Spoilage/Settling?

@ACrumbling After only a month? Is it in direct sunlight?

There are some really helpful discussions of oxidation on this site, and the consensus seems to be that exposure to air can significantly change whisky and sometimes for the worse. But this usually takes place over a longer period of time than a month.

Maybe your kitchen is particularly warm (as kitchens tend to be)? If that's the case then the answer is simple: find a dark cool place to store your whisky.

I think that I know that taste that you are describing. My mother had an almost empty bottle of Balvenie Doublewood, and year later (the next Thanksgiving), it that had a sour note that I did not taste in the freshly opened bottle. (I have to admit that I actually kind of liked it, but my expectations were not particularly high at the time.)

Hmm..in the kitchen but only for a month. I look forward to finding out t the solution to this mystery as the thread develops. Victor seems to be a house expert on the effects of oxidation, so maybe he'll chime in...

@Jonathan Hmm... oxidation is definitely something I'm aware of, having read about its effects here and on other sites as well, though usually I've found it only changes things for the better. I definitely want to emphasize that I've only experienced this sudden change when I've gotten down to the last few pours on a bottle. Before that point everything is fine, then all of a sudden, from one pour to the next, this change occurs. Strange...

@Jonathan Sorry, I should've mentioned in the original post that the bottles are not in direct sunlight.

Interesting and disappointing. I've never had bottles develop a sour note over time, but I've definitely had bottles oxidize in an unpleasant way. As more air seeps into the bottles due to the whisky being consumed there is more air to interact with the whisky so it will speed up the affects of oxidation, however in my experience I generally find the whiskies going extremely bitter and oaky. Happened to my Macallan 12 yr old after about a month or so and it was a nasty shock.

You can decant the whisky into some smaller bottles such as pint bottles and shot size sample bottles as the main bottles contents are consumed. That will prevent nearly as much oxidation and changes in the whisky opposed to leaving it in the main bottle.

You can also purchase a wine preserver which is an inert gas spray that coats the whisky and prevents air from contacting the liquid again preventing oxidation.

Also as Jonathan has stated make sure the bottles are out of contact with direct sunlight and if they're near a heat source such as the stove you'd do better to store the whisky away from that. Pantry, bedroom, etc would all be good spots to store the whisky. Personally I store mine on a couple bookshelves with the bottles hiding from the sunlight. Haven't noticed any undue changes/serious changes for over a year now since I've taken some of these measures.

I recently became a convert to Private Preserve. If you're not familiar with it, @ACrumblingWell, it's a spray-can product that adds a layer of inert gas to your whisky (or wine) bottle and prevents oxygen from interacting with the spirit.

I haven't been using it long enough to vouch for it, but some of the more knowledgeable Connosr members use it and give it rave reviews. Available from several online sources, including Amazon, where you'll usually find some vendor selling it for a good price. One can will take care of about 100 bottles.

@WhiskyBee

The post and also the comments may help you out... whiskyadvocateblog.com/2008/09/…

Good thoughts so far! That was a helpful link, Jonathan, thanks for that. I do see a certain consensus around finishing off a bottle that's reached about 1/4 capacity, but since I don't have many whisky-drinking friends and I find the idea of feeling pressured to rush through my delicious bottles of scotch pretty annoying, Private Preserve sounds like the best option.

Since some of my other bottles have probably already gone some distance toward the same fate, I might have to think about polishing them off before they turn, though I will be sorry to see my Caol Ila 12 go... :(
I do have to say, though, that I find it strange to have to expect a bottle of scotch to sour after only a month, even if it is down to 2-3 inches' worth. It seems a bit absurd. I haven't noticed this mentioned as a common problem.

@SquidgyAsh: "bitter and oaky" could also cover the taste I'm getting fairly well, too. It really tastes like some of the flavors imparted by the cask suddenly get terribly pronounced.

@ACrumblingWell This might sound obvious, but have you had a look at the other factors that might be involved?

For instance, do you wash your glasses yourself, or does your wife/girlfriend or whomever do it? Maybe they just happened to not rinse the glass all that well, and coincidentally it happened twice, both when a whisky was almost done.

It could be something even more innocuous. Could the pH in your mouth be different for whatever reason? Maybe you had some orange juice earlier in the evening and forgot about it, or some other highly acidic/basic substance that would affect whisky's taste.

I say this because unless you're keeping your whisky right next to a frequently used oven in direct sunlight, I'd be very surprised to see such a turn so fast -- especially since it doesn't seem to resemble the more commonly found symptoms of oxidation.

Just a thought. Good luck sussing it out, though. Sounds infuriating!

@HeartlessNinny Never hurts to cover the basics! The old "is the appliance actually plugged in?"-tier problems. ;) I'd wondered about that myself, and figured it was possible my palate might have been compromised on one or two occasions. I'll definitely pour another bit of the anCnoc today on an extra-clear palate and see if the problem persists.

@ACrumblingWell Sounds like a plan! I find that when faced with problems like this, the only way to proceed is to eliminate potential causes and try and isolate the culprit. Good luck.

@ACrumblingWell: And, if all else fails, arm yourself with smaller bottles - 200, 100 and 50ml. sample bottles: When you get to a half bot. fill a clean 200ml. bot. and drink the rest; you will have solved the problem of a small amount of Whisky in a large container.

A kitchen is not really a suitable place for a fine Malt Whisky, no Sir!

Cheers and Good Luck!