bottles and more in others (enough to cover the top of the beer inside the bottle).  None of those bottles seemed to carbonate, despite being kept in a range of temperatures that the yeast would have tolerated.  So, either there was nothing for the yeast to work on or the yeast didn't activate.
• Adding an Active Yeast Culture:  I decided not to try this, or adding sugar.

The next time I do a high-gravity batch, I'll try adding an active yeast culture before bottling.  This is what many Belgian brewers do with their high-gravity beers and may be the best option.

Update 09/27/2015:  I thought I had a second batch come out flat, but it turned out to be my mistake and bad brewing journal-keeping.  I thought it had been bottled for two weeks, when it had only been bottled for one.  A bottle opened last night came out properly carbonated. I have a package of CBC-1 Cask and Bottle Conditioning yeast that I may try activating and pitching into a small starter wort to see if dropping a live, active yeast culture into the bottles of the flat tripel makes any difference.

Update 10/08/2017:  I've had another batch fail to carbonate.  I decided to do an experiment in this case to see if I could get that beer to carbonate in the bottle.  See my post on Rescuing an Undercarbonated Beer for more information.