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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.