Penicillin surface fermentation vesel, c 1942.

Penicillin production by the mould Penicillium needs oxygen, unlike beer production from yeast. Therefore, the fungus is grown on the surface of a shallow nutrient soup. The sterilisable containers are plugged with cotton wool to stop the air bringing in common bacteria which destroy penicillin. These specially designed flat, stackable porcelain vesels, made by Imperial Chemical Industries' Pharmaceutical Division, proved ideal in the early production of penicillin.