Often, the lid on whatever jar in the centre of the pot under the gauge comes out looking as through it’s been through a war zone.
It will happen both to standard single-use metal lids, and to the re-usable Tattler lids.
It cleans off the Tattlers with the wipe of a damp cloth; it can permanently tarnish a metal lid but as they are use and toss anyway, it doesn’t matter.
It does not affect the quality of the seal, or the product inside the jar.
Still, we were curious why it happened. We wrote to the maker of Presto pressure canners and received this answer,
Our Home Economist has seen this before and feels it’s the plating from the gauge. She agrees it’s not harmful, but it’s sure unattractive. She said this will subside over time.” [1]Presto Customer Service to Randal Oulton. 2 September 2016
It hasn’t been our experience that it has subsided, but again, it’s only a minor cosmetic issue.
It can affect the jar in the middle of the canner.
It can look like a lid is ruined, but the next day, after the jar has cooled and sealed, it can be wiped off Tattler lids easily with a damp cloth. Metal lids may be more “permanently” tarnished, but as though are not “permanent” lids anyway, that is of little importance.
References