Marie, hydration is based on weight, not volume. So for 75% hydration, you'd use 4 ounces flour (a scant 1 cup) and 3 ounces water (6 tablespoons). It's true, the starter will very gradually become more "hydrated" due to the formation of alcohol, but I wouldn't worry about keeping it at exactly 75%; just keep feeding it with those same proportions. Your starter will be stiffer than normal; most starters are 100% hydration. But if you want 75% hydration, then the info. above is how to achieve that. Good luck - PJH

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