How much yeast do you need to add for 20 gallons of fresh grape must?

For 20 gallons of fresh grape must, the amount of yeast you need to add will depend on the yeast strain and the pitching rate recommended by the manufacturer. Generally speaking, for primary fermentation, you'll need around 1-2 packets or around 5-10 grams of active dry wine yeast or around 2.5-5 grams of liquid wine yeast per 5 gallons (19 liters) of must. For 20 gallons (75.7 liters), you'll need approximately 4-8 packets or around 20-40 grams of active dry wine yeast or around 10-20 grams of liquid wine yeast.

It's important to follow the specific pitching rate and instructions provided by the yeast manufacturer, as different yeast strains may have different optimal pitching rates and temperature requirements. Additionally, nutrient additions such as yeast nutrient or diammonium phosphate (DAP) may be required to ensure proper yeast health and fermentation performance, especially for larger volumes of must. If in doubt, consult with experienced winemakers or seek advice from the yeast supplier or a reputable winemaking resource for more specific guidance based on your particular yeast strain and must conditions.