FW: Question : stuck ferments
- 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 ...Mikes reply .....
> 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 ?
... 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
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
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
tried to ferment sugar in water you will already have experienced failure to
when I then asked ....
> But the combination of supplying BOTH nutrientsMikes next reply was ...
> 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 ?
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