Key takeaways
- Chaga (Inonotus obliquus) grows on birch as a hard, black, cracked mass.
- What’s harvested is a sterile conk, not a typical fruiting body.
- It is almost always wild-harvested, so responsible sourcing matters.
- Chaga is naturally high in oxalates; check with a professional if you have kidney concerns.
- Research is mainly laboratory and animal work; human evidence is very limited.
Chaga doesn’t look like a mushroom at all. On the trunk of a birch tree it appears as a hard, black, deeply cracked mass, a little like burnt charcoal, with a rusty golden-brown interior. It has been brewed as a tea in northern Europe and Siberia for generations. This guide explains what chaga is, how to recognise it, its relationship with birch, how it is harvested responsibly, what it contains, what the research does and doesn’t show, and what to look for in a chaga product.
At a glance
- Scientific name: Inonotus obliquus
- Other names: clinker polypore, birch canker polypore, cinder conk
- Grows on: mainly birch, in cold northern forests
- Part used: the sterile mass (conk) that grows on the tree
- Source: almost always wild-harvested
Not quite a mushroom
What people harvest as chaga isn’t a fruiting body. It is a sterile mass of fungal tissue, sometimes called a sclerotium or conk, that grows out of the tree over many years. The fungus does eventually produce a thin fruiting layer, but usually only after the tree has died, and it is rarely seen. Read Why Chaga Is Not Technically a Mushroom.
How to recognise it
Chaga forms an irregular, black, deeply fissured growth on the trunk of a living birch, typically where the bark was once damaged. Broken open, it shows a hard, cork-like, rusty or golden-brown interior. The black outer crust and the coloured inside together are the clearest signs.
Burls, old wounds and patches of burnt bark can look similar at a glance, but they are wood, not fungus, and lack chaga’s rusty interior. Identification should always be certain, and in any case chaga should only be harvested with permission and with care.
Chaga and birch
Chaga grows mainly on birch trees in the cold forests of Russia, Scandinavia, Finland, Canada and the northern United States, and occasionally in Scotland. It enters the tree through a wound and grows slowly inside the wood, decaying it over many years. The black outer surface is rich in melanin, the same family of pigments found in skin and hair. Some of chaga’s compounds, such as betulin, originate in the birch itself. Read Chaga and Birch Trees.
History
See Chaga in Northern European and Siberian Traditions.
Chaga as a tea
The traditional way to prepare chaga is simple: small chunks are simmered gently in water for a long time, producing a dark, earthy, mildly bitter brew. The same pieces are often simmered more than once. It’s a good illustration of hot water extraction, the method that draws out chaga’s water-soluble compounds. See How Chaga Is Extracted.
Wild harvesting and sustainability
Chaga isn’t easy to cultivate in its familiar form, so almost all chaga is wild-harvested. It grows slowly, and responsible harvesting leaves part of the growth on the tree and avoids over-collecting. Good suppliers should be able to tell you where and how their chaga was harvested. See Chaga Harvesting and Sustainability.
Chaga mycelium can be grown in the laboratory, and some products use it, but that is a different material from the conk that has traditionally been harvested.
What’s inside chaga?
- Melanin, responsible for its dark colour.
- Triterpenes and related compounds, some derived from birch, such as betulin and betulinic acid.
- Polysaccharides, including beta-glucans.
- Oxalates, present in relatively high amounts.
Because chaga contains both water-soluble polysaccharides and alcohol-soluble triterpenes, it is a strong candidate for dual extraction. Read Chaga Compounds Explained.
A note on safety
Chaga is naturally high in oxalates. If you have kidney problems or a history of kidney stones, are taking medication or have any medical condition, speak to a healthcare professional before using chaga. As with any food supplement, don’t exceed the amount stated on the label.
What does the research say?
Common myths
- “Chaga is a mushroom like any other.” What is harvested is a sterile mass, not a fruiting body.
- “Chaga from any tree is the same.” Traditionally, chaga is harvested from birch, and part of its chemistry comes from the tree.
- “More is better.” Chaga’s oxalate content is a good reason to follow the label.
- “There’s endless wild chaga.” It grows slowly, and careless harvesting can deplete it locally.
How to choose a chaga product
- Look for Inonotus obliquus on the label.
- Ask where the chaga was harvested and how.
- Check whether it is the wild conk or laboratory-grown mycelium.
- Check the extraction method: traditional preparation uses hot water.
- Look for testing where available, since wild material can vary.
See How to Choose a Chaga Extract.
Questions people ask
What does chaga taste like?
Earthy, woody and mildly bitter, and less bitter than Reishi. As a tea it is dark and smooth.
Does harvesting chaga harm the tree?
Chaga is itself a parasite that slowly decays the birch it grows on. Responsible harvesters remove only part of the growth, so it can continue to develop, and avoid over-collecting in one area.
Can chaga be cultivated?
Its mycelium can be grown in the laboratory, but the black conk that is traditionally harvested forms slowly on living birch and isn’t practical to cultivate. That’s why almost all chaga is wild.
Why does your chaga come from Finland?
Chaga thrives in the cold birch forests of the far north, and Finland has a long tradition of harvesting it. We source wild chaga harvested from birch there.
Is chaga safe?
Because of its oxalates, people with kidney problems or a history of kidney stones should speak to a healthcare professional first, as should anyone pregnant, breastfeeding, taking medication or with a medical condition. Follow the label.
How we make our chaga tincture
Our Chaga tincture is made from wild chaga harvested from birch in Finland. We extract the dried chaga in hot water using ultrasonic extraction and in plant-derived ethanol, then combine the two in small batches in Dorset, with nothing else added.