Droopy wrote:
ewww.

Why not just get a plastic milk crate and an appropriate sized piece of
plywood. Put the grapes in your bag, but it in the crate and then pile
about 100 lbs of bricks on the piece of wood.

I think that idea is from Lum Eisenman's book.

Not sure the bricks would be enough ... unless they were lead. I figure
a decent screw type wine press can generate a couple of tons of force -
about 40 PSI on a pressed area about 10 by 10 inches. Now, perhaps take
that same milk crate and get one of those hydraulic arbor presses from
Harbor Freight and you might have something. In the off-season it can
serve its intended use in my garage. The worm is turning!