I’ve just done about two hours of research on YAN variations and nutrient needs among fruits and the answer is definitely “it depends”. YAN varies widely by cultivar, year, climate, harvest date, and viticultural practices (like adding nitrogen to the soil or not), and nutrient addition to a must of any kind depends on both YAN and individual yeast needs.
Cornell extension has some good information, as does
University of Vermont. The
Australian Wine Institute has some particular levels for grapes and a DAP calculator.
Penn State has some great information in addition to a good explanation of why it’s bad to add DAP at the beginning of fermentation. Of course,
WineMaker has a great explanation as well.
So... part science, part experience, part style. I haven’t found anything yet that gives a general range of where fruits land on the YAN scale, except for
this article by the NYS AG Experimental Station in Geneva. It seems like GoFerm is helpful at the beginning and end of fermentation as are Fermaid products 1/3 and 2/3 through fermentations.
I don’t have access to YAN instruments, hence my original question in trying to determine what to add when, but it does sound like “it depends”. Too little nutrient will stress the yeast and cause delays or a stuck fermentation and H2S. Too much can cause a huge proliferation of yeast and then a stress when they run out of food and also excess food for other organisms if not enough sulfite is used at the end of fermentation.
There’s a lot of discussion about adding it all up front versus over the course of the fermentation. I believe these may be style or pragmatic points, at the moment. I’m still interested in what everyone does and how “other than grape” fruit wines fare in this arena.