Normal practice I would just add 1 packet of "yeast per must, being a 1-gallon must or up to 5-gallons. Focusing on 1 (one) gallon experiemnts, I would think that 1-packet, properly "hydrated" would be ample to use in two separate 1-gallon experiemts if all conditions were met verses using two packets. 1 for each gallon? Has this been tried by anyone?