Heres some random rememberings from Perth.
Pitching a vial of Whitelabs into 600 ml of wort to step up isnt much help. It wakes the yeast up, gets the metabolism going, but there isnt enough food for multiplication. To properly step up, pitch it to minimum 2 l.
The magic number for dissolved oxygen is 10 ppm. This is easy to get by injecting O2, and can get there by injecting air for longer. The most vigorous shaking might get you to about 6 ppm, which is probably enough for most yeasts. But different yeasts have different O2 requirements. Chris woud consider 12 hrs the latest to be adding O2.
The best by date on a vial is the time when cell count will have been reduced by half, assuming some rough handling on the way. In reality they can be revived after a year without fear of mutation.
CO2 presence/pressure has a big impact on yeast activity. Shaking/stirring starters is just as much about degassing CO2 as adding O2. Ferments should be noticeably better without an airlock adding back pressure. A CO2 pressure of 100 kPA is enough to damage yeast.
You can make nice bread with beer yeast, but you have to leave it at least overnight in the rising stage.
Dried yeasts have to be grown in beet sugar to get a high enough cell density, whereas liquid yeasts are propogated in malt. Dry yeast quality control typically requires less than 1 lactic bacteria per million yeast (I think, or did he say thousand?). Anyway, the liquid yeast limit is zero. So Chris is saying (as you would expect him to) that a liquid yeast is inherently more pure than a dried yeast.
For short term storage of slurry, under beer is just as good as under distilled water, when you take into acount the potential to contaminate during the transfer.
You can successfully freeze yeast. But it needs to be at least -60 degrees for long term storage. Whitelabs use cryogenic long term storage. At normal freezer temps, the yeast isnt completely inactive, and damages itself trying to move around.
