Mould a kind of fungus, is generally thought of as an undesirable growth, but among the thousands of species of mould there are many useful kinds. Two examples are the white mould which grows on the outside of certain soft cheeses (Penicillium candidum or P. camemberti, or Monilia candida), and the blue mould inside blue cheeses (Penicillium glaucum, or P. roqueforti, or P. gorgonzola). Both soften the texture of the cheese, by producing enzymes which break down the milk proteins. They also develop the flavour by depositing products of their metabolism. In all this, moulds collaborate with other micro-organisms, namely yeasts and bacteria.
