In a two stage dryer, the moisture content of product leaving the chamber is higher (typically 5% - 10%) than for the final product.
After leaving the chamber, the moisture content is further reduced during a second stage.
Second stage drying may be done in a fluidized bed dryer 1. or a vibrating bed dryer 2.
Two stage dryers allow the use of lower temperatures in the dryer, making the design a good choice for products that are particularly heatsensitive.