As far as I read recently, currently the liquid to provide the cells with nutrition is gathered from slaughtering cattle. I couldn't find the link, will keep looking, but if anyone has information to the contrary, I'd be happy. I love the idea of meat-taste without animal cruelty and I think it is the way we have to go if we as a species want to survive.

EDIT: https://gemeinsam-gegen-die-tierindustrie.org/en/clean-meat-the-solution-to-the-problems/

In any case, it is important to bear in mind that the production process regularly relies on fresh muscle tissue and continuously on growth serum.

The growth serum is usually obtained from the heart of a calf embryo, for which the calves and sometimes the mother cow are slaughtered.9b Some companies state that they have replaced the calf serum with an algae nutrient solution.10 It also remains to be seen whether this alternative will prevail.

As the domain name already suggests ("Together against animal industries"), this article seems heavily biased, however. If tissue of a calf embryo is required for the serum, that's not a calf, but an embryo, which is slaughtered. Just like abortion is not murder.

Nevertheless, I hope the mentioned algea nutrition solution will prove a viable alternative.