Propogation of Yeast

I wanted to propogate some yeast and decided to implement my working knowledge of microbes.

After growing up a 300mL culture of WLP008 east coast ale yeast, I spun down the cells at 4000rpm (yes, in a centrifuge) for 15 minutes and then discarded the spent media. I added 30mL of gylcerol and filled the volume to 300ml with sodium phosphate buffer (for a 10% solution of glycerol) and then I aliquoted 50 mL portions into sterile screw top tubes.

Glycerol is certainly an available carbon source for yeast and I am assuming it will be broken down by the organisms when they finally make it into the wort. Alternative preservatives (that would allow me to freeze the yeast) include EDTA and glycerine. Any suggestions on which if any would be better than glycerol. I just used it because it is standard...

Would calcium chloride buffer be a better alternative to sodium phosphate? I'm not quite sure how it will affect the quality of the beer when I reconstitute it.

Thoughts? Comments? Anyone want some yeast?

I'm taking it you are either a biology student or work in a lab?

That's beyond my expertise, but calcium chloride is used in brewing to lower ph during mash/sparge so it will likely not harm flavors in the fermentation.

But whadda I know?

Been reading "Principles of Brewing Science", a light read; I know, but I have only covered the first 40 pages. Hoping to enlighten my brewing subconcious.

Yeah, I'm working on a PhD in biochemistry... homebrewing seemed like the next logical step, especially since my kitchen looks just as much like a lab as my work does.

OK. For future reference I'll freeze with calcium buffer. There are 2 reasons to keep any sort of cells in a buffer, 1. most cells will pop in pure water (because of tonicity); and 2. buffers are [usually] resistant to changes in pH. Any thoughts on chloride ions affecting beer flavors?

I have a soft spot for stouts and weiss beers.

Hi ya graemhoek

So are you using the same amount of yeast,Glycerol,calcium buffer and no water ?
i do this to harvest my yeast http://www.schwedhelm.net/brew/yeast_harv_freeze.html

can i use the calcium buffer and dump the water in this process?
Thanks Daza

After spinning down or allowing the cells to fall out of suspension overnight and discarding the spent liquid media:
5% glycerol
Fill to the original volume with CaCl2 (50-75mM solution depending on the pH of the tap water in your town - more calcium for a lower pH).

By this recipe, you would add 5mL glycerol and 0.73-1.1 grams of CaCl2 to a pellet of cells and fill the total volume to 100mL.

(50% yeast, 25% water, 25% glycerin) is all you need to freeze Yeast.

The calcium buffer is not needed. If the ph is too high or low the dead yeast will even it out. All the yeast will not die. Chloride ions may affect the beer, but I am not sure, so it is best to leave them out as I know they are not needed.

And freeze in a NON-"frost-free" freezer. You do not want the thaw cycles. If your freezer is frost free keep your frozen yeast samples in a small styrofoam cooler packed with freezer packets so that the thaw cycles will not affect your yeast.

Thanks Doug, I'm sure lab standards are overkill for homebrewing.

I'm not sure what you mean by saying 'the dead yeast will even it out' because as any microorganism metabolizes carbon compounds the pH drops whether there are decomposing bacteria present or not from the production of acetic acid, carbonic acid, carboxylic acid, and some more complex acids both from metabolites and dissolved carbon dioxide.

The bottom line is that they won't be doing much in the way of metabolism while they're frozen and should revive nicely so long as they've been properly prepared and frozen.