Definition
From a technological standpoint, fermentation of the kratom leaf is a controlled oxidation and enzymatic conversion of the plant material between harvest and drying. The aim is primarily to change the ratio of alkaloids and, secondarily, the organoleptic properties of the raw material (colour, smell). In the specialist literature the process is sometimes described as "post-harvest processing", because it is not classical microbial fermentation but a combination of enzymatic and oxidative transformation.
What leaf fermentation is
Unlike acidic lactic or alcoholic fermentation carried out by microorganisms, in the case of kratom fermentation is driven primarily by:
- the plant's own enzymes (polyphenol oxidases, peroxidases),
- atmospheric oxygen (chemical oxidation of alkaloids and polyphenols),
- leaf moisture (which governs the rate of the enzymatic reactions),
- temperature (which accelerates oxidation but destroys the enzymes above 45 °C).
A similar principle is known in tea fermentation (the conversion of green tea into black) - there too it is primarily enzymatic oxidation, not a microbial process.
Stages
1. Harvesting and sorting
The leaves are hand-sorted by vein colour and maturity phase. For the classic "red" product, riper leaves with a higher anthocyanin content are selected.
2. Withering
The leaves are left in a shaded, ventilated space for 6-24 hours so that they lose some water (from the original ~70 % to ~55 % moisture). At this stage the enzymes are activated, but the leaf does not yet begin to oxidise intensively.
3. Fermentation / oxidation proper
The leaves are stored in layers (5-10 cm) in closed bags or containers for 12-72 hours. Enzymatic oxidation of polyphenols and mitragynine takes place, and the leaf changes colour to a darker shade. The temperature is monitored to keep it from exceeding 40 °C.
4. Drying
Final drying takes place in the sun or in a dryer at 35-45 °C until the water content falls below 10 %. This stops the enzymatic reactions and stabilises the final profile. More in the article Storing kratom powder.
Effect on the ratio of alkaloids
The key impact of fermentation on the chemistry of kratom:
- The absolute content of mitragynine falls by 10-30 % (it is oxidised).
- The content of 7-hydroxymitragynine rises, sometimes 2-5× compared with unfermented leaf.
- The proportion of oxindole alkaloids (mitraphylline, isomitraphylline) increases slightly.
- The polyphenolic profile changes - oxidised derivatives are formed (compounds similar to the thearubigins of tea).
This "shift" is the main reason why "red" variants tend to be described as relatively stronger - from a purely chemical standpoint it means a higher proportion of 7-OH-MG in the alkaloid profile.
Variability between producers
The specific parameters of fermentation differ dramatically between producers. Key differences:
- the fermentation time (12 vs. 72 hours),
- the temperature and humidity of the environment,
- the thickness of the leaf layer (which ensures access to oxygen),
- the subsequent drying (sun vs. fan).
For this reason, two "red" raw materials from different producers may have entirely different alkaloid profiles. A reliable figure is provided only by HPLC analysis of a specific batch.
Frequently asked questions
Does fermentation change the toxicity of the raw material?
Not in itself. The fermentation process does not introduce new toxic compounds, but improper conditions (high humidity, long duration) can allow mould growth and the formation of mycotoxins.
Can fermentation be replicated at home?
Technologically yes, but without analytical equipment neither the final alkaloid profile nor the microbiological safety can be verified.
How long does the process take?
Full fermentation takes 12-72 hours, with the subsequent drying a further 12-48 hours. The whole cycle is therefore 1-5 days depending on the climate and the method.
Does fermentation differ between kratom and tea?
The principle (enzymatic oxidation) is similar, but the enzymes and substrates are different. Tea ferments catechins; kratom ferments alkaloids and polyphenols.
References
- Sengnon N. et al. (2021). Phytochemical comparison among different colour-vein cultivars of Mitragyna speciosa. Molecules, 26(17), 5141.
- Brown P. N. et al. (2017). A botanical, phytochemical and ethnomedicinal review of the genus Mitragyna. Journal of Ethnopharmacology, 202, 302-325.
- Singh D. et al. (2016). Traditional and non-traditional uses of Mitragyna speciosa. Journal of Ethnopharmacology, 192, 24-34.
