I'm about to open a bottle of Eagle Rare 101 Ten year-old that I bought by mistake. (I thought I was ordering ER Single Barrel.)
The cap on this bottle is the plastic, screw-off kind, with a security ring that detaches along a serration the first time the bottle is opened and remains on the bottle. I've noticed before that this type of cap seems to provide inadequate sealing, but this one is the sloppiest I've seen. I can turn it a half-turn before it runs out of travel and starts to apply force to the serration that attaches to the break-away, security ring.
I've posed a similar question before without prompting a full answer. Do these caps adequately protect the contents from oxidation or even contamination by airborne particulate or gaseous agents?
The cap on this bottle was snug. However, there's nothing to prevent a shopper, while handling the bottle, to loosen the cap up to a half turn. I think that such an action is tempting because the absence of a visible seal makes the bottle look as though it has already been opened. In that case, why not at least start to open it, with the idea of taking a little sniff (dare I say "swig"?) before buying it?
I know that Julian uses this type of cap on some of his bottlings, and I've never had a bottle of his whiskey that I thought was contaminated. In fact, at least one person here has commented that eliminating the cork eliminates one possible source of undesirable flavors. Am I being paranoid about this? (Remember, one can be paranoid and still have real enemies, too. )