The rust is the only issue and if you read the manual for example on a old Van Wert they reccomend that it be damp, not sure why.
It's wet because water is used extensively during processing, when it comes out od the breaker it's completely soaked most of the water drains out from the large piles outside the breaker. From there it goes on stockpiles or loaded into trucks, it's always outside and the rice can stay damp on the insuide of stockpile for weeks without rain. In the case of nut and pea it's washed again over screen with water jets to remove any particles that were generated from falling out of the breaker, moving it around etc. This more than makes up for the water content plus you don't want a dry load of coal going in your basement, trust me. Smaller sizes like rice and buck are generally not washed again but may be if they are really dry.
This water may amount to next to nothing for nut or as much as 50 pounds by my guess for Rice over 1 ton of coal.