Test for YAN?

You will notice that some yeast ingredients base their dosages on YAN. YAN is yeast assimilable nitrogen, or basically how much nitrogen is naturally available for yeast to feed on.

The lower the YAN, the more nutrient and DAP you will need to add. The only problem with YAN is that it is not really something a home winemaker can test for. It's normally done only in a lab.

If you're really serious, you can test your YAN (yeast assimilable nitrogen), before you pitch your yeast(as soon as you receive your grapes). Most of the labs in California that test for it will provide you results by email the same day they receive the sample. So, if you get your grapes, get a juice sample, and do a normal 24 hour sulfite to kill wild yeast, you can get the results back in time to make a more informed decision about nutrient and DAP additions.

I have personally never done this, but if you're really serious about this you can do it.