I have read that you can save a little beer in the bottom of a bottle and add some DME to "re-grow" the yeast. I have also read that some commercial brewers add a different yeast at bottling time to hide the true type of yeast they use to ferment with. How often do breweries really do this? I was wanting to clone a Sierra Nevada Pale Ale. Would I be safe getting yeast from one of those bottles?