How do farmers know which eggs are not fertilized?

* Commercial egg production: Most eggs you buy at the grocery store are from hens that haven't been around roosters. This means the eggs are unfertilized by design. The goal is to produce eggs for eating, not for hatching.

* Fertilized eggs: Fertilized eggs are only produced when a hen has been with a rooster. These eggs are usually sold for hatching or used for different purposes like making duck eggs or other specialty products.

How to Tell if an Egg is Fertilized:

* Candling: This method involves shining a strong light through the egg to see if there's a dark spot (the developing embryo) inside. This is more common for hatching eggs.

* Incubation: If an egg is incubated at the right temperature and humidity, a fertilized egg will start to develop and hatch.

In summary: Farmers don't typically need to know if eggs are fertilized in the context of commercial egg production. The vast majority of eggs you buy are unfertilized and meant for eating.