Finally back to the internet. I am a grad student, but I wouldn't say I spend every waking minute in a lab, just a lot of them. I'll include some instructions for those with a lab, and those without. If you work in a lab, make friends with someone in a yeast lab, it will make life easier. Ok, gonna get my dork on...
Culturing Yeast: I typically walk over to a yeast lab and ask to borrow some YPD (yeast extract, peptone, D-glucose) agar plates. Use a sterile loop (flamed) or pipette to get some of the last bit of a beer that has been poured into a glass and has sediment at the bottom, streak on the plate, grow for a few days at room temp. or at 30*C and you should have colonies. I have no idea how one could do this at home, there has been talk of slants, but that is old school and I have never used them. I do it to remove any possible contaminants (bacteria, etc) so I start from a single yeast colony for my cultures. One could probably just get some yeast from a bottle and put it in a small liquid starter culture of YPD media or DME+Water but your chances of contamination would be minutely higher.
Growing Yeast: I pick one of these colonies with a sterile toothpick or flamed loop and innoculate a small (5mL) volume of YPD (one could also use DME+Water), and grow until dense (overnight usually, gets cloudy, I have no idea what would happen in DME+Water). I then passage the 5mL into 50mL, repeat, then to 1 L. When it is dense, I put it in a centrifuge and spin it down to a pellet, pour off most of the supernatant and resuspend the yeast pellets in a small (50mL) volume of the spent media. This gets dumped into my wort.
Note, for those with lab access, I am not sure if one could even get these things if you weren't (remember to sterilize in an autoclave or by boiling), here is the recipe for YPD Media (yeast media), this is from memory, so I may edit it tomorrow.
10g Yeast Extract
20g yeast peptone
20g Glucose
in 1L water.
The second link up there has good information on media recipes, remember 1% means 1 gram / 100mL, or 10g / 1 L. It also says that laboratory media is bad for propagating yeast for brewing, I haven't done propagating much (read: once for a batch of beer) but a another scientist I know does it for all his beers and it seems to work fine for him.
For freezedowns, that first link up there is spot on, you want 15% glycerol (glycerine...not sure if they are the same) final volume in the frozen culture, this prevents the water crystals from forming and breaking the yeast cell walls. A non-frost free freezer is key if you are planning on keeping them long. One could also just freeze them in small blocks of ice, that should do the trick. I spin a 5mL culture, and resuspend it in a solution of sterile 15% glycerol in water. At home, one could just add glycerol to ~15% to a yeast culture or a settled yeast culture in DME+Water.
Anyone know a microbrewery in CO that needs a biologist/bad brewer/beer drinker? I should be graduating in about 5 months and need a job!
Nerd Off, good night!
