Strange stuff in my Lyne Arm.

[pangea]

After running a batch of sour mash I disassembled my "rig" and upon inspection found a thin slivery sheen coating the inside of the Lyne Arm. It wiped out easily. Before running this batch, I ran some water to make sure the system was clean but I didn't look in the arm after the water.

What could this stuff be? I filtered the final product through a coffee filter and then through activated charcoal. It looks ok to me.

Any input will be appreciated.