Issue Date: July 28, 2008
The letter from Mike Stapleton needs rebuttal, as it contains a number of factual errors (C&EN, June 16, page 9). The first and foremost misrepresentation is the boiling point of thujone, which the letter states to be 84 °C. In fact, this is obviously a boiling point measured at reduced pressure (most likely the "bp17" according to the "Merck Index"). A current search in SciFinder shows that the boiling point of thujone (CAS No. 546-80-5) at 760 Torr is 199–201 °C. This invalidates the argument that the terpene is "fairly volatile" at atmospheric pressure storage conditions such as in the case of our vintage absinthes.
The other claims that "absinthe cannot go unchanged during many years of storage" and "this beverage is particularly susceptible to chemical and physical changes" also completely lack scientific or evidential foundation. We can only speculate that there was confusion with the storage properties of wine or beer. In our view, the practical assumption would be that absinthe, like other high-proof spirits (for example, cognac) tightly sealed in anaerobic glass bottles, does not change significantly with time.
We accept that there are few research papers on the stability of thujone in alcoholic solutions; however, the existing research consistently indicates that thujone is stable under normal storage conditions and seems to be affected only by high doses of UV irradiation (J. Agric. Food Chem. 2008, 56, 3073). Our own experiments showed that even under accelerated aging conditions, the thujone content was not affected in absinthe manufactured according to historical principles. We explained this stability by, among other things, the action of natural antioxidants extracted from the herbs during the coloring of absinthe (Forensic Sci. Int. 2006, 158, 1).
A further indicator that thujone does not deteriorate significantly over time is the fact that modern absinthes made scrupulously according to Belle époque recipes generally have thujone levels in the same range as the preban absinthes we tested. As the question about stability of thujone appears to be the final argument in the discussion about vintage preban absinthe, we are currently reinvestigating the long-term stability of the beverage and will hopefully provide the "once-and-for-all evidence" in the near future.
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