The different components of FermFed DAP Free work in different ways to feed and protect your yeast.
Advanced - Adjusting Your Nutrient Schedule Based on YAN (Yeast Available Nitrogen)
In addition to the nutrients provided by FermFed or FermFed DAP Free, yeast need a certain level of nitrogen to perform adequately. If deprived of nitrogen, yeast are more likely to produce off flavors, most notably hydrogen sulfide. When added at the rate of 1 gram per gallon, FermFed provides 38ppm of YAN while FermFed DAP Free adds 20ppm when added at the rate of 1.5 gram per gallon.
How much YAN do you need? Acceptable levels range from 175 to 300ppm. YAN levels in grapes vary, with grapes from warmer climates often having less. The best practice is to measure your grapes using a commercial wine lab or the
Vinmetrica YAN Test Kit along with a Vinmetrica Meter. If you know your YAN the following is a good general guide:
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175ppm or above = FermFed DAP Free @ onset + FermFed DAP Free @ 1/3 completion (adds 40ppm YAN)
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150ppm or above = FermFed DAP Free @ onset + FermFed @ 1/3 completion (adds 58ppm YAN)
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125ppm or above = FermFed @ onset + FermFed @ 1/3 completion (adds 72ppm YAN)
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Below 125ppm = FermFed @ onset + FermFed @ 1/3 completion + extra DAP
For a full yeast nutritional plan, use
FermStart when rehydrating your yeast, use FermFed DAP Free at the onset of fermentation, and use
FermFed after 1/3 sugar depletion.