Seriously, that is what I had heard as well. This is apparently an empirical relationship, however, because I have yet to find an adequate explanation for it anywhere (by that, I mean an explanation of the mechanics of the process from which this pattern arises).
I glanced over that and missed it. Opps.
Have you tried emailing White or Wyeast? They may be willing to give some insight. I don't remember seeing much on their web sites about that but that has been a while, and as the above shows, I'm not that sharp today.
Seriously, that is what I had heard as well. This is apparently an empirical relationship, however, because I have yet to find an adequate explanation for it anywhere (by that, I mean an explanation of the mechanics of the process from which this pattern arises).
This, from the very excellent paper by MB Raines on the Maltose Falcons website:
"Although a 100-fold dilution or step-up seems reasonable for yeast propagation, most breweries (or at least what is taught by brewing schools) advocate even smaller dilutions. The Siebel Institute recommends that yeast be stepped up in 8-fold increments, the British Brewing schools recommend 10-fold increments, and the German Brewing schools recommend 4-fold increments."
This, from the very excellent paper by MB Raines on the Maltose Falcons website:
"Although a 100-fold dilution or step-up seems reasonable for yeast propagation, most breweries (or at least what is taught by brewing schools) advocate even smaller dilutions. The Siebel Institute recommends that yeast be stepped up in 8-fold increments, the British Brewing schools recommend 10-fold increments, and the German Brewing schools recommend 4-fold increments."
Have you tried emailing White or Wyeast? They may be willing to give some insight. I don't remember seeing much on their web sites about that but that has been a while, and as the above shows, I'm not that sharp today.
Yep. I emailed Wyeast, White Labs, and even Jamil Zainasheff who is a (self-proclaimed) yeast expert. None really had a good explanation -- all they could quote are the empirical relations like what you mentioned in your next post. No substantive explanation for why, though.
My curiosity eventually died out and I dropped it.
OK, had a good talk with the YGWMBO (Yeast Geneticist Who Must be Obeyed) tonight about this topic. I got some of the same vague responses alluded to above, but I think we got down to the heart of the issue:
The stepped growing methodology is used for both yeast and bacterial growing techniques in labs (I hadn't considered growing bacteria for some reason, but it seems to be universal and it makes sense in isolated strains, so thought I'd mention it). You're trying to grow a single strain genetic colony and avoid infection from wild type, infection, or to have a colony that outcompetes any mutation.
From a practical homebrew/brewery standpoint, the key is to keep a healthy density of active cells (and high enough alcohol content) in order to not only prevent infection via alcohol content but also for the yeast to out-compete any incoming nasties.
In order to do this, you can't just pitch 1 ml of active cells in dilution into 1L of wort. The yeast has a lag phase that is generally the same no matter what the size of the starter is, so that phase can generally be ignored in the process since it depends on the viability of your sample and how "off" it has been turned by your storage technique and length of time. (Lag phase is the time between exposing the cells to the growth media and the point at which exponential colony growth is occurring)
In order to meet an optical density and alcohol content to keep out infection, you need to build in stages. Each stage keeps a solid base yeast density and builds to something that totally wipes out the competition and you start again. This will help you get to the desired number of cells for your pitch target without a huge lag time between the end of the cell colony's lag phase and the point at which it has reached a viable colony density and alcohol content to push out it's competition.
Hope this helps in the discussion.
Oh, and for background info and to make us brewers feel better, even in lab settings where sterile practices are maintained and everything is autoclaved, done in updraft hoods, etc, infections still occurs. Additionally, mutation is something that we should generally not be concerned with. Mutations happen all the time in a colony and the occurrence of a mutation that is both viable and able to compete with the primary strain is something SO rare that you're more likely to win the lottery. For this reason, I think some of the concern about using 4th, 5th, etc generation yeast cultures for brewing is overblown and irrelevant as long as you keep a healthy number of viable cells and you're able to store properly.
Last edited by Randar; 03-12-2010 at 03:27 PM.
Reason: corrected some late night typos
So the numbers are basically what have worked for others and is largely dependent on sanitation techniques?
Roughly, yes. I don't think there is a "right" number and it is simply a matter of keeping the colony healthy and exponentially growing in a contaminant-free media.
I think if you use a stir plate and practice good sanitation there is no fear to be had in continual 8-10x steps.
Thanks Randa, but I don't think this really answers the question. I believe most that pitching an appropriate amount of yeast, relative to the volume of wort you are fermenting, is necessary to avoid infection.
The original question that has yet to be answered is why a stepped regime of yeast growth will produce MORE yeast than one single pitch in the same (total) volume of wort? It is possible to grow yeast from a single pitch in a large volume without detectable contamination, so I doubt that competition for resources with other bugs/yeast has anything to do with it.
If anyone is interested, I just got a bunch of 16 x 125mm (15ml) glass tubes with caps. I ordered WAY more than I really need. Give me a PM if you are interested.
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