Two new 1 liter whiskey barrels for my imperial stout

So I have a friend who ages his own small batches of whiskey. Since he wants to make them in the bourbon tradition, he uses them once and then can't use them again. Good deal for me.

So per advice from this forum, I made a stout for my first attempt with these barrels. Because these barrels are so small, I intend to oak two liters of the batch and then blend it back into the main batch. The big question is, how long do I need to age the two liters in order to pick up enough oak/whiskey flavor for the whole five gallon batch. I did some calculations, made some assumptions and came up with a number, but I'd like you all to check my assumptions (and my math if you don't mind). So, here we go:

If I want my beer to develop a particular flavor profile, I will have to over-age the small amount of beer I put in the barrels to get that flavor profile.

In order to get my 5 gallon batch to taste like a commercial beer might after being aged 6 months in a 53 gallon barrel, I did these calculations:

53 gallons = approx 200 liters
6 months = 26 weeks = 182 days
200 liters /182 days = 1liter /x days
To solve for x, you cross multiply.
200x = 182
Divide both sides by 200 and you get x = .91 days

So, to oak 1 liter it would be about 1 day to get the flavor profile commercial brewers get in 6 months of aging in a 53 gallon barrel. It would be 2 days to get a 1 year age effect.

This assumes that the rate of oak/whiskey flavor is a direct ratio with size of the barrel, surface area to beer, etc.

Now, to get the 5 gallon batch to taste like 6 months of aging I have to over oak the two liters. in order to get the desired flavor profile for the whole batch, for which i will use the number 100 (as in 100%), I have did these calculations:

2 liters at .91 days = 100%, but I have 17 more liters at 0
Once I mix them, the mixture becomes diluted.
2 liter /19 (whole batch)= .105
.105 times 100 and you get 10.5%
10.5% if aged .91 days. How many days?
10.5% / .91 days = 100% / x days
10.5x = 91 Divide both sides by 10.5 which gives me 8.6 days

Now, I know that every barrel will age differently and each beer will hide or show oak/whiskey flavors differently. But this could give me a guide for how long I would need to age the beer in the barrels as long as my big assumption about the direct ratio of size to time in gaining oak flavor.

What do you think?

I think that calculation is a great start. I would suggest that instead of using liters/days as the unit to convert, you use the unit liters/(area days). where area is the inner surface area of the volumes, because afterall, the amount of oak flavor the beer gets is directly related to the area/volume ratio of the barrell. This would probably alter your series of calculations little, but be more accurate:

53 gallons = approx 200 liters
6 months = 26 weeks = 182 days
Surface Area of 53 ga barrel = SA1
Surface Area of 1 L barell = SA2
200 liters /(SA1 182 days) = 1liter /(SA2 x days)
To solve for x, you cross multiply.

x = (SA1/SA2) * (1 L/ 200L) * (182 days)

Now, I'm not sure about the surface area of each of the barrels, but I'd say with some googling you could probably come about it somewhere.

Taste is really the superior standard. For five gallon barrels it's said three weeks is sufficient time in a used barrel. With smaller surface space I'd say you need to start tasting it after a few days, certainly no longer than a week. Just take a small amount from the barrel and some of the non-barrel and mix in the same proportions as the final beer. When it reaches the right flavor it's time to bottle.

I will freely grant the possibility that I am totally mistaken, but I'm guessing that the flavors you get from extended aging are different (i.e., not just more intense) than the flavors you get from short-term contact. Were they not, I would think bourbon manufacturers would use tiny barrels for a year instead of enormous ones for 18 years. I think the total time you would want to age would still be 6 months or whatever, and that the extra flavors during this time would then be spread throughout the 5 gallons of beer. Aging time is also greatly impacted by temparature and temp fluctuations, more fluctuation speeding things along.

The surface area of the barrels is easy math. The top and bottom are each Pi multiplied by the radius squared. The side of the barrel would be Pi x diameter x height, except that the barrel bows out in the middle, so sub 4 for Pi as a back-of-the-envelope type calculation. Of course, you don't have a 53 gallon barrel to measure.

KBentley57 said:

I think that calculation is a great start. I would suggest that instead of using liters/days as the unit to convert, you use the unit liters/(area days). where area is the inner surface area of the volumes, because afterall, the amount of oak flavor the beer gets is directly related to the area/volume ratio of the barrell. This would probably alter your series of calculations little, but be more accurate:

53 gallons = approx 200 liters
6 months = 26 weeks = 182 days
Surface Area of 53 ga barrel = SA1
Surface Area of 1 L barell = SA2
200 liters /(SA1 182 days) = 1liter /(SA2 x days)
To solve for x, you cross multiply.

x = (SA1/SA2) * (1 L/ 200L) * (182 days)

Now, I'm not sure about the surface area of each of the barrels, but I'd say with some googling you could probably come about it somewhere.

Click to expand...

Wouldn't it be more like (SA/liters)/ Days? I think you're looking for surface area per liter of beer.

So (SA1/ 200 liters)/ 182 = (SA2/ 1 liter)/ x days

kingwood-kid said:

Were they not, I would think bourbon manufacturers would use tiny barrels for a year instead of enormous ones for 18 years.

Click to expand...

I've read that many small distilleries are using small barrels and again them for short times in order to sell their products faster. There's a debate whether that kind of aging will produce the same quality as the traditional bourbon makers.

I like the mathematical approach of KBentley57's math, but I don't see why you need to consider a full size barrel, if you have only two 1 liter barrels, and a 5 gallon batch of beer. Besides, a Barrel is a generic term, as there are different size barrels. Do you mean the 55 gallon barrel?

But I have to agree with ReverseApacheMaster.

The only surefire way to know is every week, make a mini sample, taking 2 tea spoons from your bourbon barrels , and 17 from your left over 5 gallons (I assume of your 5 gallon batch, 2 liters went into the mini bourbon barrels, leaving 17 liters).

19 teaspoons = 3.17 ounces, enough for you to decide if you like the flavor.

kingwood-kid said:

I will freely grant the possibility that I am totally mistaken, but I'm guessing that the flavors you get from extended aging are different (i.e., not just more intense) than the flavors you get from short-term contact. Were they not, I would think bourbon manufacturers would use tiny barrels for a year instead of enormous ones for 18 years. I think the total time you would want to age would still be 6 months or whatever, and that the extra flavors during this time would then be spread throughout the 5 gallons of beer. Aging time is also greatly impacted by temparature and temp fluctuations, more fluctuation speeding things along.

The surface area of the barrels is easy math. The top and bottom are each Pi multiplied by the radius squared. The side of the barrel would be Pi x diameter x height, except that the barrel bows out in the middle, so sub 4 for Pi as a back-of-the-envelope type calculation. Of course, you don't have a 53 gallon barrel to measure.

Click to expand...

There is a deeper flavor from longer aging, partially due to slight oxidation (particularly for liquor) and mellowing from tannins smoothing out with time. However, many of the craft distillers do use smaller barrels because they can turn out more product quickly but don't yet have the production volume or demand to fill 55-60 gallon barrels. That's why you're seeing those 5-10 gallon barrels coming out to homebrewers.

The problem with aging beer too long in those smaller barrels is that the barrel flavor can overwhelm the beer very quickly. If you've ever had a beer that has been over-oaked, it's not half as pleasant as you think. Even with used whisky barrels.

ReverseApacheMaster said:

The problem with aging beer too long in those smaller barrels is that the barrel flavor can overwhelm the beer very quickly. If you've ever had a beer that has been over-oaked, it's not half as pleasant as you think. Even with used whisky barrels.

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As I read it, the OP is only planning on aging 2L, or about 10% of the total batch. If you can age the entire batch for a year in a big barrel, I wouldn't think you could really go overboard aging 10%, no matter how long it sat. Getting the blend right in the end would still be important, of course.