Yes, my first gusher. A 'gusher' is, as you probably guessed, the term used when your beer is overcarbonated and spills out when uncapped. To be a true gusher, you can't have shaken, dropped or frozen the beer beforehand, and it doesn't really count if it only lasts a couple of seconds. A real gusher will pour out what seems like an endless amount as time slows down and you think about all the beer you're losing.
What the hell went wrong? Carbonation was calculated perfectly. The beer was refrigerated. My sanitation was as good (read: paranoid) as ever.
I recalled that my refractometer measurement had put this beer's FG at 1.006 - pretty damn low, but I figured it was just a super active yeast. Furthermore, the yeast used in this batch was a repitch from a previous batch.
My thoughts went immediately to a gusher infection - wherein wild yeast invades your beer and starts to ferment the stuff that your normal yeast won't ferment. When this happens, your beer continues to ferment down to the point where it is nothing but alcohol and water, continuously producing CO2 until your bottles eventually explode from the pressure.
I started to freak, and assumed that I had gotten wild yeast in my WLP300 when I washed and bottled it. To test my hypothesis, I opened up a bottle of batch #12, the Pliny the Elder clone I brewed with a repitched WLP001: GUSHER.
At this point I'm running around like a chicken with its head cut off. I open one more bottle of pliny and two more bottles of hefeweizen, all gushers. I of course drank them, which left me in a less than clear state of mind. Did you expect me to commit alcohol abuse? I think not.
The next day, with a clear head, I start doing some experiments to find the problem. If the infection came from yeast repitching, there shouldn't be an infection in batch #15 or #13, but there would be in #14. If the infection was in the fermentor, it would be in #11 (the hefe), #12 (pliny), #14 and #15 (brewed in the same fermentors as #11 and #12). If it was in the bottling bucket, then #13 would be infection free (and thus have a normal FG) until bottled.
It was then that I discovered that my refractometer readings were off. By a lot. Normally, you can get a gravity reading of fermented wort with a refractometer if you plug it into BeerSmith along with the OG. The problem is that when double checked against a hydrometer reading, the refractometer reading was coming up 1 plato short. Consistently.
Thus it was that I thought my hefeweizen had 88% attenuation and my pliny had 93% attenuation. When I added 1 plato to their FGs and plugged in the numbers, the hefe went down to 75% and the pliny went down to 85% - both normal. Batch #13 also matched the hydrometer's reading perfectly if 1 brix was added.
Note: the refractometer reads OGs perfectly, so I'm not throwing it out. In fact, I may keep using it for FGs if it is consistently off by 1, because I can just add 1 - duh.
So, if the 'infection' didn't cause my beers to overattenuate, why did it cause gushers? Well, apparently it didn't. A pliny I put in the fridge the night before poured perfectly (and tasty, if a little grassy). A hefeweizen I poured several days later after refrigerating for a night also came out very nice (and also the palest beer I've ever managed to make!).
It turns out that because CO2 dissolves better in cold liquids, it is possible to get a gusher simply because you didn't refrigerate your beer long enough. This doesn't explain why my first bottle gushed, but it may have been inadequate mixing in the bottling bucket. I guess I'll never know.
I learned several lessons here - double check your FG with a hydrometer, even if you have a refractometer, refrigerate your beer adequately, make sure your priming sugar is 100% mixed in on bottling day, don't open your beer any earlier than two weeks bottled and RELAX. I learned these lessons the hard way so you don't have to!
I must say, I thought this was a pretty interesting read when it comes to this topic. Liked the material. . . . . Jenny
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