Philly Sour produces kettle sour style beers without additional bacterial cultures. It produces lactic acid during the first half of fermentation and ethanol during the second half. This means early fruit additions will contribute more to acid production than ethanol. If you add fruit during the rest period, then this fruit will contribute more towards ethanol production. Adding a whole packet will yield less sour beer (pH 3.8). Adding 1/4 to 1/2 a packet will yield more sour beer (pH 3.5). Optimal fermentation temperature is 75º F for primary and rest.