Sweet Woodruff: The Hay-Scented Herb of German May Wine, and Its Coumarin

Fresh sweet woodruff smells of very little. Dried, it smells of hay and vanilla with an almond-like sweetness, and that’s the herb behind German May wine. It’s Galium odoratum, a small temperate perennial, and it contains coumarin, a compound that’s released as the cut plant dries and that regulators limit in food. The good news for May wine: a 2024 study concluded that if you keep steeping under 5 hours and share the batch, no harmful effects of coumarin are to be expected.¹

At a glance

What sweet woodruff is

Galium odoratum is a small perennial of the temperate biome, up to 30 cm tall. The French Pharmacopoeia’s monograph uses the fresh, flowering aerial part of the plant and lists Asperula odorata as its older name.

Where it comes from

Kew gives the native range as temperate Eurasia and Algeria, from Spain, France and Great Britain across Europe and Russia to Iran, China, Korea and Japan. It lists the plant as introduced in Colorado, Illinois, Minnesota, New York and Vermont.⁴ The Wolters Kluwer monograph on Drugs.com says it’s native to Eurasia and North Africa and grows throughout North America, a broader claim than Kew’s list supports.⁵

Flavor and aroma

The French Pharmacopoeia describes the smell as that of harvested hay. The dried herb smells of hay and vanilla with an almond-like sweetness, while the fresh leaves smell of very little. Steep it too long and it turns bitter, so keep infusions short.

Coumarin

Coumarin is the compound regulators track in sweet woodruff. One food-chemistry paper describes it as well known for its pleasant vanilla-like smell. ANSES, the French food safety agency, says that in the aerial parts of sweet woodruff, coumarin’s precursor is mostly found as a glucoside.² The Drugs.com monograph says the coumarin is freed by enzyme action during drying.⁵ Plenty of May wine recipes call for wilted or dried woodruff.

How much coumarin the plant contains isn’t settled. The figures below come from different samples and methods, so don’t average them:

The monograph also lists asperuloside at 0.05% among minor components.⁵

How sweet woodruff is used

• May wine. Steeping woodruff in wine is, in the words of one 2024 lab study, a popular spring tradition in Germany.¹ The Drugs.com monograph describes May wine as woodruff soaked in sweet white wine, and adds that woodruff flavors vermouth and some bitters.
• Perfumery. The monograph notes that the extract goes into perfumes and other fragrances.

We couldn’t trace claims that woodruff flavors sorbets, ice cream and fruit salads, Cheshire cheese, German sherbet powder or Scandinavian cordials.

How much coumarin ends up in May wine

The 2024 study by Bollig and Schad hung bundles of dried woodruff in white wine, at a ratio the authors describe as common in recipes, and measured coumarin over time. The concentration kept rising through the whole 20-hour experiment, and only after 20 hours of steeping did a glass of the finished drink reach 6.9 mg. The authors concluded that if you keep steeping under 5 hours, and share the batch instead of drinking it all yourself, no harmful effects of coumarin are to be expected.¹

The Drugs.com monograph cites a suggested safety limit of under 5 ppm coumarin in spiced wine, which it equates to about 3 to 3.5 g of fresh woodruff per liter.⁵ That’s the monograph’s figure, not a regulation.

Buying and storage

We found no grading standard and no published shelf-life figure for the dried herb.

Safety and regulation

Coumarin limits

• EU. EFSA keeps a tolerable daily intake of 0.1 mg coumarin per kg of body weight.⁶ EU flavoring rules set maximum coumarin levels in certain foods that contain flavorings or flavoring ingredients, including 5 mg/kg in desserts and 20 mg/kg in breakfast cereals.⁷ The 2024 May wine study notes that there’s no defined limit for beverages.¹
• US. Coumarin added to food is treated as adulteration under 21 CFR 189.130.⁸ Sweet woodruff itself appears on FDA’s list of natural flavoring substances with the restriction “in alcoholic beverages only.”³ The Drugs.com monograph’s statement that the plant is generally recognized as safe as a food flavoring doesn’t match that listing.⁵³

Health effects

The main worry with coumarin is the liver. The Drugs.com monograph says hepatotoxicity may occur with long-term exposure, reports clotting anomalies and liver damage in animal studies, and advises avoiding woodruff during pregnancy and breastfeeding. It also says excessive doses may cause internal bleeding.⁵ ANSES disagrees on that point for coumarin itself. It states that simple coumarins don’t have anticoagulant properties, which belong to dimeric derivatives such as dicoumarol.² No source we opened supports the often-repeated claim that sweet woodruff is a blood thinner or is grown as a source of a coumarin drug.

The monograph reports anti-inflammatory activity from woodruff extract in rats, but says research reveals no clinical data on woodruff for any condition.⁵ We couldn’t trace claims that it improves circulation, calms anxiety, treats insomnia or arthritis, or relieves constipation through anthraquinones. We make no claim that sweet woodruff treats or prevents any condition.

Substitutes and comparisons

For the vanilla-and-hay note, a little vanilla is the closest stand-in in desserts and drinks. Related pages:

• Vanilla and too much vanilla
• Mahlab, another coumarin-scented flavoring
• Cassia cinnamon, another source of coumarin
• German spices
• Lemon verbena and lavender, other herbs for flavoring drinks and desserts