Boiling bottle caps

If you're using normal caps, you can boil or sanitize. I wouldn't follow the advice of boiling them with the priming solution though, if only because the caps would get sugary and sticky.

If you're uncertain about whether to boil or sanitize, why not handle them the same way that you handled your bottles. After all, the beer is going to be in greater contact with the bottle than with the caps. What's good for the goose is good for the gander.

However, if you're using oxygen-absorbing caps (like these), then you shouldn't be getting them wet at all. Moisture renders the oxygen-absorbing liner useless. So do not sanitize o2-absorbing caps. Updated, see below.

Update: Northern Brewer Chris has provided some more information on the caps I linked to, so I'm going to update this answer. I found these directions on sanitizing o2-absorption caps from a company that sells them. Their directions boil down to:

• Pro-brewers don't bother to sanitize caps, so you can probably skip it.
• If you're not comfortable skipping it, then do not boil the o2-absorption caps.
• If you get an o2-absorption cap wet but don't use it right away, it's now useless.
• Don't use hydrogen peroxide sanitizers (One-Step, B-Bright) on o2-absorption caps.

I've never sanitized my bottle caps in any way, and have never had any infection problems.

if you're mixing your sanitizer correctly, you shouldn't need the heat. the only way any bad things could "hide" from sanitizer is if your caps weren't clean, and if you're using dirty caps, you've got other, more serious problems.

downsides (i'm just guessing):

• difficulty in handling to get the caps to the bottles. i touch the caps with my fingers, and would expect that getting burns whenever i bottle would make me less likely to bottle.
• thermoplasticity of the glue holding the seal to the metal cap. at what temperature will the seal disconnect itself from the cap?

if you're just microbially paranoid, then i can see using heat, but if you're going to go to that extent, why not use a pressure cooker and actually sterilize the caps?

I've always boiled or at least simmered my bottle caps. In my case, I suspect its a hold-over from home canning, where you have a two-part seal, and the inner lid with the rubber gasket gets boiled (or at least strongly heated. Anyway, my usual process is to rinse the things thoroughly to get any dust or whatever surface crud off, and then lightly simmer for a few minutes. I usually let them cool enough to handle, in which case you needn't be concerned with any extra strain on the bottles.

I wouldn't put it in with the priming sugar, just in case. I doubt you'd get any kind of effect in the form of off-tastes, but why risk it?

I'll freely admit that my process is almost certainly overkill, and there's the very slight possibility of overheating the caps enough so that the inner sear could separate from the metal, causing a seal failure. I've never had it happen, though.

A warm cap would contract when cooling theoretically providing a tighter seal, but also possibly causing damage to the bottle.

If you'r worried about taste sterilise separately.