Can I use yeast in a bottle of home brew or commercial brew to make another batch?
You can, although without a microscope and cell isolation equipment, it can be a bit risky, as you never know exactly how pure the yeast in the bottom of the bottle is. A good general test is to taste the beer in the bottle, if it is clean without sourness or yeasty off-flavors, the yeast in the sediment is probably good enough to use, assuming the bottle is not too old (over 3 months) and the yeast is still alive. Obviously, it is safer to do this with domestic craft brews and your own home brew than with imports of uncertain age. Remember that many imported ales with yeast sediments are fermented with a different strain than the one used at bottling, the bottling strain chosen primarily for its good settling characteristics. To start yeast in a bottle of beer with a yeast sediment, pour off the beer, and then pour the sediment into a yeast starter. Wait 1 to 4 days for it to start (see above for yeast starter instructions).
