I apologize if this has been discussed already, but has anyone tried to evaluate the impact on alcohol content on bottles that are 20 or 30 years old? I’ve heard that extended elevage can lower the ABV by up to .5%, so I assume that something similar could be true of extended bottle age, albeit more slowly (assuming normal cork performance). Perhaps the impact would be minimal.
Given the latitude many jurisdictions allow for ABV on labels, I imagine the only good way to measure would be to test the wine at bottling and then again in 20-30 years.
are you referring to angels share? I would imagine it is directly correlated to total volume loss since alcohol evaporates at a lower temperature than water it should increase over time but likely at a negligible rate
His question was “impact on ABV,” not “impact of ABV”
I’ve wondered the same. If fills go down because of evaporation through the cork and water and alcohol don’t have identical evaporation properties, then there ought to be some change in ABV over time, though I don’t know how significant it could be.
I’ve wondered the same thing. I believe alcohol evaporates faster than water, so if a bottle has ullage, would the alcohol level drop from what it was when it was bottled? It seems like it should to some degree.
Interesting. I believe William Kelley mentioned in a podcast that (paraphrasing from memory, which is always dangerous) one of the reasons he prefers a long time in barrel for his pinot is that it results in a wine that is half a percentage point lower in alcohol, which he prefers. I assumed the effect would take place through evaporation through the cork, albeit at a much slower pace. But perhaps I am misremembering the effect that William described.
I don’t know if there are any formulas for calculating the rate of drop, since, as others have said, a number of factors impact the rate of evaporation - there may very well be, I’m just not aware of any. But it is absolutely true that alcohol goes down, though slower in bottle than cask.
In spirits, it’s a very important change. We are an independent bottler of whisky, and have to test regularly while the spirits are still in cask to see where the ABV is, so we can decide when to bottle. At a certain point, even drawing a sample can reduce the alcohol - and with cask strength whisky, that can be a negative. This is why long aged whisky with high ABV is so unusual. The Glenfarclas 105 40 year famously clocks in at 60%, which is pretty astounding. It’s also pretty fantastic, but that’s beside the point.
This. Temperature has an effect on the rate of evaporation of both water and alcohol. Humidity has an effect on the rate of evaporation of water.
For example Vins Jaunes (that are systematically aged in oak barrels for 6 years or longer) develop very differently depending on if they are aged in the cellars (cool, damp) or in the attic (warm, dry). Wines aged in cellars are lower in alcohol, lighter in body and pale in color. Wines aged in attic are more concentrated, higher in alcohol, bigger in body and deeper in color.
Naturally there is also a spot in the relative air humidity where the evaporation rates are more or less identical for both water and alcohol; in this case the ABV of the wine remains constant and doesn’t change, even if the ullage gets bigger in the bottle or barrel.
It’s important to separate changes during barrel aging from changes during bottle aging.
The amount of evaporation that can happen during normal barrel aging can range from around 2% in a nicely controlled cellar to 10% over longer aging in a warmer or lower humidity cellar. In some very dry Californian cellars without humidity control (of which there are still plenty, especially in very small wineries), I’ve seen wines go to barrel at 15% and come out at 16.5%. In cellars with very high humidity, alcohol can indeed drop during barrel aging. I believe Randy Dunn claimed this as one of the sources of his lower alcohol levels, but it’s more common in more naturally humid places than California.
The amount of evaporation in a properly sealed bottle is very, very low, so the impact of aging on alcohol content should be minimal. If you have a very old bottle with a very low fill level, it’s possible that the alcohol content would have changed, but again this depends on the humidity of storage.
There was a winemaker in the Central Coast who left some of his wines in barrels for extended aging to raise the alcohol content (already distressingly high).
