Edible food sensors could let you know:
When a fruit ripens or rots, chemical changes churn around inside it. Those changes and differences in the stiffness of the fruit translate to what’s called their dielectric properties. [Creator Hu Tao]’s gold sensors pick up on that change, and emit a different electromagnetic signal when monitored with a reader. … The working principles behind the sensors are based on existing RFID tech–the difference here is that the sensors aren’t hard electronics, they’re flexible, edible stickers.
On a related note, Jonathan Bloom complains about how much food we waste:
Globally, at least one-third of all food isn’t consumed. Domestically, that figure jumps to about 40 percent. And zooming in further, we squander about 25 percent of the food we bring into our homes.
The Dish 