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FW: Question : stuck ferments

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  • Ackland, Tony (CALNZAS)
    Here s an interesting reply I ve had from Mike Ingledew (author of the article Alcohol Production by S.cerevisia : a yeast primer in the Alcohol Textbook)
    Message 1 of 1 , Mar 6, 2001
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      Here's an interesting reply I've had from Mike Ingledew (author of the
      article "Alcohol Production by S.cerevisia : a yeast primer" in the Alcohol
      Textbook) regarding my question ...

      > One question I'd like to ask you if I may ...
      > you've made the point that
      > insufficient nitrogen can deprive the yeast,
      > preventing it from continuing
      > to grow, and thus become "stuck", particularly
      > with high sugar content
      > washes containing little else in the way of
      > nutrients / solids etc (my case -
      > 5kg of white sugar in 20L of water).
      >
      > Why is it too late to provide nutrients or new
      > yeast after the fermentation
      > has become stuck or sluggish ?


      Mikes reply .....


      ... To answer your question, when
      a yeast is deprived of a nutrient, it grows as best as it can with what is
      available, and then growth comes to a halt. Those cells are then put
      together
      with less than satisfactory levels of (lets say) protein due to deficient
      nitrogen. Their enzyme content is less than adequate, and they don't
      metabolize well at all. Growing cells are ~33 x faster at ethanol
      production
      than non-growing cells. Supplementation at that point does not reinitiate
      growth in the older cells. By that time the medium is higher in alcohol and
      still deficient in some nutrients. Some cells may even have died. If you
      have
      tried to ferment sugar in water you will already have experienced failure to
      end ferment.

      when I then asked ....

      > But the combination of supplying BOTH nutrients
      > and new yeast will get
      > activity restarted again ? Or does the new yeast
      > have trouble adapting to
      > the already high alcohol content unless carefully
      > conditioned/stepped up to it ?
      >

      Mikes next reply was ...

      Very difficult (maybe even impossible in many situations) to
      restart regardless of additions. Mike



      So the learning from this is to ensure that we have adequate levels of
      nutrients (mostly nitrogen) available BEFORE we get the wash starting to
      ferment; too late is too late.

      The most commonly referenced sources of nutrition are ammonia and diammonium
      phosphate. Just be careful, that if you're using a fertilizer to supply it,
      that there is no urea present in there too, as it can lead to making trace
      amounts of urethane, a carcinogen

      Tony
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