Not that I'd want to eat one, but it seems as though the basic "building blocks" are taken from bacteria, not the ***** itself:
Article wrote:
Tokyo Sewage approached the scientist because of an overabundance of sewage mud. They asked him to explore the possible uses of the sewage and Ikeda found that the mud contained a great deal of protein because of all the bacteria.
The researchers then extracted those proteins, combined them with a reaction enhancer and put it in an exploder which created the artificial steak.
They do the same basic thing with some garden fertilizers such as Milorganite from the Milwaukee waste water treatment plant: use human waste as a food source for bacteria, then use the dead bacteria as fertilizer. Obviously there's a big difference between garden fertilizer and steaks but neither is being made straight from ****.
I'll do like Twiz though and stick with slices of dead cow.