Okay tonight I bought a fresh bottle from Liquor Control Board of Ontario of Wray & Nephew White Overproof Rum. I am comparing it to a 30 year old bottle of the same brand which I bought in Jamaica in 1975. The oldie was stored in a cabinet in my home, half-full, well-sealed with its tin cap, and hadn't been tasted in many, many years.
The label graphics and information are almost exactly the same on both bottles. The only differences are the current bottle states the alcohol by volume (63%), omits the term "W.I." after Jamaica (West Indies) and is closed with a modern plastic twist cap. Otherwise the labels, down to the colours, are identical.
When I opened the new bottle a strong feinty smell rose from the lip of the bottle, EXACTLY as I recalled it from 30 years ago. It is a strong congeneric taste but not unpleasant. It reminds me of that hill country moonshine someone slipped me at the last Gazebo, that "wildflowers" smell that some grappas have, too. And it tastes like that, rich and spicy.
The bottle which sat 30 years in my house does not taste like that at all: it did 30 years ago but not now. The congeners are gone. The liquor is strong from the alcohol but smooth, like a good rectified white rum. It tastes, say, like a stronger version of Bacardi White Rum.
Clearly, the congeners disappeared over 30 years. Either they lifted off or more likely were converted by slow oxidation into innocuous-flavored compounds.
Unquestionably this proves to me that spirits age in the bottle in a manner similar to barrel aging. My memory is not fooling me.
I now believe we need to factor in the effect of oxygen on bourbon and rye kept in bottle a long time.
I now reject the theory that spirits don't change in bottle as a canard.