I've tried heating hide glue to melt it and save soaking time too, and most of the time it retains little lumps of unmeltrd glue. I think they recommend soaking until it swells, which is not necessarily overnight, before the heating, and then it will melt out without having to heat it extra long to be sure all the lumps are gone - staying hot any longer than necessary is to be avoided when you can, as it messes up grab time etc, tho you'd have to really cook it a while to hurt strength. Also, I think you know better the water-glue ratio when it's pre-soaked. I use a lot of hide glue veneering fortepiano cases, and have started to use it for all case glueing since it does not creep under stress, and yellow glue does, in spite of what the mfgrs tell you. Margaret Hood Fortepiano maker Platteville, Wis.
This PTG archive page provided courtesy of Moy Piano Service, LLC