I transferred three spirits – Auchentoshan Scotch, Crown Royal Canadian whisky and Courvoisier Cognac – to three decanters that I had collected over the years. After a few months (I drank them only occasionally), they smelled and tasted worse. What a waste. Are decanters meant only for decorative purposes?
I'm puzzled by your experience. Decanters have long been used for distilled spirits (ever watch an old episode of Dallas!?).
Storing whisky or Cognac in a decorative glass vessel should have no more adverse an impact than keeping the spirit in the original bottle - providing the stopper provides a good seal against oxygen. Many people do eschew decanters, but generally not for the reason you cite. Most simply prefer to see the bottle and keep track of what they're drinking, and decanters could be considered an unnecessary expense. The other reason is lead. Fine crystal is traditionally made with a proportion of lead oxide (though you can now find many examples of lead-free crystal). There's a widely held belief that this is a potential health risk, especially in cases where the liquid remains in contact with the vessel for extended periods. Municipalities and homeowners have long been replacing old lead water pipes out of the same concern. But I'm not aware that leaded crystal can drastically spoil a spirit's flavour over the course of a few months. Others might disagree.
I have occasionally used non-lead decanters for spirits (though I'm more of the original-bottle type of guy) and have not encountered off flavours. Unlike wine, which is rich with fruit and strongly susceptible to oxygen "bruising" once exposed to air, high-strength spirits do not suffer the same rapid decline. That said, many whisky experts believe a bottle should be consumed within six months to a year after it's opened – less time if the bottle is less than half empty. The same would apply to spirits that have been transferred to a decanter. Yes, oxygen can have an impact, but a much less dramatic one, possibly causing the spirit to taste duller. And if the decanter has a poor seal, alcohol may evaporate, which also can change the character slightly. It also helps to keep the spirit away from direct sunlight, so I hope you were not trying to make your decanters sparkle by placing them next to a south-facing window.
I don't mean this in an offensive way, but did you clean and thoroughly rinse your decanters before you filled them? It's possible that musty odours or even soap residue could have imparted the off flavours you're talking about. Perhaps there are other readers out there who've run into similar problems. I'm curious.
The Flavour Principle by Lucy Waverman and Beppi Crosariol took home top prize last year for best general English cookbook at the Taste Canada Food Writing Awards. Published by HarperCollins.