First of all, you don't use sorbate. You use potassium metabisulfite, or meta for short. I don't favor wild ferments. They can be very problematic because you sometimes get a culture with bad and harsh flavors. The wine yeasts that are sold were once wild cultures. They were discovered in the vineyards around the world and chosen to propagate because of favorable tastes and profiles, and alcohol tolerance. You also do not know the alcohol tolerance of a wild culture so it's very difficult to know where to set the brix.
When you meta your must, what you are doing is stunning the wild culture so that it can't dominate the ferment, and the yeast you pitch CAN dominate. But the most important thing you're doing with meta is killing bacteria so that it can't use up the nutrient resources and infect the must.
So the way to do this is to meta your must at a rate of 1/4 tsp of powdered meta per 5 gallons of wine and wait at least 12 hrs. Then if you are using pectic enzyme, add it and wait another 12 hrs for it to do its job. Then set your brix, take PH readings and adjust if needed, then pitch the culture. When the yeast becomes active, pitch your first dose of nutrient. Always step-feed the nutrient. You do this by dividing the entire dose in half. Pitch the first half when yeast is active and the second dose when you get to 50% sugar reduction. Nutrient dose for DAP is 1 tsp per gallon of wine.
