The Gemara brings an opinion that salt cannot be cooked in a Keli Rishon unless it is on the fire. The reason given is that salt is as hard to cook as "Bisra D’tura"-the flesh of an ox. This implies that such meat also cannot be cooked in a Keli Rishon that is off the fire. However, Maran (318:9) rules that nevertheless, it is prohibited to put such meat in Keli Rishon. Even though the meat itself cannot be cooked, the juices inside will become cooked. This is how the Rema, Magen Abraham and Mishna Berura understand the Shulhan Aruch, and this is how Hacham David rules in his Halacha Berura.
SUMMARY
It is prohibited to put raw beef into a Keli Rishon, even if it is off the Blech.
