Why is the back of a cow not kosher?

The back of a cow is not considered non-kosher. In fact, the entire cow is kosher, with the exception of certain specific parts:

* The fat: Most fat from a kosher animal is not permitted for consumption. This includes suet (the fat around the kidneys) and the fat covering the intestines.

* The sciatic nerve: This nerve, located along the back of the cow, is forbidden according to Jewish dietary laws.

* The blood: Jewish law forbids the consumption of blood.

* The blood vessels connected to the sciatic nerve: These vessels, called the "gid hanasheh," are also forbidden.

Therefore, the back of the cow itself is not considered non-kosher. The specific forbidden areas are the sciatic nerve and the blood vessels associated with it.

It's important to remember that a kosher animal must be slaughtered according to Jewish ritual (shechita) for its meat to be considered kosher.