In the highlands of Northern Thailand, a traditional fermented tea known as Miang has been produced for centuries, its survival depending on mysterious microbes that thrive in a toxic environment. For the first time, scientists are uncovering these microbial secrets, revealing potential solutions for both gut health and sustainable food production.
For generations in the mountainous regions of Northern Thailand, from Chiang Mai to Nan and Phrae provinces, forest dwellers have practiced the art of Miang production—a traditional fermented tea made from the leaves of Camellia sinensis var. assamica 2 . Unlike typical brewed teas, Miang is unique in that it is eaten or chewed rather than drunk, frequently consumed after meals and served at ceremonial occasions throughout northern Thailand 2 .
Astringent Miang with a shorter fermentation period of 7-28 days
Sour Miang which undergoes extended fermentation for 3-12 months
What makes this fermentation process particularly remarkable is the challenging environment these microorganisms must overcome. Tea leaves contain significant amounts of tannins—polyphenolic compounds considered potent inhibitors of many microorganisms 2 . The bacteria that survive and thrive in this tannin-rich environment represent a specialized class of microbial specialists with unique abilities that science is just beginning to understand.
The production method is remarkably simple yet effective: young, soft tea leaves are harvested, bundled, steamed, and then tightly packed into containers or bamboo baskets to create anaerobic conditions perfect for lactate fermentation 7 .
Young, soft tea leaves are carefully selected and harvested
Leaves are steamed to prepare them for fermentation
Steamed leaves are tightly packed into containers or bamboo baskets
Anaerobic conditions allow lactate fermentation to transform the leaves
Initial fermentation begins, microbial communities establish
Miang-Faat develops - astringent variety with shorter fermentation
Extended fermentation phase, flavor profile deepens
Miang-Som matures - sour variety with complex microbial ecosystem
Through meticulous scientific investigation, researchers have identified the microorganisms responsible for Miang fermentation. The primary actors belong to the Lactobacillus genera, with an overwhelming predominance of what scientists call the Lb. plantarum group 1 5 .
In a comprehensive study published in the Journal of Microbiology in 2017, researchers isolated 311 presumptive lactic acid bacteria strains from 35 Miang samples collected across 22 different regions of eight provinces in upper northern Thailand 1 .
Through advanced genetic analysis including repetitive genomic element-PCR fingerprinting profiles, they made a fascinating discovery: while 201 of the 252 isolates in the Lb. plantarum group were indeed Lb. plantarum, the other 51 belonged to Lb. pentosus 1 5 .
The revelation of Lb. pentosus as a significant component of Miang's microbiota was particularly intriguing to scientists. As researcher Chaikaew and colleagues noted, "In contrast to Lb. plantarum, there is a lack of information on the tannase gene and the tea tannin-tolerant ability of Lb. pentosus" 1 5 .
This knowledge gap set the stage for a deeper investigation into the extraordinary capabilities of these bacterial strains.
To understand the remarkable adaptability of these bacteria, researchers designed a crucial experiment to test their tannin-tolerant capabilities. The question was simple yet profound: How do these bacteria survive in such a tannin-rich environment?
First, scientists screened the 51 Lb. pentosus isolates for the presence of genes encoding tannase—the enzyme responsible for breaking down tannins 1 .
They discovered that 33 of the 51 isolates harbored these tannase genes, which shared 93-99% amino acid identity with tannase obtained from Lb. pentosus ATCC 8041T 1 5 .
Next, these 33 tannase gene-positive isolates were cultivated on de Man Rogosa and Sharpe agar-containing bromocresol purple (MRS-BCP) supplemented with 20% (v/v) crude tea extract, corresponding to 2.5% (w/v) tannins 1 .
This high-tannin environment would be toxic to most microorganisms.
| Reagent/Material | Function in Research | Specific Example |
|---|---|---|
| MRS-BCP Agar | Growth medium for lactic acid bacteria containing pH indicator | de Man Rogosa and Sharpe agar with bromocresol purple 1 |
| Crude Tea Extract | Provides natural tannins for tolerance testing | 20% (v/v) extract corresponding to 2.5% (w/v) tannins 1 |
| rep-PCR | Genetic fingerprinting for strain identification | Repetitive genomic element-PCR for clustering analysis 1 |
| Species-Specific PCR | Precise species identification within LAB groups | Differentiation between Lb. plantarum and Lb. pentosus 1 |
| Tannase Gene Probes | Detection of tannin-degrading genetic elements | Identification of genes encoding tannase enzyme 1 |
The discovery of these tannin-tolerant bacteria extends far beyond the traditional production of Miang. Modern science is now exploring how these specialized microbes might contribute to human health, particularly gut barrier integrity and overall digestive wellness.
Recent research has revealed fascinating synergies between lactic acid bacteria and tannins. A 2024 study demonstrated that Lactobacillus rhamnosus GG and tannic acid synergistically promote gut barrier integrity in experimental models of diarrhea 3 .
The combination maintained intestinal mucosal structure and proliferative activity while preserving the expression of zonula occludens-1 (ZO-1), a critical tight junction protein 3 .
The therapeutic potential appears to work through selective immunomodulatory mechanisms. While LGG treatment remarkably decreased intestinal tissue concentrations of tumor necrosis factor-alpha and nuclear factor Kappa beta, tannic acid treatment led to a selective decrease of interferon-gamma and transforming growth factor-beta 3 .
This complementary action suggests why the combination showed the most significant effect.
Furthermore, fermented tea products like Miang contain high levels of flavanols, commonly known as catechins, which act as effective antioxidants 4 . These compounds protect against various illnesses, including inflammation, diabetes, hypertension, cancer, and obesity 4 . The interaction between tannin-tolerant lactic acid bacteria and these bioactive compounds creates a potent combination with significant health implications.
The 23 identified Lb. pentosus isolates with high tannin-tolerant capacity represent more than just successful fermenters—they are potential probiotics with specialized adaptations 1 7 . As research continues, these strains may find applications in:
Designed for enhanced bioavailability of plant-based nutrients
For gastrointestinal disorders
As natural preservatives or processing aids
Methods that utilize tannin-rich plant materials
As one recent study confirmed, "Miang contains lactic acid bacteria that could potentially be used as probiotics" 7 , with many isolates exhibiting tolerance to simulated gastric juice at pH 3 and simulated intestinal juice at pH 8—essential characteristics for effective probiotics 7 .
The ancient tradition of Miang production, once a localized cultural practice, now offers insights that bridge traditional knowledge with modern science. As researchers continue to unravel the secrets of these tannin-tolerant bacteria, we gain not only appreciation for microbial adaptation but also promising tools for addressing contemporary health challenges through nature's own designs.