In my days as archivist at United Distillers I was able to access many interesting pieces from the old Schenley collection in the archives. One of these items was copy from The Journal of the American Chemical Society from January 1908 on whiskey stored in wood. The article was written by C.A. Crampton and L.M. Tolman written in 1907 for the Bureau of the Commissioner of the Internal Revenue. This is an interesting article for anyone interested in aging whiskey. It is not light reading and a knowledge of chemistry is necessary for full understanding of the results. I am not a chemist but I still found many of the points very interesting.

The study began with 9 samples from each of 31 packages of the same age with the difference between the samples being the time in the barrel.

  • Sample one was new whiskey stored in glass for 8 years.
  • Sample two was aged one year in wood and seven years in glass.
  • Sample three was stored two years in wood and six years in glass.
  • The other samples were held in wood for in progression of increasing the age in wood and then glass.

They studied the color and the amount and types of solids present in each sample. There are descriptions of each sample giving the variables. Often they note the quality of the flavor and taste of the spirit. This of course is a bit subjective.

They looked at many types of whiskey and noted how they were distilled and where they were stored. Some of the variables include Bourbon, corn and rye whiskeys and whether they were sweet mash or sour mash whiskeys. They listed the yield from the mash. Column and pot stills, as well as, a wooden still. They looked at iron clad and brick warehouses and whether they were steam heated or not. They listed the average temperature of both the summer and winter while aging. Two of the samples were stored in uncharred barrels. Some of the samples were “rectified” by increasing the distillation proof or filtered through charcoal. One whiskey was treated with a charcoal mellowing vat and one rye contained molasses.

The results are listed on tables showing different chemical effects. This is where I wish I had a greater knowledge of chemistry so I could fully understand what the tables are meant to show. I still find the article very interesting. Unfortunately, they state that the data showing the change in volume as it was stored was not available for the study, but they did do an estimate based upon the data they had. They still had plenty of interesting information to look at. They show that the solid material increases with time in the barrel. The loss of volume was not due only to evaporation as they determined some of the loss was due to the spirits passing through the pores of the wood. They determined that water passed through the wood faster than the alcohol. Spirits that were “highly rectified” and higher proof were not as flavorful as the samples at lower proof. Clearly a subjective conclusion.

The conclusions reached in the article are things we now consider as common knowledge:

  • First of all, whiskey matures by taking on flavor compounds from the wood.
  • Whiskey does not continue to mature in glass.
  • Charred wood gives a different flavor than uncharred wood.
  • Acids and esters reach an equilibrium after three or four years and the improvement of the flavor after four years is due to concentration.

The conclusion I found most interesting was “The rye whiskeys show a higher content of solids, acids, esters, etc., than do Bourbon whiskeys, but this is explained by the fact that heated warehouses are almost universally used for the maturing of rye whiskeys, and unheated warehouses for the maturing of Bourbon whiskeys.” They concluded that heated warehouses make a significant difference in the maturation of whiskey.

The article still has merit in the modern world of whiskey. A distiller would find it well worth looking at and I would hope to see someone do a similar study again.

Photos Courtesy of Maggie Kimberl