It is not hard to see why investors are excited. Demand for meat and fish is soaring, particularly among the rapidly growing middle classes in parts of the developing world. Making that meat the old-fashioned way uses a lot of land and produces gigatonnes of greenhouse gas. Much of the fish people want is not caught sustainably, and some comes from endangered or threatened species. Plant-based substitutes can meet some of the increased demand, but currently they only really compete with processed products such as those based on mince.