If you want to make a homebrew clone of a particular beer or you just enjoy the flavors that a particular commercial brewery’s yeast strain provides there is a way to reuse their yeast. First, you need to do a little research and ensure that particular beer is bottle conditioned. For example, I know that Bell’s Brewery use the same yeast for almost all of their beers and bottle condition. I’ve harvested their yeast from a lower abv beer like their brown ale and built it up to use in a successful Hopslam clone. Here is a good article that explains the process:
The first step is to make a yeast starter—a small batch of beer—to feed the yeast, as they’re likely hungry after running out of fermentable sugars in the bottle. A normal yeast starter of about 1000 mL and an OG of 1.040 will do the trick. Here is a great tutorial on making a yeast starter. If you haven’t made one before, don’t worry, it’s really easy.
Once the starter is made, you will want to remove as much of the yeast from the commercial beer as possible without contaminating it, so make sure the beer is chilled and has been stored standing upright. When you open the beer, give the lip a spritz of sanitizer to make sure it doesn’t have any nasty bacteria living on it.
Then, carefully pour most of the beer into a drinking glass , being careful not to disturb the layer of yeast that will have formed on the bottom. Stop pouring as soon as the yeast cake at the bottom of the bottle starts to reach the lip.
Pay attention now. The next step is very important! Don’t forget:
Now drink your beer.
While drinking the glass of beer, either spray some no-rinse sanitizer on the lip and neck of the bottle (such as Star-San) or use a grill lighter or creme brulee torch to heat sanitize the lip of the bottle.
Give the bottle a good swirl to break the yeast off the bottom of the bottle, then pour the yeasty remains into your starter.
I recommend repeating this for two or three beers (get some help if you don’t want to drink them all yourself). That will insure that you have a sufficient amount of healthy yeast to start eating away at your starter.
Wrap the top of your yeast starter container (we recommend a 2-liter Erlenmeyer flask) in sanitized aluminum foil, or use a stopper with an air-lock, and let it sit. If you have a stir plate, great, if not, just give it a swirl every time you walk past it sitting on your kitchen counter. You can also easily build a simple stir plate with parts you might already have around the house.
It may be a day or two before you start to notice any activity in the starter. Remember, it’s a very small amount of yeast in there. Give the starter 3 to 4 days once the activity starts, and when the liquid begins to clear, you can chill it down in your fridge to see how much yeast has built up and collected at the bottom of the flask. If needed, decant the beer off of the top and repeat the starter process to build up the amount of yeast further.
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