The Torah prohibits consumption of blood. Lev. 7:26-27; Lev. 17:10-14. This is the only dietary law that has a reason specified in Torah: we do not eat blood because the life of the animal is contained in the blood. This applies only to the blood of birds and mammals, not to fish blood. Thus, it is necessary to remove all blood from the flesh of kosher animals.

The first step in this process occurs at the time of slaughter. As discussed above, shechitah allows for rapid draining of most of the blood.

The remaining blood must be removed, either by broiling or soaking and salting. Liver may only be kashered by the broiling method, because it has so much blood in it and such complex blood vessels. This final process must be completed within 72 hours after slaughter, and before the meat is frozen or ground. Most butchers and all frozen food vendors take care of the soaking and salting for you, but you should always check this when you are buying someplace you are unfamiliar with.

An egg that contains a blood spot may not be eaten. This is not very common, but I find them once in a while. It is a good idea to break an egg into a container and check it before you put it into a heated pan, because if you put a blood-stained egg into a heated pan, the pan becomes non-kosher.

The sciatic nerve and its adjoining blood vessels may not be eaten. The process of removing this nerve is time consuming and not cost-effective, so most American slaughterers simply sell the hind quarters to non-kosher butchers.

A certain kind of fat, known as chelev, which surrounds the vital organs and the liver, may not be eaten. Kosher butchers remove this. Modern scientists have found biochemical differences between this type of fat and the permissible fat around the muscles and under the skin.