I made a 2qt starter on Tuesday, and stepped it up to 4qt on Wednesday afternoon right about at high kraeusen. The Temperature has been at a steady 67°. The yeast is first generation washed WLP004 and will be for a 10 gallon batch of a Sweet Stout. It has been in the fridge for at least 6 months. I suspected I was going to have a blow off, but this thing volcanoed for a few hours before the krauesen fell.
Here is the starter, I got home about 5 hours after pitching the 2qt step-up.
I had a huge foil dome over the top of it (removed for photo) since there was no way a foil cap was staying on. Although, I think that the yeast in there would out compete any predators trying to invade.
I was wondering how much yeast is lost during a blow-off, and of what quality the yeast is (ie. more/less flocculent)?.
My starter is on a stirplate, so I'm assuming that since all the yeast is in suspension, the blow off contains all types of cells (more and less flocculent).
Could someone throw out a number in percentages maybe the quantity of viable cells lost, and the quality of those cells?
FWIW, I need to get a 5L flask, however, even with the additional 1L of headspace, I think I would have still had an eruption.