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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Do you know how to make a yeast starter? Then why not farm yeast and freeze it?

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Old 12-28-2011, 05:28 AM   #81
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Milptak, It takes only a small difference in doubling rates of cells for the faster growing yeast to overtake the population when growing from a low concentration to a high density starter. Unless you start with a very high density population that has not gone through too many doublings, or you are not very particular about what you end up with, I would discourage you from trying to propagate blends of yeast.

It wiil be quite difficult to identify the various yeast in a blend unless you know what you are looking for.

By the way, I intend to thaw out the yeast I froze away in October tomorrow and determine viability and recovery rates. It will probably be pretty crude (hey, I'm on holiday ;-) but will tell us whether there are substantial differences in either parameter.

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Old 12-28-2011, 06:44 AM   #82
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Great thread i was looking for this kind of Info.
Thanks.

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Old 12-28-2011, 03:55 PM   #83
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I work in a yeast lab and as for percentages of glycerol used to freeze down yeast, standard in our lab is to use 15% glycerol and then pop it into our -80C freezer. There is no need to freeze large cultures, 1 ml will leave you with enough cells to go back to your stock multiple times, take a little scrape with a sterilized toothpick or something and grow it up.

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Old 12-28-2011, 04:52 PM   #84
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Quote:
Originally Posted by Mcsuck View Post
I work in a yeast lab and as for percentages of glycerol used to freeze down yeast, standard in our lab is to use 15% glycerol and then pop it into our -80C freezer. There is no need to freeze large cultures, 1 ml will leave you with enough cells to go back to your stock multiple times, take a little scrape with a sterilized toothpick or something and grow it up.
That's what a lot of people do, but that is more of a yeast banking approach. What I'm trying to perfect is a more or less "pitchable" frozen yeast reserve similar to that of a store bought vial or smack pack which is something that not very many people seem to have expiremented with. Since most of the strains I use are readily available for purchase, I don't want to invest much time and money in culturing. Once I have some data avialable on viability after the freeze, I should be able to freeze enough cells so that the end result after thawing is roughly equal to a smack pack or vial. This will also reduce lead time when brewing as I won't have to do small step ups to bring the population back up to sufficient numbers.
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Old 12-28-2011, 05:07 PM   #85
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Ahhh, I see. Personally, I wouldn't recommend that because the long time it would take a large culture to freeze. Also, when you thaw out your yeast reserve completely, you can expect about a 50% loss in viability (i.e. about half the cells won't recover). In our lab, we work a lot with frozen stocks, and this is essentially what we see. This is why it it much more preferential to have a "yeast bank" and make starters from that. So you would need to at the very least have 2x as many cells as a smack pack just to have the same amount of viable cells, not to mention it would be better to have more since your frozen cells are going from dormant to active, so you could expect an extensive lag time before fermentation starts. Another reason why the "yeast banking" is advantageous.

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Old 12-29-2011, 02:41 AM   #86
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Mcsuck, I have already tested a few things in the lab (I'm also a yeast researcher). I have found, as reported in the literature for yeast and as done routinely with mammalian cells, it is best to freeze slowly and thaw rapidly. We have not routinely done this for our yeast library but about 1 degree C decrease per minute and thawing at 37C is optimal. Recently, I have frozen approximately 2x10e11 packed cells in an equal volume of 15% glycerol and frozen by moving from 4C to -30 to -80C over the course of several hours. Those cells thawed a 37 produced a robust starter culture when inoculated into 3 liters of wort overnight. That would be my preferred approach due to the lag time.

However, I am now testing conditions that are approachable by the home brewer and testing viability and growth rates. Doing a pretty crude set of tests. I should be able to report after the 1st of the month on the effectiveness of freezing for several months at -30C after slow and rapid freezing in 15% or 30% glycerol. I won't have good growth curves, just qualitative assessments and I will have crude viability determinations. Counted and plated those cells today.

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Old 12-29-2011, 02:52 AM   #87
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I should add that I didn't do a careful determination of lag time or viability of my starters made from -80 since I wasn't pitching directly. However, I'm guessing that they were getting under way pretty well after 4 hours and were at full density within 14 hours. After that I just cold crashed overnight, dumped the spent wort and then pitched. Fermentation was active within 4 hours. My cultures that were innoculated today were all increasing significantly in density after 3 hours suggesting that the lag is not a problem.

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Old 12-29-2011, 03:13 PM   #88
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I should add that I didn't do a careful determination of lag time or viability of my starters made from -80 since I wasn't pitching directly.
I don't think anybody (including myself) plans to pitch directly from thaw to fermenter (although I have done this for expermentations sake and it did work albeit with less than optimal results). Most people make starters from fresh packs/vials and I plan to always make a starter with the thawed yeast. However, % viability after the thaw is the primary concern so that cell counts can be reasonably estimated before making the right size starter for the target OG. Looking forward to the plate results for the -30 freeze.
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Old 12-29-2011, 04:36 PM   #89
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Viability of commercial wine yeasts during freezer storage in glycerol-based media
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Old 12-29-2011, 05:12 PM   #90
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There is not really any detail in the paper in how the thaw was performed, but 4-7 orders of magnitude loss in viability is a pretty low number. However they are also using different strains and storage conditions.
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