Oh wow, a single vineyard producing thousands of grapes per day is definitely a bug. They should produce at most 2 grapes per trellis, which I think would be 80 on a max-size vineyard, which is probably still too much but also not a automatically-win-the-game amount.
I’ve tracked down what’s causing it and it’ll be fixed in the next release, which should be out on the 1st. I’ll probably be extending the time it takes to grow plants too. Thanks for playing and for reporting it!