What is the difference between pasteurisation and sterilisation?

Pasteurisation heats a substrate to roughly 65 to 80°C for one to two hours to knock back competing moulds while leaving some helpful microbes, which suits bulk straw. Sterilisation uses a pressure cooker at 15 psi, about 121°C, to kill everything, which is needed for nutritious grain and supplemented sawdust. Rich substrates need sterilising; plain straw can be pasteurised.