Mead Lovers Digest #0223

Published in

· 7 months ago

 

Mead Lover's Digest #223                            Sat 09 October 1993 

 
        Forum for Discussion of Mead Brewing and Consuming 
               John Dilley, Digest Coordinator 

 
Contents: 
  yeast nutrient death (chris campanelli) 

 
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Date: Fri, 8 Oct 93 12:49 CDT 
From: akcs.chrisc@vpnet.chi.il.us (chris campanelli) 
Subject: yeast nutrient death 

  
>>  So I'm wondering, did the yeast nutrient somehow kill the 
>>  yeast? The phrase "osmotic pressure" comes back to me from high 
>>  school biology. . . . 
  
  
*  No, I'll bet the _water_ killed the yeast.  And osmotic shock 
*  was probably the cause.  Most yeast packets I've seen instruct 
*  you to hydrate the yeast in water briefly (like a few minutes), 
*  then add the starter solution (wort/must).  When a single-celled 
*  organism is placed in pure water, the water rushes through the 
*  cell wall & membrane in an effort to equalize the osmotic 
*  pressure - basically, to dilute out the relatively high 
*  concentration of "stuff" on the other side (inside the cell).  
*  It's one of those laws of nature & chemistry.  Now, most cell 
*  membranes contain "pumps" to keep that water out, but they can't 
*  withstand pure water for long.  The yeast nutrient probably 
*  allowed them to die less slowly (by somewhat equalizing the 
*  pressure by being dissolved "stuff" outside the cell), but 
*  couldn't save them.  All of your single-celled friends probably 
*  exploded. 
  
You have your facts down cold about yeast cell physiology however 
I don't think that osmotic pressure was the problem.  If osmotic 
pressure were the culprit then wouldn't everyone's dried yeast be 
dying since everyone rehydrates dried yeast? 
  
I think the culprit may either be the yeast itself (a bad or old 
packet) or the yeast nutrient.  I'm leaning towards the nutrient.  
It was not disclosed as to what kind of nutrient was used but I 
wouldn't be surprised if it turned out to be that yellow granular, 
urea-based stuff.  It's not worth the piss it's made from. 
  
Keep in mind that yeast is fed just prior to drying in order to 
build up glycogen stores.  When the cell is rehydrated, it has 
enough internal "food" stores present for any immediate needs.  
Only when the internal stores are depleted does the yeast cell look 
for external sources.  Bottom line is rehydrate in warm water only.  
Any other substances that are present in the rehydrating solution 
are ignored by the yeast (non-toxic substances that is). 
  
  
chris campanelli 

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