Timeline for Is oxidation of yeast starters a concern?
Current License: CC BY-SA 3.0
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| May 2, 2012 at 18:10 | comment | added | Chris Plaisier | Based on this White labs article on the Yeast Life Cycle (whitelabs.com/beer/Yeast_Life_Cycle.pdf) the lag phase is the time taken by the yeast to acclimate to their new environment, and then they turn to exponential growth for the next 1-4 days. All during this time the yeast are undergoing fermentation as their primary metabolic pathway. Think this is semantics, but basically the yeast are using O2 during this "Exponential Growth Phase" which can last from 1-4 days. And during this time most of the sugars are converted to ethanol. | |
| May 1, 2012 at 14:43 | comment | added | mdma | I agree that propagation requires oxygen to build the cell membranes, which happens primarily during the lag phase. During the bulk of the fermentation phase the yeast have already done most of the propagation that's going to occur, so oxygen consumption is reduced. Put another way, although the yeast's primary goal is to propagate, the yeast cannot simply go on budding forever - there's just not enough raw material in the wort to continue building more yeast, and so far less O2 is required compared to when the yeast grows exponentially. | |
| May 1, 2012 at 14:17 | comment | added | Chris Plaisier | While I agree with you that dilution will make the oxidization of the starter essentially nil in the whole beer. Your explanation of fermentation and yeast growth is not correct. The Crabtree effect, which states that yeast in high sugar undergo fermentation as opposed to aerobic respiration, doesn't mean the yeast aren't consuming oxygen. Actually it uses all the oxygen it can find to make sterols so that it can make more yeast (think cell membranes). Looked this up a while ago and it went against everything I learned about mammalian cells, but yeast aren't mammalian. ;-) | |
| Feb 12, 2012 at 14:54 | vote | accept | Chadwick | ||
| Feb 11, 2012 at 3:10 | history | edited | brewchez | CC BY-SA 3.0 |
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| Feb 10, 2012 at 16:50 | history | edited | mdma | CC BY-SA 3.0 |
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| Feb 10, 2012 at 16:38 | history | answered | mdma | CC BY-SA 3.0 |