The question of how best to store your whisky comes up a lot in the whisky world. While the casual drinker may only have a bottle or two of different whiskies around at any given time, enthusiasts tend to collect quite a variety. Given the costs associated with some of these bottles, what is the best way to store them to ensure minimal change in the flavour over time? There are a lot opinions available online – some of which actually run counter to evidence. So let me walk you through the best evidence-supported recommendations.
This article has been updated twice, with new links provided for additional studies, as described below. Latest update was March 31, 2020.
1. Sealed bottles (i.e., new and unopened)
For sealed bottles, the answer is fairly easy – store your whisky upright, in a dark (and preferably cool) place, minimizing light and temperature fluctuations. I’ll explain each of the reasons below.
1.1. Keep Them Upright
Upright is most important, as the high proof ethanol in whisky will degrade the cork over time if stored on the side – dissolving the cork, and tainting the flavour of the whisky. This comes as a surprise to most wine drinkers, who are always advised to keep wine bottles on their side. But that is because wine is much lower proof (lower alcohol content relative to water), and so the water in wine keeps the cork from drying out. This is important, as a dried-out cork will let air in, spoiling the wine. Unopened whisky bottles are fully sealed, and the contents do not change in the bottle so long as they stay sealed and well stored.
I’ve seen comments online about “moistening” the cork periodically in whisky bottles (by temporarily tilting the bottle on the side). This does nothing of the sort, as the higher ethanol content is actually drying out the cork. But periodic contact of the whisky with the cork is not likely to harm it much – after all, this happens all the time when a bottle is handled or shipped.
On that point, I routinely pick up bottles in my travels, and pack them in my checked suitcase for return travel. I have never had an issue with cork leakage in new, sealed bottles. Where you will get into trouble is with open bottles that are only partially-filled (as the extra air contracts and expands with pressure changes at altitude, causing the cork to pop out – more on this later). Note that minor leakage can occur with some screw caps enclosures, even if the seal is unbroken. Air pressure changes can cause small leaks as there is “wiggle room” for the cap to loosen slightly. You will want to give screw-caps an extra hand-tighten to make sure they aren’t loose to start, and encase the bottles in sealed containers. I use extra-large Ziploc freezer bags, and they do well to capture any minor leakage. One exception to placing whisky in checked luggage is for smaller planes (used for short hops), where the cargo hold may not be within the pressurized cabin area. For any jetliner, you won’t have this concern, as the cargo holds are all pressurized.
Your bigger risk traveling with checked bottles is breaking at the neck point, due to rough handling of your bag. So always make sure they are well-wrapped in clothes or bubble wrap (I find laser toner cartridge shipping bags great for this, with a pair of socks wrapped around the bottle neck). Also try to pack in the middle of the suitcase, not near an edge.
1.2. Avoid Natural Light
Many studies have shown that sunlight is one of the biggest threats to whisky (some links provided below in my discussion of open bottles). Even indirect natural light will induce changes over time, so you are best storing your whisky in the dark – like in a cupboard with doors kept closed. Keeping them in their cardboard boxes/tubes will also help in protecting against light pollution. But I’ve also seen suggestions to ditch the cardboard boxes if you are planning for very long-term storage (i.e., decades), as the cardboard/glue can become a substrate for microbial/fungal contamination. But that only matters for the serious collector (who likely has a proper climate controlled dark environment for their whisky anyway).
UPDATE 03/31/20: The final 24-month analysis by Breaking Bourbon on open bottles found that direct sunlight did indeed significantly effect the taste of bourbon. Note that this effect was additive with air exposure (i.e., bottles with more headspace showed greater degradation). Scroll down for further studies looking at air exposure in open bottles.
1.3. Avoid High Heat and/or Temperature Fluctuations
Cool storage is better than warm, but fluctuations in temperature are potentially even more of a concern (again, see some of the links below for studies on open bottles). A fascinating story is the discovery of century-old crates of Scotch whisky in the Antarctic permafrost – as recounted here. The whisky was apparently still in excellent shape. Actual storage temperature probably doesn’t matter much, as long as it is not higher than room temperature – and so long as it reasonably stable (i.e., not in your attic, or next to your furnace!)
2. Open Bottles
Once opened, whisky can start to show age and exposure effects in the bottle. This is a different sort of “aging” than what happens in the barrel during whisky production, which is necessary to make whisky (see my Sources of Whisky Flavour page for more info). How noticeable these changes may be is an interesting question – and one that I will return to in section 3 after I describe the results from a number of interesting studies below.
The common concern here is due to the increasing presence of air in an open whisky bottle.
As an aside, it is a pet peeve of mine that most people refer to this incorrectly as “oxidation.” Oxidation refers to a specific chemical reaction that involves a transfer of electrons between chemical species (specifically, the stripping of electrons from the chemical that gets “oxidized”). Given the high proof of whisky, classic oxidative reactions at the air-liquid interface in bottles are unlikely to be contributing in a major way to changing characteristics over time (a fact borne out by empirical testing).
Furthermore, there are actually two separate issues potentially at play here – the repeated air exchange each time you pour a dram from a bottle, and the expanding volume of air in the bottle over time.
You might not have thought of the first one, but it seems a lot more likely that it is not the new air going into the bottle that is having any effect, but rather the repeated escape of the headspace air moving out of the bottle (i.e., the air exchange). The reason for this has to do with vapour pressure in a bottle – ethanol is more volatile than water, and so (in gas form) takes up more of the headspace. Every time you pour a dram and exchange the headspace you are effectively diluting your whisky minutely, by effectively increasing the relative amount of water to ethanol inside the bottle. The same could also be true of the aromatic compounds that give whisky its smell and taste. Basically, every time you exchange the air, the headspace refills with higher volatile components from the liquid – which then get depleted on the next pour, starting the whole process all over again. And over time, the volume of that air headspace in the bottle keeps growing, accelerating the pull-out of volatile molecules each time it is replaced. At least in theory, this could lead to a reduction in flavour over time.
But is this really a concern in practice? Unfortunately, the academic literature (which I have reviewed) is not too concerned on this point. The few studies done typically explore these questions from a theoretical perspective, under acute laboratory conditions with specialized preparations that don’t reflect long-term use or storage concerns of open bottles. But there are a number of whisky enthusiast/citizen scientist experiments that are worth considering here (including some with analytical testing). At the end of the day, it is empirical observations using sensory analysis (i.e., tasting with blind tasters) that is the best way to compare the effects of potential storage conditions on perceived flavour.
As previously mentioned on this page, at least one whisky enthusiast study has suggested open bottles with greater air headspace show more advanced degradation when exposed to sunlight. But what about properly stored open bottles? Cited below are a small study by Mattias Klasson of scotchwhisky.com, and a more rigorous and detailed study by Marcus Fan. Both of these studies found noticeable effects from large air volumes over time, depending on the storage conditions.
UPDATE 12/23/19: The Fan website appears to be down, but you can use this link to see the last saved way-back-machine cache of the site. Alternatively, you can download a copy of the Fan study here, in plain-text format. You may also find the Scotch Test Dummies test mentioned in the comments below interesting as well. While that last example wasn’t done blind, the examiners were clearly surprised by the result (i.e., expected the opposite finding).
Before I get into each of their specific testing results, a brief explanation of popular storage options for open bottles of whisky is presented below (many of these are tested in the individual studies linked to above).
2.1. Leave Them Alone
The first option is to simply leave the whisky in the well-capped bottle until it is gone. But a popular belief online is that the air-induced changes in whisky intensify once the bottle has dropped to less than half volume – and becomes extreme once only a small volume is left (i.e., only a “heel” of whisky left in the bottle). This would be consistent with the headspace air-exchange line of reasoning provided above. So practically, you probably don’t even need to worry until you pass the point where there is more air in the bottle than whisky.
A related question comes up about storing whisky in crystal glass decanters (for display purposes). Here again, the indirect light issue comes into play, as you will degrade the whisky over time (even faster than you will from the air). Even worse, those clear crystal decanters are actually lead crystal. The high proof alcohol in whisky will gradually extract lead from the glass, dosing you with something you will definitely want to avoid.
So what can you do to minimize air effects once the whisky volume drops substantially? Here are the most popular options:
2.2. Use Smaller Glass Bottles
This is probably the most popular option in the whisky enthusiast community. To minimize air headspace, simply pour the whisky into smaller glass bottles. Commonly available are Boston round bottles in 0.5, 1, 2, 4, 8, and 16 oz sizes. These are available in clear glass or, better yet to minimize light effects, amber or cobalt blue glass. The results of the Breaking Bourbon, Fan and Klasson studies support this method as one of the best ways to minimize air effects.
Bottles caps matter here though. The best bottle enclosures are phenolic screw caps (made from black polypropylene). But do not use the cheaper ones with paper liners. Instead, use only polycone liners (see attached photo comparison).
The cheaper caps use pulp paper with a thin polyethylene coating, and are intended for aqueous solutions only (i.e., pure water-based). These will degrade rapidly in direct contact with high-proof alcohol fumes. You will soon find the liner contents dissolving into your whisky, making a disgusting mess. I’ve seen this happen to a few sample bottles I’ve received in swaps with other reviewers, when I didn’t check the caps (for samples I didn’t get to right away). Polycone liners are conical-shaped liners made of an oil-resistant plastic – and are designed to resist chemicals, solvents, oils, etc.
This decanting approach into smaller glass bottles is the consistent first choice across all studies for long-term storage. My personal experience also supports this conclusion.
As an aside, a cheaper alternative is to use clear plastic PET (polyethylene terephthalate) bottles. While it is true that some bottom-shelf whiskies come in PET containers (along with many other food and liquid stuffs), the long-term effect of storage of high-proof alcohol in these containers is unknown. It is reasonable to worry about the potential extraction of plasticizers over time (i.e., the additives used during production to keep the plastic from becoming too brittle).
At a minimum, it would be important to ensure you are getting food-grade PET bottles, with proper polycone caps. In the Klasson study, they use “cheap PET bottles” (source not identified), and found a significant change in flavour over time. I’ve kept whisky in food-grade PET bottles for up to 6 months, and have not noticed any off flavours. But I would consider this a riskier proposition, and recommend you stick with glass bottles if at all possible.
2.3. Fill Up the Original Bottle with Glass Marbles
A seemingly ingenious solution to the air volume issue is to pour glass marbles into the original bottle as the whisky volume drops, thus minimizing air headspace. Sounds reasonable, right? Except this approach means that you are greatly increasing the whisky-to-glass ratio over time, especially as the volume drops. All that increased glass surface area is an opportunity for interactions to occur (i.e., there is more surface for the congeners and other flavour molecules in the whisky to “stick” to).
At a minimum, you would need to ensure the marbles were scrupulously cleaned and sterilized before use. And I have no idea where you would get food-grade glass marbles to start with – children’s toy marbles are not likely to be made of high quality glass, and are likely to contain various contaminants that could leach out in the presence of high proof alcohol (e.g., lead). Conducted properly though, this approach is likely to work – as demonstrated in the Fan study. But I think you are best to decant into smaller glass bottles.
2.4. Neutral Gas Spray (e.g. Wine Preserve)
This is a popular option for those coming from the wine world. Indeed, I frequently see this recommended in online whisky forums – but one that I must caution against using.
The principle is that an inert, neutral gas like argon (Ar) can be sprayed over the surface of the liquid, thus preventing the lighter-weight oxygen (O2) from reaching the wine (or whisky) once re-corked. There are various “wine preserve” brands out there, each with their particular (and often undisclosed) blend of argon, nitrogen (N2) and carbon dioxide (CO2).
Keep in mind, these sprays were all developed and tested on wine – it is unknown how the much higher proof whisky would react. One obvious concern is that the lower-proof wine “preserved” this way was only meant to be kept for up to a week or two. Long-term storage effects (typically months to years) for high-proof whisky are thus largely unknown.
A potential problem here is that the spray canisters need a food-grade aerosol propellant in order to eject the “inert” gas down the long extended tube into the whisky. In the old days, this was Freon – but that has since been replaced by butane and propane. It is not at all clear what the long-term effects of adding butane/propane, as well as Ar/N2/CO2, inside a whisky bottle would be. The chemistry that occurs at the air interface of high-proof whisky is complex and not fully understood – adding these extra variables would be a concern.
Indeed, in the study by by Fan, the most popular neutral gas spray – Private Preserve Wine Preserver (shown above) – consistently induced greater flavour change than any other condition beyond indirect sunlight (!). While exposure to regular air had noticeable effects when the whisky volume was very low (e.g. 150 mL in a 750 mL bottle), these were almost twice as noticeable when wine preserve spray was used. Simply put, wine preserve was considerably worse than just regular air exposure in a bottle. See also these (unblinded) results from the Scotch Test Dummies.
On the basis of these findings, I strongly recommend you do NOT use neutral gas sprays in your whisky bottles.
2.5 Vacuum Seals
Another popular option from the wine world. Typically, a specialized rubber cork is placed at the opening of the wine bottle, and a hand pump is used to extract most of the air from the bottle (creating a partial vacuum). I’ve used this myself, and it does help keep wine flavourful for a few days (compared to simply re-corking).
For whisky, there are two main concerns. For one, the seal will not last over the longer term, and the high-proof ethanol is likely to degrade the rubber gaskets over time. I’ve not seen a whisky study done using wine bottle vacuum seals, but the Fan study did look at placing the small sealed whisky bottles in standard food vacuum sealer bags. Their results showed no net benefit to this whisky using this method (and I wouldn’t have expected any).
But the more important point is that a proper vacuum seal on a bottle would be expected to increase the pull of ethanol and other high-volatile aromatics out of the whisky over time, as explained here. If effective dilution of the whisky is the end result of repeated air exchange, vacuum seals would be expected to make this worse.
Either way, I recommend you stick to storage without the vacuum seal complexity.
A standard in any chemistry or biology lab, Parafilm is a thin plastic film of paraffin wax. Paraffin is a soft, colourless wax used for making candles and crayons, among other things. Parafilm is used in labs to temporarily seal an open container (like an Erlenmeyer flask), or for longer-term storage of lidded containers (where are you are trying to prevent moisture or air contamination).
While Parafilm can certainly be degraded by various chemical solvents, it is relatively resistant to ethanol. Unfortunately, Parafilm is still relatively gas permeable, so it is best suited to serve as physical barrier for liquid penetration, not gas phase exchange.
I personally use it when transporting whisky – especially when carrying sample bottles on airplanes. The pressure changes are likely to cause leaks, and Parafilm is very helpful in minimizing these. But as a way to preserve whisky in the bottle, it likely only of minimal effectiveness – and therefore probably not worth the effort.
3. Do Detectable Changes in Whisky Really Occur, and if so, Over What Time Frame?
Much of the preceding section was predicated on the common belief that whisky changes over time, and that these changes are noticeable to a whisky drinker. Indeed, the testing experiments described above by Breaking Bourbon, Marcus Fan and Mattias Klasson all demonstrate changes over time that were detectable by experienced tasters blind to sample conditions. Of course, the magnitude of those effects were highly dependent on the specific controlled storage conditions examined. So the real practical question is, how much of a change are we really talking about inside a typical open bottle left corked on a shelf?
In this regard, two more recent studies are helpful. Both Wade Woodward and the British Bourbon Society did proper blind triangle taste tasting for existing bottles. This is actually the same method used by whisky makers for minimizing batch variation across establishing bottlings, as I describe on my Single Malts vs. Blends – Understanding Whisky page (please see “How Consistency is Maintained Across Batches in Scotch” for more background).
For these two studies, two identical bottles from a common batch were used for comparisons – one that had stayed sealed, and one that was opened, experienced repeated samplings, and then left for a period of time corked with reduced volume (i.e., significant air headspace). A blind panel of experienced tasters was presented with three identical-looking samples in a triangle test format – two samples from one bottle and one from the other. They do not know which is which, and are asked only if they can identify the “odd one out” from the array (i.e., which sample is different from the other two).
In the British Bourbon Society study, with one bottle that had been open for half a year, only two of the six blind tasters correctly identified the odd one out. That is exactly the result you would expect from random chance alone, when asked to identify one out of three samples. And incidentally, those two correct reviewers both found the opened bottle to have more flavour, not less. In the Woodward study, not one of the ten blind tasters correctly identified the odd one out for a bottle that had been open for one year. And yet they all believed they could tell a difference – they were all wrong, even though they were actually given the option of reporting no observed difference in that study.
Both the BBS and Woodward studies followed up with analytical testing of aroma molecules in their bottles; Headspace Solid Phase Microextraction (SPME) followed by Gas Chromatography in the BBS study, and Gas Chromatography – Mass Spectrometry (GC/MS) in the Woodward study. Both of these tests can measure molecules down to level of parts per million. Both found virtually identical patterns for all molecules detectable in both the old and new bottles (and dozens of individual molecules were detected and measured for each bottle). There was no measurable difference in the levels of any of the major species they could identify.
Taken together, these studies call into the question whether air-induced changes inside a whisky bottle matter over the six month to one-year time frame.
4. Interim Conclusions
Based on the evidence to date, you will want to keep your whisky upright and in the dark (preferably in a consistently cool place). But you probably do not need to stress too much about any potential air exchange effects over the short term (i.e., under a year), or for bottles that are still more liquid than air.
If you want to ensure the flavour profile remains as consistent as possible for open bottles over a longer term, your best bet would be to decant into small glass bottles with proper polycone caps, taking care to minimize any air headspace. Just about anything else brings with it potential risks, and either lacks evidence of effectiveness (e.g., vacuum seals), or has clear evidence of negative effects (e.g., neutral gas sprays).
I hope you found the above useful. I’ll update this post if any new studies come out that I think are of particular relevance.