I always clean my SS conical after kegging with barkeepers friend. I rinse it very well. After I let it dry, I came back and saw a water stain dripping down. I wiped it off and saw a gray film on my cloth. I wiped further and I got more gray film. Not good for the next brew. What can I do to get it 100% film free? I use star san in it on brew day, but I would like to have it clean to start my brew day.

Thanks,

3 Dogs

I would see about using some pbw. Try that sounds like the acid in bkf needs to be netrualized. Guess for that matter a little baking soda in a water rinse could work too.

I wouldn't use BKF that often. The benefit of using it is to "re-stainless" the stainless steel. when using BKF, srub hard and rinse well. You should also towel dry the stainless after rinsing. That grey film is the metals that you are dissociating with the BKF. When I use BKF, I let it dry for a couple of days and then wash with regular soap and water and dry again.

clean with PBW between batches.

BKF has Oxalic acid in it.
http://www.barkeepersfriend.com/files/f ... S-2011.pdf
Palmer's book says it helps in passivation of SST
http://www.howtobrew.com/appendices/appendixB-1.html
But he doesn't explain whether the action of oxalic is like Citric and nitric or if it merely does not do what the bad acids and caustics do.
I have read that oxalic does benefit the ORP condition on the surface of SST. So maybe it's an aggressive passivation acid like citric and nitric.
Some acids can be used for passivating SST like Citric and Nitric. Some like the hydrochloric in Muriatic will strip the passive layer away and also strip the surface chrome away too leaving rust-worthy surface behind. Some of the bad acids can be found in food.

To expand on Cliff's comments, in generally mineral acids like sulfuric & hydrochloric to name a few should not be used on SS, although some like nitric & phosphoric are perfectly fine. Also in general organic acids like citric & oxalic are perfectly fine to use on SS.
I'm thinking the gray film is the talcum powder which isn't soluble in water, but is in acidic solution. I would probably wipe as much off as possible, then hit with like starsan or other mild acid cleaner solution (without talcum) and wipe again.