[card_zero]

I don't think they're painting the insides, it sounds like the bottling machine has a hopper full of caps, and they rattle around in production and chip microscopic bits of paint off and those stick to the insides and everywhere, until washed off by the booze.

[Groxx]

Ah, yep, you're correct - I was misinterpreting the pictures in the paper. On rereading, they seem pretty clear about it being paint on the outside that somehow gets on the inner surface.

Though also:

>The results show that glass containers were more contaminated than other packaging for all beverages except wine, because wine bottles were closed with cork stoppers rather than metal caps.

So yeah. Cap differences, probably for fashion more than function, which are probably easily remedied.