Just looked this up out of curiosity. For anyone who doesn't have the book, Rose's ricotta loaf is based on 500 g flour, with 250 g ricotta, 100 g butter, two eggs and 118 g water. So the hydration would depend on how thoroughly drained the ricotta. At 50% solids, the dough would come in at about 60% hydration. A dryer ricotta, of course, would bring that down.
ETA: On review, I realize that calculation is wrong. It's actually 65%, estimating the butter to have 12 g water and the eggs 36 g each (74% of 49 g net). Sorry, don't know what I did wrong the first time. Also, at least according to this site, commercial ricotta runs 70 to 74% water, which would explain why the recipe worked fine for Rose.
