I first read about this on THE COMPLETE CORNCOB PRIMER
http://pipedia.org/index.php?title=The_Complete_Corncob_primer
Breaking In Cobs *
Advice offered by SmokeyTheWerewolf was so good I asked his permission to include it in the Corncob Primer. Thanks very much Smokey.
People say that cobs require no break-in. Compared to a briar pipe, I suppose that's nearly true, but there is a bit of a break-in period.
With the first few bowls in a new cob, when you get near the bottom, that wood from the shank inside the bowl will start to burn. When it starts to taste bad, I stick with it just a few puffs more to help char that wood out of there. Then I sit the pipe down and let it smolder completely out before emptying the bowl or trying to clean it. I figure while it's sitting there a bit more of the wood may burn, and I don't want to stop it from doing so. After 2 bowls, and then again after 4 bowls I hit that shank with a reamer with very little pressure. I'm only trying to whittle away the charred wood and expose more unburned shank so it will burn out more easily next time. After 6 bowls, your cob should be good and broken in.
In that process, most of the the wood shank will have been burned away. The little spaces to the side and under that shank will have filled with ash and just a bit of moisture making a natural pipe mud that will help round out the bottom of your bowl and provide for better smoke draught mechanics and will help protect the bottom of your cob from burnout.