Author Topic: Yeast Strain Development with Subsequent Generations  (Read 5195 times)

Offline musseldoc

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Re: Yeast Strain Development with Subsequent Generations
« Reply #30 on: December 11, 2011, 05:58:54 AM »
It's the precipitation of calcium phosphate that releases the H+ and lowers the pH.  Calcium phosphate forms and precipitates out much more easily than magnesium phosphate.
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Offline a10t2

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Re: Yeast Strain Development with Subsequent Generations
« Reply #31 on: December 11, 2011, 09:33:45 AM »
We're pushing the limits of my water chemistry knowledge, but the Net Mash Acidity goes up a lot more per gram of MgSO4 than per gram of CaSO4 according to Bru'N water.  So if I'm trying to add SO4, I get less of a pH drop from MgSO4 than CaSO4.

Per unit of SO4, though, the effect on pH should be about the same. CaSO4-2H2O is 56% sulfate by mass, and MgSO4-7H2O is 39%. So you'd need to add about 44% more MgSO4 to get the same amount of SO4. A mole of Mg also contributes more hardness than a mole of Ca (4.1 mol CaCO3 equivalent vs. 2.5), though, so to add the same amount of SO4 the equivalent hardness contribution is nearly the same.

1 g/gal CaSO4 -> 154 ppm CaCO3 hardness, 147 ppm SO4
1.44 g/gal MgSO4 -> 153 ppm CaCO3 hardness, 148 ppm SO4
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Offline tschmidlin

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Re: Yeast Strain Development with Subsequent Generations
« Reply #32 on: December 11, 2011, 02:43:38 PM »
Using Bru'N water, my water has a base Net Mash Acidity (NMA) of 22.4 for a random grist that is in the spreadsheet.

When I add 1.0 g/gal CaSO4 I get 61.4 ppm Ca, 147.5 ppm SO4, and the NMA is 48.2
When I add 1.44 g/gal MgSO4 I get 37.5 ppm Mg, 148.3 ppm SO4, and the NMA is 35.4

So I've added the same amount of SO4, but got half the increase in NMA.

Maybe Martin can explain why that is.  It could be because of what Wild Knight is talking about above, I don't know.
Tom Schmidlin

Offline oly

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Re: Yeast Strain Development with Subsequent Generations
« Reply #33 on: December 13, 2011, 07:49:34 PM »
For what it's worth, the only time I've run a given yeast out as far as you (7 generations) I had to abandon for the same reason. With the 5th generation it became less attenuative, and it decreased further with each subsequent generation.  This was WY1332 NW Ale.  At the time I was not doing much to oxygenate and coincidentally was reading Jamil's yeast book and came to the conclusion that it was due to poor oxygenation leading to the drop in attenuation with generation.  I don't know if that was truly the cause; I've since started using mix-stir but have not used any one strain that many generations. Just thought I'd throw that out there as a possible cause.

Offline oly

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Re: Yeast Strain Development with Subsequent Generations
« Reply #34 on: December 18, 2011, 10:20:34 AM »
Here is a section of Chris White "yeast" book that talks about underoxygenation causing yeast to be underattenuative after several generations. The graph shows a noticeable decline after 5 generations (looks to me to be a reduction of about 4% ADF):

How are you oxygenating? This looks like a good canditate for what you're seeing.