The laws of the prohibition to eat blood and certain types of fats.
1. The Torah tells us a number of times not to consume blood and certain kinds of fat. The prohibition against blood applies to animals and birds but not to fish. (Human blood is prohibited rabbinically but if one has a bleeding wound, he is allowed to lick it.) The fats are prohibited only in kosher domestic mammals – cow, sheep and goats. Not all fats are forbidden – only certain types of fat that are located in the back of the animal near the internal organs. Certain sinews that are forbidden for consumption are also located in the back. In general, the meat with reliable rabbinical supervision has the forbidden fats and sinews already removed and therefore we are not discussing the details of these laws. Regarding the blood, the majority of meat sold in the stores has blood removed as well, but there are still some people who buy fresh meat and remove the blood on their own, so we will discuss these laws briefly.
2. There exist two ways of removing blood – through salting and through roasting on the fire. We will discuss salting first. The meat is washed well from all sides, any wounds or large blood vessels should be removed before the washing. If there is time, the meat should be left to soak in the water for half an hour. After the water runs down salt is spread all over the meat from all sides. One should use the salt of average size. Now the meat is left on a slanted or perforated surface for an hour. If there is no time it sufficient to leave it for 24 minutes. One has to make sure that the blood can float freely without assembling under the meat. After this the salt is washed off.
3. There are special laws regarding salting certain internal organs and in each case one should consult a knowledgeable person for advice. The liver has so much blood that it can not be removed by salting and therefore the second method is used – roasting on the fire. If the meat was not salted within three days after the slaughter of the animal, the blood dries up and it can only be removed by roasting.
4. In order to remove the blood through roasting, the meat or liver is washed well, cut and salted a little and is hung on top of the fire. It is thus roasted until the blood stops dripping. Note that in general the Torah does not forbid the blood until it comes out from the meat. For this reason it is not forbidden to eat a piece of fresh meat even though it was not salted. However, once the meat is fried or cooked, the blood starts coming out and is absorbed back. That is why the meat that was cooked without salting or roasting becomes forbidden.