Chicken cells feed on a cocktail of protein, sugars and vitamins. The process also requires a cell growth stimulating substance, often made from the blood of fetal cows.
The obtaining of this "fetal calf serum" constitutes a major obstacle to the increase in production. It is generally used in medical research – and it is expensive and controversial. It comes from slaughtered pregnant cows – which means that, for the moment, some cell-based meats made by Just, Inc. and other companies are not actually free from slaughter. Just, Inc. is working to create a new alternative based on plants.