Stirring biomass is not easy to do in a vertical reactor. A line of reactors has been developed by Parr Instrument Company to function horizontally.   
   
Horizontal reactors enable researchers to mix bio feed stock and other cellulosic materials such as:   
   
straw   
corn stover   
sugar cane   
grasses   
plants   
wood pulp   
wood chips   
fibers   
   
In the horizontal position, the internal stirrers tumble the material rather than try to stir it with a standard vertical stirrer. These custom reactors are secured vertically for loading and then safely tilted horizontally for stirring. They can also be designed to be operated in both a horizontal and vertical position.