In comments to a recent post on my plans for doing partial mash brewing, a-non-y-mous and Joe wanted to know how I recover yeast from bottles of beer.
Well, it's quite easy actually.
I first make a typical yeast starter. I usually boil about 1/4 to 1/2 cup of dry malt extract in about a quart of water. After cooling, I add it to a sanitized half-gallon bottle and affix a sanitized airlock.
Here comes the really hard part. I drink a bottle of beer made from the yeast I want to reculture. OK, that's a lie. I usually drink 2 beers. No, that's a lie too. Typically, I drink 4 of them. The truth is, the yeast from one bottle is enough to reculture, but why not give it a head start. Beside, the beer is good.
I pour out 10 ounces of the beer into a glass (and drink) and sanitize the neck and lip of the bottle. I swirl the remains of the beer and simply dump the yeast slurry into my starter. I repeat for any subsequent beers.
That's it. If fermentation starts and bubbles form by the next day, you are in business. Proceed as usual.
Sometimes you can refrigerate the yeast for use at a later date.
The beauty of this procedure is that it saves about $5 per batch. That can be about 15-20% of the cost for a batch.
I have 5 batches planned for the next month. Of those 5, I only needed to buy one yeast strain (Wyeast 1968 London ESB Ale yeast for a bitter I want to make). The most common strain I reculture is good ol' Wyeast 1056. I only reculture for 4-5 generations. After that I start with fresh yeast. Though, I've never noticed a difference between the fresh and recultured yeast.