I know a lot of breweries have a house yeast that they use, and in some cases it's their only yeast. I've also heard that most will only harvest up to six generations, due to weak flocculation and ...
I noticed that ale yeasts, so called top-fermenting yeast, floats to the top. Does this mean that the yeast only works on the wort near the top of the fermenter? Assuming that no oxygen or bacteria ...