Evaporation of Bourbon from a Wooden Barrel

[potus77]

How would i go about calculating the loss of Bourbon 120 proof 60% ALC/VOL and/or Water from a wooden barrel stored in a warehouse, knowing the ambient temp, RH% and Dew Point, Know as the angels share. per period of time?

 

[Bobbywhy]

Is the wooden storage barrel sealed? Completely closed? If yes, then none lost to the Angels. But, if the wood has some permeability, which would allow alcohol to pass through, then yes, you would lose some. How to calculate that amount? Sorry, but I've no idea how.

 

[Andy Resnick]

Flow through the wall of a permeable cylindrical object can be modeled as:

$$v_{R}=\frac{K}{\mu} \frac{\Delta p}{d}$$

Where v is the velocity of the radial flow (i.e. out of the container), K the permeability, μ the viscosity of the fluid, and Δp/d the pressure gradient between inside and outside. Using the vapor pressure of EtOH (6 kPa), a wall thickness of 2 cm, and a permeability of wood of 0.1 milliDarcy (a crude estimate based on http://eng.med.wanfangdata.com.cn/PaperDetail.aspx?qkid=zwxb&qcode=zwxb200102002 and http://en.wikipedia.org/wiki/Darcy). Then, convert v to a volume flow Q = v* area of barrel- I estimated 0.3 liters/hr, which is *way* too high.

Alternatively, you can use the measured losses as a measurement of K. A barrel holds about 180 liters and is aged for (say) 7 years- a 30% loss is 9*10^-4 liters/hr, so the permeability is likely closer to 0.1 microDarcy.

 

[potus77]

Thanks,

how to predict evaporation from white oak bourbon and scotch barrels has been a century old challenge. we put 53 gallons of 124 proof spirits in a oak barrel place it in a warehouse for 4-8 years. when the barrel is emptied 22% of the liquid is gone. there are times when the volume of water is lower and the alcohol is higher, other times the water is higher and the alcohol is lower. This seems to be related to the temperature and RH% in the warehouse. The alcohol or water wicks through the wood of the barrel. I was wondering what was happening. Some say it is Vapor Pressure Deficit between the liquid in the barrel and the ambient temperature and RH% anyone have a guess? how can we measure the temperature, RH% or dew point of the warehouse and predict what will leave the barrels??

 

[Andy Resnick]

The vapor pressure of water at 25C is about 3 kPa, so by measuring the RH with (say) a hygrometer, you can calculate the pressure gradient for water. The permeability for water through the barrel is assuredly different than ethanol, and I'm sure there considerable variation in the permeability from barrel to barrel for both.

I'm curious about water leaving faster than ethanol- that's not what I would expect. Was there something unusual?