2. How much can be harvested from each skim, and how many times can one skim from a single batch? In other words, does removing the entire yeast head affect the donor beer's fermentation?
Many brewers skim their crop when the wort hits 50% apparent attenuation. I recently discovered that this practice is not optimal with true Yorkshire strains. The mid-head has to be "beaten" back into the wort, or one will end up with a diacetyl bomb. I am now waiting until the end of fermentation to take my crop when using Yorkshire strains.
I just used for the first time White Labs Burton Ale (WLP023) I wonder if it is a "Yorkshire" type?
I cropped this at 48 hours. I checked on it at 24 hours after pitch as that is the ballpark 50% attenuation time per White labs ( http://www.whitelabs.com/yeast/wlp023-burton-ale-yeast ). But, at 24 hours the yeast on top was very foamy and didn't look dense enough to harvest.
At 48 hours the crop was much better (I didn't discard 1st skim but this is a practice I need to start doing). This morning, 60 hours after pitch, the yeast was blowing off through blow off tube (SS brewbucket). I am now thinking that the stuff blowing off is really what I wanted to harvest.
I hope I like this strain, it appears to be a true top cropper, and easy to spot when "it's ready" to harvest.