Photo showing the front of a large horizontal autoclave.When sterilizing your substrate,  longer and hotter is NOT better!

 

A temperature of 121°C or 250°F will do the job. Just be sure the complete mass of substrate reaches that temperature for 30 minutes. 
 
The higher the temperature, the more the substrate will become caramelized. That means less nutrition for your mushrooms to grow.  Less food means less growth and lower yields.  
 
If you are managing hotter and longer than necessary, you are throwing money out the window.  It takes a lot of energy to get your substrate to the right temperature for 30 minutes. It is unnecessary to go beyond that.  
 
Careful management of your sterilization process will increase your profitability.

 

Lou