Is there no minimum threshold for rot?
No. And there never has been. All food has always rotted. Except, as I said, for the brief transitional period that just ended.
The only thing you can do is reduce the amount of rot by ensuring that you have enough warehouses/granaries to hold it all, because it rots
faster outside of them.
(And before I fixed it a year or so ago, if you had too much food to fit in the warehouses, it was treating it as if
all your food was outside of them. And that was when you still had a fixed 500-bushel warehouse, with no opportunity to build more.)