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Barrel Aging 101

edited July 2023 in General

Barrel aging 101.

I promised that I would write this a little while back and I have received a couple of questions about barrel aging lately so here it is. I have tried most process for accelerated aging and I have come to the conclusion that there is very little that can be done to accelerate aging and quite honestly if you want a very high quality product you need to just have patience. The following description are the basics for beginners as well I will say what are my results.

The basics of barrel aging are that the process or aging involves a number of chemical process that require oxygen, and some that don’t. The aging process that take part are in wooden barrels require both the aerobic and anaeorobic reactions to take place. Oak barrels due to their molecular structure a slightly porous longitudinally and ever so slightly porous tangentially. This means that fluids move in and out of a sealed barrel albeit at a very slow rate. The rate of a liquid, or spirit, moving in and out of the wood depends on the base temperature of the liquid and the overall thermal range of temperature to that which the barrel is subject. An alcoholic spirit produces ethanol in vapor which is highly expansive and responsive to heat. Far more so than water. So when a barrel with a spirit inside heats up this produces ethanol in vapor. This ethanol in vapor creates a positive pressure inside the barrel which forces the spirit into the wood.

In his way oxygen that is coming through the wood interacts with the spirit inside the wood and produces chemical reactions with compounds found inside the wood to produce flavor compounds. When the temperature cools down this creates a partial vacuum that sucks the spirit out of the wood and with this it brings the flavor compounds created inside the wood. It should be noted that many of the flavor compounds are created in the process of toasting the barrel when the barrel is made. Barrels are toasted at different temperatures for between 120 to 180 minutes. Different durations of heating produce different flavors as well as toasting the inside of the barrel. The toasted or charred texture helps “filter” the flavors in the spirit as they go in and out of the wood.

OK as can be seen basically Barrels are “breathing” as the heat up and cool down. So what controls the rate of their breathing. The very simple answer is the thermal temperature range withing a day and over an yearly period. For example in Scotland the ambient temperature is between 5 to 15 degrees average year round. Summer will get up to 10 to 20 C and winter will be -10 to +5. In Tennesee for example the temperatures swings can be very large, ie between 10 deg at night to 30 in the day. Where I am, which is the mountains of Argentina we can have 20 to 30 degree temperature swings. As well too another determining factor is how the barrels are stored. In very large rick houses or barrel rooms hold thousands of barrels or hundreds of thousands of litres of spirit it can take days or weeks to change temperature. I once watched a video of a Scotch Producer that said in their large barrel houses that hold 10,000 barrels of 220 litres it takes 5 days to change the temperature of the whiskey by just 1 degree C. Why does this matter ? It means that this whiskey is barely moving in and out of the barrel and moves very slowly over an annual basis. The Scottish distillers are Ok with this as the older it gets the more money they get, and theoretically you get a better product.

So that’s how it works. Now can you accelerate process ? There have been many posts written on accelerated aging, as well as many posts on this board. I have tried them all. Ultrasound with toasted lingots got the closest to something that worked but quite frankly none of them came close to the same quality of product you get from a properly aged whiskey out of the barrel. Now there are somethings you can do that are effective. The one thing is go for a smaller size barrel. Aging rates are determined by surface area to volume ratio of the barrel. The larger the barrel the less surface area per litre that the spirit is exposed to that is “breathing” 20litre barrels age very quickly, 50 litres less so, 100l even less and then up to 220l barrels.

So the starting distiller might ask what is the best size to use. The problem with the smaller barrels is that they age very quickly. I have had a 20l whiskey age out in 2 months

I should say here I learnt very early on is that if I have my barrels undercover in my shed where there is little temperature swings the aging was very slow. So put them in my gallery where the indirect light in summer and direct light in winter and I get very fast aging. For example getting indirect light I am aging out 200l barrels in about 3 months. Inside the barrel the temps are getting up to 40 deg C during the day in winter where and at night they get down to 5 deg C.

So what about the angels share. Yes with this kind of accelerated aging the angels take a piece. Normally in Scotland they calculate the angels share is about 2% per year. Here I can get between 4 to 5% losses in only 3 to 5 months. For the beginners the angels share is the loss of volume that takes place inside a barrel as it is breathing. In high temperature and dry environments this loss is mainly ethanol and in wet moist and cold environments, like Scotland, its mainly water. Now in a lot of countries you have to account for the losses to your regulator authorities. That is not so much an issue if your just a home distiller or where I am the regulatory authorities are not as vigiliant about those things.

So what is the best time to pull the whiskey off the wood ? The answer is when the whiskey maker wants it to be so. But the second answer is when the whiskey flavor is about to be overcome by the wood. Each whiskey maker should have in mind what kind of flavor profile you want to create in a given spirit and that includes how much barrel/wood flavor you want in a wood. For example if your making a light Irish whiskey you want either a soft French oak finish or a sherry barrel finish. If your making a full flavor stout whiskey you want a medium American oak finish. If you making a full blooded rye then its first use American oak. It becomes a very personal thing. I have been asked about what types of whiskeys to make recently by a few guys and I always say. Go out and buy a couple of different, Japanese, Irish, Scotch and American style whiskeys and try them all. Try different grains and figure out what you like and what you want to make. Then figure out what type of barrels they use and use those type of barrels. What is most important if your making whiskey is to keep testing it. I know it’s a tough job. This is one of those things that the only way to train your tongue is to keep training it and keep trying the same spirit or many in the barrel to know when its ready. I always pull it a bit early just because there is very little you can do if a whiskey is overwooded. Earlier this year I had 800l of whiskey in 4 barrels that I laid down in January and I didn’t test them until the end of March. During this time it was very hot here, like 20 deg C during the day and 45 C at night. When I finally tasted them they were all overwooded. So I have been able to blend down 3 of them. In order to blend out an overwooded whiskey you have to make the same whiskey and pull it early then mix it with the overwooded whiskey to soften the wood taste.


  • edited July 2023

    So the next point is if you put your barrels in a high temp swing location you get this very accelerated aging. But this accelerates the aerobic reactions and not the anaerobic reactions. These will take place in the bottle. In Scotland, for example, the anaerobic reactions take place when its below zero and the whiskey isn’t moving in or out of the barrel at all. What I am doing is I pull the whiskey when it has the color and flavor that I want, which depending on the season is between 3 to 6 months, then I bottle it and leave it for between 6 to 12 months. There is a marked improvement after 6 months and very great improvement after 12 months. After 2 years they are getting flavor profiles and smothness of whiskeys 12 to 15 years old from Scotland for example. Experienced whiskey tasters cant tell the difference. I had a woman come over to my house once and she was the head taster for Seagrams for 10 years and she thought my 12 month old whiskeys tasted like 10 year olds.

    So, the next question is at what ABV should you barrel? This question has been answered a couple of times on this forum. But in my experience I barrel at 51%. If its going to be hot I jack the whiskey with another 2 to 3 of percent of pure ethanol, which is illegal in some countries. This is basically paying the Angels up front in ethanol. If you look at historical data up until the 1920 almost all whisky was barrelled in both Ireland, Scotland and the US at 100to 110 proof, or between 50 to 55% ethanol. The Irish tended closer to 51%. I have barrelled whiskey between 40 to 65%. As a note of caution you should never barrel a sprit below 45% and part of the reactions at that ABV produces methanol. And there is nothing you can do to get it out of there. I did that a couple of times and all I could do was give it away to my gardener mate who sold it to his mates to mix with cocacola. A sad end to a couple of fine single malt Smoked barley whiskeys.

    With your whiskey barreld at 51% you get the best idea of how a whiskey is aging and what will be the final flavor profile. So why do the big distilleries age at 60 to 65? The answer is volume. If your producing thousands of barrels worth of whiskey a day the difference from 50 to 65 % is actually 30% more. Ie 30% more barrels, 30 % more barrel rooms, 30% morebarrel handling etc. For big distilleries it really adds up. For smaller distilleries and home spirit makers if you can, you should barrel at between 51% to 55%, especially when your training your palate to detect the advancing aging of your spirit in a barrel.

    One more final point never let your barrels get damp or wet. At least not if you can avoid it. If a barrel gets a fungus infection it produces an off flavor that you cant get rid of.

    So the key summaries are the following:

    • Different barrel sizes age differently. The smaller the faster.
    • The best way to accelerate aging is to have higher temperature swings of the spirit in the barrel.
    • If your using smaller barrels you should taste your whiskey almost every week and pull it early.
    • The best ABV to put your spirit in a barrel is between 50 to 55 deg C.
    • There is very little you can do if a spirit is over-wooded. Try to blend it out.
    • If you get accelerated aging using the above techniques you need to store your bottles for a long period of time to allow for the anaerobic reactions to take place.
    • Every location is different and the most critical aspect is the thermal range you get in a given day and over a year.
  • Good stuff mate.

    You mention pressure in the barrel, but remember that atmospheric pressure changes also come into play, especially in areas that are prone to big weather events like the "southerly" changes that sweep through the southern half of Australia with the corresponding temp and pressure drops.

  • edited July 2023

    Part 3. I just forgot a couple of points,

    How many uses can you get out a barrel? Well this depends on the barrel and if it is a first use or not. Where I live I can get cheap refurbished french and american oak barrels that are very cheap and very good.

    The rule of thumb is you can get 4 uses out of most barrels although in my experience the first three are good and the last one can be hit and miss. As I said I use refurbished barrels that are often former wine barrels that were shaved and toasted to my requirement, so you really dont get a lot of the fourth use. Although I do have some fresh, ie zero prior use, Lenga barrels that you get a decent 4th use out of but thats the exception. If you have a barrel that is on its 4th use and your not getting a lot of flavor and color out of it, the spirit will keep getting better but it wont be picking up the color and flavor that you need. In this case there is nothing to do but to take it out of that barrel and put it a new barrel.

    If your using refurbished barrels you do get some flavors from the previous liquid that was in there. For me I have used a number of 100 and 200l french oak barrels that were used with various white wines. Most are good but every now and again you will get a barrel that produces an exceptional finish. I had one that had had an excellent chardonnay in it that gave an amazing finish to a light Irish whiskey. The main problem you have as a small distillery of home distiller as your not buying barrels in bulk and so the barrel notes will vary depending on what was in the barrels before. It pays to get to know your cooper. On the toasting process I wont go into that a lot here but I have tried toasts from 1 through to 4. In my opinion barrels should be toasted to number 3. The few times I had a barrel toasted to 4 they were just blasted to shit and the whiskey aged but the flavor from the wood was almost non existent. In those cases there is nothing you can do put pull the whiskey from the nonperforming barrel and put it in a new one.

    So how much does barreling cost ? Leaving aside storage space it depends on your barrel purchase Price. I figure I can get about 300l use out of a 100l barrel. I pay about US$80 for a 100l barrel and about US$95 for a 200l barrel. You can get about 600l use out of a 200l barrel. As I said earlier I retire barrels when they get to 3 uses, except for my lenga barrels. Those are about US$200 for a 100l. The above barrel prices are about 1/5 of other places but I live in a wine growing province and there is a huge industry supplying wineries with barrels. What happens is they import the wood, make the barrels, sell them to the big wineries, they will uses them generally for 7 to 12 months for their high end wine. In which case they are sold for pennys on the dollar back to the copper and the coppers make money by resizing and refurbishing them.

    So how do you get to know the differences in barrel flavor ? Well there some guides out there about what the differences are but I would suggest for a beginner to buy 4 or 5 different whiskeys with different barrel notes and then try them all side by side. In these cases I would say go for a light Canadian whiskey to try light north american oak. A full blooded bourbon for heavy american oak. Greenspot Irish for sherry oak barrel finish, Red breast or teelings for a light french oak finish. I have actually made whiskey with Slovenian oak and Amburana which is a south American wood. They all have their own distinct profile. As well too when I was in Armenia I tried a Georgian wine that was made with a Georgian oak barrel and it was fantastic. The wood profile was somewhere between a French oak an American Oak.

  • edited October 2023


    I may have understood something wrong here, but I was under the impression that Scottish barrels loose ethanol (as moist environment prevents water evaporation) and Tennessee barrels loose water (dry environment promotes water evaporation) and gain alcocholic strength , but you say it's the other way round?

    How Location in a Distillery Rackhouse Effects Proof @ Distillery Trail

    P.S. Over in my neck of the woods a large distillery set out to produce a single malt . They have 7 variations, some of them aged in red wine barrels. Haven't tasted those yet but I hear they were good, so maybe think about using a winery barrel straight after it was emptied.

  • Few of us have done that here in Australia. Seppelts do a deal where they sell 80 or 100l one use barrels from Octavia. I bought a pallet group buy a few years back.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • I tried that once. Sorry it doesnt work. The barrels need to be charred to get some of the flavor compounds that you want. That being said most of the barrels i use are ex wine barrels. Some of the best i had were onrs that had very good chardonnay in them. A light irish whiskey or pilsen base whiskey and you could get a very light buttery chardonay flavor in the whiskey.

  • Works good on rum too, most of us went rum first use to get the real ruby colour out before going for bourbons or whiskeys.

    It works very well, but it is a different flavour to a heavy char barrel is all.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • edited October 2023

    Did not love ex-wine barrels standalone.

    I can see that end result being used as part of a blend. Makes perfect sense as a secondary/finish cask.

    That said, I hate tannin, abhor. I also feel that some of the acids in wine (malic), reallly don’t pair well with whiskey or rum (sopping wet fresh dumps).

    Aging rum in one of these with a high barrel entry proof? My worst nightmare.

    Will take vanilla and caramel all day long over sour fruit and sandpaper.

  • I agree. I only tried it once and that was because i got a used malbec wine barrel for free. Never again. White wine barrels that are shaved and toasted csn give very nice notes to a light single malt. Red wine barrels nope.

  • A lot of Aussie distillers are using ex wine barrels as they are cheaper and more easily available here. That said I agree that red wine cask whisk(e)y or rum isn't to my taste. Like @DonMateo says, I've tried some nice product out of ex white wine casks eg toasted ex chardonay.

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