POSSIBILITIES TO REDUCE THE THUJONE CONTENT
Today’s manufacturers face the problem that they have to generate a distinctive wormwood taste, without exceeding the thujone maximum limit of 35 mg/kg. The selective enrichment of the bitter and flavor compounds, while keeping the thujone concentration low, was extensively investigated (45).
Tegtmeier et al. (46) compared a water extraction to an alcohol extraction method By the percolation with water or alcohol (30%vol) no thujone could be extracted, because the solubility of thujone in water is poor. Only by the application of ethanol 90%vol, it was possible to extract 0.18 mg thujone per g wormwood herb. When the method of digestion with ethanol 30%vol was applied, 0.17 mg thujone per g wormwood herb could be extracted. The largest yields were obtained, whenever the macerate of the wormwood herb was distilled (0.24 mg thujone/g). The use of hot and highly concentrated alcohol for the extraction should therefore be avoided to obtain extracts with a low content of thujone. Because the percolation with pure water might lead to a loss of microbiological quality, the percolation with ethanol 30%vol is regarded as the method of choice. This method is described as being easy to handle and economic. Gambelunghe and Melai (47) verified these results. Wormwood macerated with ethanol 20%vol for 30 days contained only 0.2 mg/I of thujone, while the maceration of wormwood with ethanol 95%vol for 6 months contained 62 mgll of thujone. The consequence for the absinthe manufactures is that traditional recipes and methods have to be modified, in order to avoid thujone contents, which exceed the limit. The maceration should be done with low concentrations of alcohol and the wormwood herb should be separated before the distillation.
A possibility for the continuation of traditional recipes is to remove the thujone from the wormwood herb before the maceration. Stahl and Gerard (48) observed, that the extraction with liquid or supercritical carbon dioxide provides a fast, selective and quantitative method for the separation of thujone from the wormwood herb. Absinthin, which is responsible for the high bitter value of wormwood, remains in the herb. It is therefore possible to generate nearly thujone free wormwood herb and to use it for the manufacturing of absinthe. However, the application of this method for the manufacturing of spirit drinks was never described.
The most elegant alternative to avoid the toxic thujone may be the use of thujone-free wormwood herb, which is available in certain cultivation areas,IO.16 and appears to be perfect for the use in the spirit drink producing industry. With those chemotypes, it would be possible to produce absinthe with wormwood quantities on the basis of the traditional recipes, without the manufacturer facing the risk of exceeding the thujone limit.
Lachenmeier, D. W., S. G. Walch, S. A. Padosch, and L. U. Kroner. 2006. Absinthe–a review. Crit Rev Food Sci Nutr 46:365-77.