In line 17 the narrator most likely uses the phrase embalmed beef to convey the idea that

The answer is "the beef has been long preserved, like a dead body."

"Embalmed" signifies a preservation process of a dead body, which we often associate with Egyptian mummies. The narrator of "The Jungle" goes on to say that this meat was "old stuff that had been lying for years in the cellars," which further supports this answer choice.