Compost Pile (IMAGE) Penn State Caption Steam rises from heat generated during initial steps of composting ingredients to make mushroom-growing substrate. Penn State research has shown the process kills pathogens. Credit American Mushroom Institute Usage Restrictions non commercial use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.