40 gallons!!!
It worked fine until I pulled it out of the press this morning and found that the press released the pressure while I was gone last night. I think that it will still be good but the blocks are not pretty.
The good news is that Gouda, unlike most pressed cheeses, doesn't require a long pressing schedule. If your cheese pressed anything above 4 hours you should be ok, as long as you have a bit of acidification going without going too low.
I don't have my notes with me, but I think I achieve a desired PH mark at around 5 hours of pressing.