If you let a piece of fruit rest over time, it will eventually rot, but luckily, that’s not how it works in Animal Crossing: New Horizons. You don’t have to worry about letting fruit sit and having it become rotten. You get rotten fruit a different way.
Rotten fruit came about in New Leaf, where if players were able to plant and grow a perfect tree, they could obtain a rotten fruit. It only arrived at the end of the tree’s lifetime. You would be able to shake the tree seven times, with three perfect fruit on each shake. On the final shake, the tree would produce two perfect fruits and a rotten one.
You wouldn’t be able to do too much with the rotten piece of fruit. Could sell it if you were hurting for bells, or provide it to any of your residents who were looking for fruit from you. They wouldn’t be too happy about receiving a rotten one, but there were no repercussions for doing so. Leaving the rotten fruit on the ground was also a great way to draw in ants. The best way to acquire rotten fruit is to keep turnips for a week. Leave one from over the extended time it’s given to you, and you can freely use it to capture ants.
Even in past Animal Crossing games were slightly unclear on the process. However, when you can get one, prepare for a rotten fruit at the end of the tree’s lifetime.