I have the same issue with corn but with me, it's nitric acid. Roasting corn, when it 'carmalizes' just before it ignites, it gives off nitric acid vapor which condenses in the venting because it's cooler than the stove itself. It combines with the soot from combustion and it will eat the stainless liner in the pellet venting eventually, so I take mine apart every year and wash the inside of the venting with ZEP Purple Power and my pressure washer and clean all the deposited soot and nitric condensed vapor out. If I don't, the nitric will eat the liner out.. You can wash with baking soda and water solution to neutralize the acids.
Why, just before end of heating season, I run straight pellets for a few days at a high burn rate to rid the stove itself of the nitric condensed vapor. Even doing that, the interior of the stove (steel firebox) get's etched a bit. The disadvantage of burning corn.