Key takeaways
- Hot water extraction is the modern version of the traditional mushroom decoction.
- It mainly draws out polysaccharides, including beta-glucans, and other water-soluble compounds.
- Temperature, time, particle size and water ratio all affect the result.
- It is poor at extracting triterpenes and sterols, which is why alcohol is often added.
- On its own a water extract spoils quickly; alcohol keeps a tincture stable.
Long before tinctures and capsules, people prepared tough mushrooms such as Reishi and chaga by simmering them in water. Hot water extraction is still the foundation of most mushroom extracts today. This article explains how it works, what it draws out, the variables that matter, how it is done at scale, and where it falls short.
A traditional method
Modern hot water extraction follows the same principle, with more control over temperature, time and the amount of water used.
Decoction or infusion?
There is a useful distinction here. An infusion is made by pouring hot water over material and letting it steep, as with a cup of tea. A decoction is made by actively simmering material in water for an extended period. Delicate leaves and flowers suit infusion; tough, woody materials such as mushrooms, roots and bark need decoction to give up their contents.
What hot water draws out
Water is a very polar solvent, so it dissolves polar compounds well. From mushrooms, that particularly means:
- Polysaccharides, including beta-glucans, released from the cell wall. See What Are Beta-Glucans?
- Proteins and protein-bound polysaccharides.
- Smaller water-soluble compounds, such as nucleosides like cordycepin, ergothioneine and minerals, and, in chaga, oxalates.
Heat is important because it helps loosen the tough, chitin-rich cell wall. Cold water extracts far less.
The variables that matter
- Temperature. Higher temperatures generally release more polysaccharides, but prolonged harsh heating can change some compounds. See Why Extraction Temperature Matters.
- Time. Extraction slows over time, and very long boiling brings diminishing returns.
- Particle size. Sliced or ground material exposes more surface area. For dense species, this can matter as much as time or temperature.
- Water ratio. Enough water to dissolve what’s released and keep the material moving, without over-diluting the extract.
- Repeated extraction. Extracting the same material two or three times with fresh water often draws out more in total than one very long extraction, because each batch of fresh water starts with nothing dissolved in it.
- Agitation. Stirring or circulating the liquid keeps fresh solvent in contact with the material.
Helping the process along
Some producers use additional techniques to break open cell walls during hot water extraction. We use ultrasonic extraction, in which high-frequency sound waves create tiny collapsing bubbles that help disrupt the cells. See Ultrasonic Extraction for Mushrooms.
At industrial scale, some producers also extract under pressure, which allows water to be heated above 100°C.
What hot water misses
Hot water is poor at dissolving less polar compounds such as triterpenes, sterols and hericenones. For a mushroom like Reishi, whose triterpenes are among its best-known compounds, a water-only extract captures only part of the picture. That’s the main reason producers add an alcohol stage. See Alcohol Mushroom Extraction Explained.
After the hot water stage
The liquid is filtered to remove spent mushroom material, and the spent material is often pressed to recover the liquid it holds. See Filtration. Then the extract may be:
- combined with an alcohol extract to make a tincture;
- concentrated by gently evaporating some of the water, sometimes under vacuum, which lets water evaporate at a lower temperature and reduces heat stress on the extract;
- dried into an extract powder, usually by spray drying.
Can I make a mushroom decoction at home?
Many people make chaga or Reishi tea at home by simmering small pieces in water, often for an hour or more. It is a traditional preparation, and it will be a water extract only, so it will contain relatively few of the alcohol-soluble compounds, and it should be kept in the fridge and used within a day or two. If you take chaga this way, bear in mind that hot water also draws out its oxalates. See Chaga Research.
How we use hot water extraction
Our hot water stage uses ultrasonic extraction to help release the contents of UK-grown fruiting bodies and wild Finnish chaga. The extract is then combined with a separate ethanol extract to make our dual extract tinctures, prepared in small batches in Dorset.
