HI
Is it possible to harvest the yeast from a bottle of store bought beer? Say from a Sierra Nevada Hefenwivzen or Duval.
If so, how is i done?
Absolutely, it is possible. For many years, that was the only way I could get good yeast, and I did it every time.
Obviously, you have to start with a bottle of naturally conditioned beer that has live yeast in the bottom. The problem is that some of these beers use a different variety of yeast for carbonation than they do for brewing, so you may not get the results that you want. However, if you get good results with a particular brand, then those results should be consistent.
It isn't particularly difficult to do, but it does take some patience.
Start by drinking the beer, being careful to leave as much of the yeast behind as possible. Then make a small starter (I used to make a 6 fl oz starter using about 1/2 oz DME to 6 fl oz water, and fermented in a 12 oz bottle loosely covered to prevent bacteria dropping in). Giving the bottle a swirl every time you pass by speeds the process up. After 4 - 5 days, your small starter should have multiplied considerably, and can be stepped up.
To step up, I prepared about 1 qt fresh wort using 3.5 oz DME to 1 qt water in a half gallon jug, and transfer the original starter into the fresh wort, cover loosely, and wait another 4 - 5 days (again giving it a swirl as often as possible). If you have a stir plate, you can cut down the 4 - 5 day periods down to 1 - 2 days, and you will end up with more yeast.
-a.
