I'm a big believer in making yeast starters for my beers. I use a fair amount of liquid yeast which sometimes goes a couple of months between pitches, so making a step-up starter to verify viability and propagate a good pitch of the yeast is key.
Recently I did something stupid: I killed most of my yeast.
I usually store my yeast in the house refrigerator which, unlike my fermentation fridge, is kept at a constant (and cold) temperature. I typically keep the yeast in the back of the bottom shelf, which is the coldest, and also most out of the way place in the fridge, and it's fine there. However, a couple of months ago I had to move the yeast out while cleaning the fridge for Passover (The yeast itself is kosher, but the beer it's in is not) and so I put it in the fermentation fridge. I figured that since I had a lager lagering in there at the time it was probably fine to keep the yeast in there for a while. (And it probably was).
The stupid thing I did was not moving the yeast back into the house fridge after Passover. And furthermore, fermenting an ale in there after the lager, causing the temps in the fridge to shift from 4C to 20C in short order, and keep around 20C for a couple of weeks, before dropping them back down to 8C at the end of fermentation. So yeah, turns out that violent temperature swings and hot temps kill yeast. Duh...
Actually, that's not quite true: These conditions kill older yeast. Yeast that has been recently used, on the other hand, has a pretty good chance of surviving. Problem is, you don't know what survived and what didn't until you try to use it, which is where yeast starters come in. Over the past month I've been making small starters and painstakingly pitching vials of yeast to see what survived and what didn't. The results are, sadly, pretty grim. I've lost a number of strains I can not replace, including my favorite English strain, which was a real issue since I was going to brew an ESB, and I needed yeast. My dry yeast of choice for an ESB is Dunstar Windsor, which unfortunately my LHBS doesn't carry. Luckily, I discovered an old package in the back of the fermentation fridge.
But now comes the tricky question: Did the yeast survive? It was exposed to the same conditions that killed my other yeast and while it was dry, it was also quite an old package. I decided to take the unusual step and actually do a starter for my dry yeast.
The result was spectacular. Within less than an hour of pitching the yeast into 300ml of 1.040 wort, it had foam and very active fermentation. Clearly the yeast was alive and well (I take this as a sign of the quality of Dunstar products). I let it finish and put it in the fridge until I was ready for it. On brewing day I took it out to let it warm up, and started brewing as usual. After mashing and boiling for 15 minutes I drew about a liter of unhopped wort (I boil for 90 min, so I hadn't gotten to the first hop addition yet) cooled it, and pitched the yeast into it (having first decanted most of the spent liquid). My thinking is that if I'm going to pitch a starter at high krausen, as oppose to letting finish and decanting the spent liquid (my usual technique) then the liquid should resemble my actual beer as much as possible. Clearly they are not identical (the started is not hopped) but they have the same malt profile, which is not bad. I continued brewing as usual, cooled, and pitched the slurry.
Fermentation started within hours. High Krausen within less then 24 hours. By 40 the krausen has fallen. I don't think I've ever seen a beer move so fast. It was so fast, in fact, that my fridge was having a hard time keeping up, and the fermentation temperature ended up at 21C instead of 20C. Not terrible, but a little disconcerting. I was very glad to have left as much head space as I did in the fermentor, as I'm sure I would have had a spill otherwise.
So now it's slowing down and doing its thing. I think I'll give this beer a while at fermentation temps to make sure it re-uptakes some of the extra esters the fermentation must have produced, and possible let it lager a bit for extra clarity and conditioning. Next time I'll be more prepared and set my fermentation fridge a little lower to compensate. I think this will be an interesting beer. And if it turns out OK, I'll bring it with me on August 2nd for everyone to taste. :)