May wine –
done right!

Shimadzu LC Product Manager, Dr. Gesa Schad, recently recalled how the use of woodruff in May wine is a popular spring tradition in Germany. When she first started looking for May wine recipes, she was aware that woodruff contains the natural flavoring coumarin, which can be harmful to health in high doses. But when she was researching recipes, she realized: There are huge differences in the recommended “extraction time”, meaning how long the dried woodruff can be left in the wine without running the risk of reaching the permitted limits for coumarin. On one site, the maximum permissible “infusion time” was 45 minutes, while another stated that the plant should be left to infuse in the wine “for 1–3 hours, depending on the desired flavor intensity”.[1–4] So what should you do if you want to make a wine that has a nice woodruff flavor but without a dangerous coumarin content? Dr. Schad’s curiosity as a researcher was sparked! In order to be able to make a scientifically sound recommendation, it was first necessary to analyze the coumarin content in woodruff extracts with various extraction times. Her colleague at the time, Robert Ludwig, carried out the test series. The results of his quantitative determination are analyzed in more detail in this article in light of the established limits for coumarin in foodstuffs. The results are explained at the end, along with the recommendation on how to safely prepare May wine.

Table 1 gives an overview of the maximum levels of coumarin permitted by law in certain compound foods where flavorings and/or food ingredients with flavoring properties have been added (coumarin is permitted in these food ingredients and in flavorings, whereas coumarin as such may not be added to foods).[5]

There is no defined limit value for beverages, however, the tolerable daily intake (TDI) value can be taken into account to assess the results described below [6], where a daily intake of 0.1 mg coumarin per kilogram of body weight is considered harmless.

Gesa Schad harvested woodruff from a commercially available plant and dried the parts of the plant overnight. Once dried, she tied together 3 g of the cut stems with a string and hung them upside down in 90 ml of white wine for extraction (a ratio of woodruff to wine commonly used for extraction in recipes), without immersing the cut ends in the liquid. Samples were taken at different times, which were filtered only through a 0.45-μm filter before injection into the HPLC (High Performance Liquid Chromatography). Robert Ludwig carried out the HPLC method on a Nexera XS system with binary pumps and a PDA detector.

The analytical conditions are listed in Table 2.[7]