Whisky & Oxidisation

Unlike wine, whisky doesn’t continue to mature after it’s been bottled but that doesn’t mean it doesn’t change. Oxidisation is great transformation tool, and one to oft overlooked by new whisky enthusiasts.

Spoiling Great Whisky

There are two great truths of the human condition;

  • We never want a good thing to end
  • Alles hat ein Ende, nur die Wurst hat zwei (German for ‘everything has an end, only the sausage has two’)

When an inexperienced whisky fan finds a spectacular new whisky they generally go through a three stages. They begin by prodiguously pouring and sharing. Then seeing the fill dip they share only with their closest friends, those deemed able to appreciate it. Finally they miserly pour smaller and smaller measures trying to put off the end of the bottle. Never more true if the bottle is rare, a lost gem. Unfortunately the whisky changes, the victim of oxidisation and inappropriate storage becoming something other than what they loved to begin with.


Happily oxidisation can easily go the other way, the finite shelf life or transformation of whiskey in combination with oxygen also have advantages. A whisky that doesn’t live up to expectations, rather than being used as fodder for an infinity bottling can be utterly transformed by exposure to oxygen. Longer term storage of an unloved whisky can make it not only far more interesting but actually create a new favourite. A certain Welsh whisky is becoming so well known among enthusasts for its transformation that we know drinkers who will deliberately decant the bottle to maximise oxidisation.

What is Oxidisation?

Oxidisation refers to the process by which a substance combines with or chemically reacts with oxygen. On a bike or car this is called rust, in a glass of wine this creates acetic acid (vinegar) and in a whisky it does something else again. While oxidation is an important part of the cask maturation process it also changes whisky in a bottled whisky once opened, causing gradual shifts in flavor and aroma. Bottles left open over time will slowly transofrm at a reate relative to the surface ratio.

Does whisky age in the bottle?

No whisky matures or ages only in contact with an oak barrel. The continual aging of wine in a bottle is related to tannin transformation – over time the tannins in a wine join together and form longer chains smoothing out the wine and imparting a silky smooth mouthfeel commonly associated with older reds. Assuming their is no cork/seal damage a still, unopened whisky will have virtually no contact with oxygen and so transform very little over time. Lacking the tannins, and organic material found within wine it will not continue to age, as such if your whisky was bottled at age 10, it will remain a 10 year old spirit. *In Scotland only Oak barrels may be used however other countries are less stringent and historically other barrels such as chestnut were allowed. **It should be noted that only a small number of wines actually benefit from bottle aging, the majority of wines produced are intended to be consumed quickly.

How long can you store whisky?

Once open a bottle of whisky, depending on fill level, can be stored for anywhere between 6 months and years. Generally the alcohol will begin to evaporate first making the whisky smother, then through ongoing changes with the active gas (oxygen) will transform the various flavour compounds in the whisky. In the short term this can improve the overall whisky, or rapidly deteriorate but the end result will always be the same, a lifeless, barely flavoured spirit. If you want to see this in miniature, leave a glass of whisky out overnight.

Storage Options Pro’s and Cons

There are a number of techniques used by whisky drinkers, most but of which will be covered here. Other tactics such as igniting the oxygen inside a bottle, or chilling the spirit are too dangerous, expensive or impractical to be worth recommendation.

Inert Gas for whisky preservation

Inert gas, that being any purified gas, such as argon, nitrogen or compound gas, which does not undergo chemical reaction is the Royce Rolls protection, in spite of this the cost is offputing towards all but the most serious whisky drinker. As these gasses are heavier than oxygen they will create a protective layer between the spirit and the air thus prevent oxidisation. Unfortunately as these require a top up after each pouring the use of gas can become quite expensive.

Decanting whisky in to smaller bottles

A simpler solution can also be to decant your whisky into a smaller container. If you’ve ever done a distillery tour and taken a drivers dram, or swapped samples then you probably have a few smaller bottles already. These can be bought wholesale on Amazon, at a pinch if you’ve properly cleaned a beer bottle, and kept a few corks you can decant your whisky into this bottle. Less air in the bottle, and a smaller surface area means less oxidisation. Ultimately this can be a nuisance as it means scanning through shelves of smaller bottles looking for a particular dram, not to mention the labeling but as a serious drinker you’re going to amass a collection of these anyway – and they’re very handy for new drinkers.

Vacuum pumps

Vacuum pumps are a great idea in theory though somewhat less so in practice. By using a pump you essentially suck the oxygen from the bottle leaving the liquid in a vacuum. If you’ve ever used these for your wine you’ll probably have noticed that they slow the deterioration rather than stopping it altogether. Unsurprising really as you won’t actually be able to remove all of the oxygen from the bottle, and oxygen is a gas so it will expand to fill the available space in the bottle. These will buy you time but not stop the process.

Sealing Bottles With Wax or Parafilm

You want your alcohol to last as long as possible unfortunately alcohol evaporates at a varying rate each year depending on temperature. I recently bought a bottle of Dallas Dhu at auction with a low fill level. This might not have been filled to the top of the neck, but this is the cost of evaporation. Add to this that as alcohol evaporates, bacterial contamination can become an issue, transforming your whisky into a milky or cloudy liquids that is both unattractive to look at and unappealing to drink the appeal is easy to see. Parafilm or wax are a great way of preventing anything from getting into your bottle, but they don’t do anything to remove the things already in there. As such they are a preservation tool, however if used on low fill level bottles they will not preserve it for long.

If you want to define the shelf life of a whiskey in more detail, you have to consider a number of factors. For example, it plays a major role whether the bottle is already open and how much has been drunk from it. Once the bottle has been opened, the whiskey is exposed to oxygen in the ambient air and slowly oxidizes. It can happen that the whiskey in the bottle loses both its aroma and taste.

You should therefore avoid ordering a good and possibly rare / expensive Dram in less established bars or restaurants, as the bottles here may be open in front of the shelf for a long time. Bottles whose filling level already indicates a longer opening time should also be avoided entirely. So the sediment is taboo as long as you don’t know that the bottle has only recently been opened. You can ask the bartender without obligation whether the whiskey is otherwise selling well …

If you want to preserve the original taste of a whiskey, opened bottles should not necessarily be left standing for more than six months. Especially not when there is more air in the bottle than whiskey. But if a whiskey is really good, you can probably enjoy the bottle within a few months. When in doubt, friends often turn out to be grateful buyers, even if they have little experience with whiskey. For a small private tasting, there are always curious people.

Once the whiskey bottle has been opened and simply does not want to be emptied, the bottle opening can also be sealed with Zelofan foil or sterile sealing foil, which is available in specialist shops or on the Internet, for a longer shelf life . This will reduce the ‘breathing’ of the bottle. You can also transfer whiskey residues into smaller bottles to reduce contact with oxygen in the bottle.

Unopened bottles, on the other hand, have an infinite shelf life, as the whiskey does not come into contact with sufficient oxygen here, which could significantly change its taste.

In general, whiskey should be stored in the dark or at least in a way that direct sunlight cannot affect it. You should also avoid moisture and heat during storage and keep the ambient temperature relatively constant. In contrast to wine, a standing storage of whiskey bottles is preferable, since the corks of a whiskey bottle do not close as tightly as those of a wine bottle - after all, the corks of whiskey bottles are designed to be able to close the bottle several times.

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