I guess my question is how do the yeast know when 50 percent of the sugar has been consumed or when 30 percent has been. If your starting gravity is 1.090 then 50 percent will be at a gravity of 1.045. If your starting gravity is 1.060 then 50 percent will be 1.030. So what precisely is the mechanism and the chemistry that compels us to add nutrients at the fifty percent point? Thanks
To answer this, you have to know more about the life cycle of the yeast colony during fermentation. I'm no pro, so I dont have this down step-by-step, but from my understanding..
You do all the steps pre-fermentation.. Fruit/flavor, acidity, sugar levels, etc... The yeast are stored, in their package, in a dehydrated sort of coma, and we rehydrate them. At this point, they intake water and swell back to 'normal', but during this rehydration process you're only bringing back to life one age-group of yeast. They're all in the 'same grade in grade school', for lack of a better analogy. This swelling, is the ONLY point at which these yeast, and their successors, have the opportunity to intake particular vitamins and minerals.
I do know, that when this first generation of cells rehydrates, they soak in particular vitamins and minerals (which are escaping me right now) that determine the thickness of their cell walls. This is important when you understand that yeast dont give birth to new yeast, they divide. Everything. 1 yeast cell uses nutrients to double up itself and splits into 2. The cell wall included. There's no more opportunity for these yeast to intake those minerals, when they come up short and start having thin or failing cell walls. This is why Go-Ferm is so important for rehydration - it contains these particular vitamins and minerals, allowing that first generation of yeast to divide further because of the thicker cell walls taking longer to thin out, ending with a larger and healthier yeast colony.
So you rehydrate the yeast, and they've taken in what they could - so they begin to divide rapidly... We know this as the 'lag phase', or the time in between when you've pitched the yeast and when the cap forms. The original generation splits to create a second generation, and then (if i remember right) both generations split to create even more generations. When does the colony know its big enough to handle the sugars? I dont know.. Or do they just keep splitting until they go almost-terminal? I dont know.
But when the lag phase is over, the whole colony pretty much 'switches gears' into consuming sugars and creating alcohol. At this point, the colony you have is the colony you get. They are either healthy enough to finish the job, or we end up with a 'mysterious' stuck fermentation.
And like us, when these yeast start to age, and change their diet due to exhaustion of nitrogen, minerals, vitamins, etc., they can begin to burp/fart/off-gas or become unhealthy.
Eventually, they dont want DAP anymore. They dont want the sugary cereal for breakfast, the Coke/Pepsi for lunch and the fast food for dinner. But they'll still eat a home cooked meal with a glass of wine.
To sum this up, it's not that the yeast know when 50% of the sugar has been consumed, but instead more along the lines of us using those terms to gauge the age of the yeast colony.
Somewhere I found that with fermaid O and other ammino nitrogen you are actually good up to the 2/3 sugar break.. However, I have been unable to find the reference in which I found that. So I might drop back to using the 1/2 sugar break as my last nutrient addition.
It was in that 'talk with the fermaid people' conversation we had.. Somewhere
Anybody know the difference btw Fermaid K and Fermaid O? I bought some Fermaid K to help with a mead that wasn't going off, so I've got that in my stash.
Thanks, Fran
Fermaid-K contains DAP, while Fermaid-O is strictly organic forms of nitrogen. I think they differ slightly on the vitamins and minerals they contain too, but thats kinda hazy.
