Every living creature will be food for you; as I gave the green plants, I have given you everything. However, you must not eat meat with its lifeblood in it. Genesis 9:3-4
Many people believe that the instructions regarding food appeared when Moshe received the Torah at Mount Sinai, but actually, this is not true. Genesis 9 clearly tells us that Noah already knew which animals were clean and unclean.
Why did Noah bring seven pairs of clean animals on the ark? The answer is obvious. After the flood, it was going to take some time for the earth to recover and produce fruit again. The clean animals were necessary to offer the relevant sacrifices before Yehovah, and they would also most likely provide food for Noah and his family until everything was restored.
Notice that it was not until after Noah left the ark that Yehovah told him that he could eat “every living creature” (Genesis 9:3), as well as green plants, which had already been given as food to Adam.
What did Noah understand with those words? When Yehovah told him “every living creature” he was NOT saying: “everything that swims, crawls, runs, and flies you can take to the pot.” Rather he was authorizing him to consume those animals that Yehovah had declared edible.
These are some aspects that although not explicitly found in the text, we can infer: the instruction is really limited to those animals on the list already known by Noah.