Pasteurized substrate mix for mushrooms are always made fresh to order. This listing is for 4 bags each 5lb - total 20lb. 20lb is a perfect amount for two mono-tubs (if mono-tub size 54 - 66 quarts). Our substate mix is pasteurized to preserve needed nutrients for fungi. All products are prepared in front of an industrial grade 99.99% efficient at 0.03 micron hepa filter flow hoods.