Rusty Bottle Caps

[MarkA]

Does anyone else get rust underneath their bottle caps?

I've had this problem a few times. It's not every bottle in the batch, just two or three occasional ones. The rust is on the outer part of the cap (the bit that folds down the outside of the bottle rim) so it's not affecting the beer, but it doesn't look very good when giving beer to friends etc.

I've tried drying the bottle and caps off fully before capping them, and have still had the odd rusty one. The bottles are stored in a dry place so it's not from condensation or environment.

Cheers