We planted grapes to shade our deck (which is currently demolished) and they were getting ripe.
Megan decided it was time to press them since the raccoons and wasps were eating them. We cut them down and filled one side of our kitchen sink with them. It was more than we were expecting and probably 5 times what we'd harvested the year before.
The first batch we just tried throwing them directly in the small press that we had. Even after cranking it down quite a bit there were some grapes in the middle that hadn't popped. Must be that great spherical shape that transfers the pressure so well.
So on our second batch we broke the skins with a potato masher. (I had suggested we use our feet but since we weren't making wine, Megan didn't think it was such a good idea.) That seemed to do the trick and we got a lot more juice out of them without having to work as hard.
We ended up with about a gallon of juice by the end. It's sweet and a bit sugary. Pleasant to drink but a small glass is enough. You're welcome to come by and try some if you're in the neighborhood.