‘Puer’ (or pu’er, pu’erh, or 普洱 – pronounced pooh like the bear, and arhh like a pirate)… means multiple things. Firstly, it’s a place in China. As most places in China, Puer regional history is recounted with millennia rather than centuries. It’s a Southwest border region, meaning that Puer harbors the dense tropical mountains, dividing China from Laos and Vietnam.

Tropical Mountains of Puer

In fact, these altitudinous tropics, not far from where the Indian subcontinent mashes abruptly into the tectonic plates of Eurasia, is the evolutionary birthplace of tea (Camellia sinensis). Thus, Puer to C. sinensis resembles our ancestral relationship with East Africa. A rainforest frontier, an evolutionary birthplace, and a historic cradle of East Asian civilization… Puer is a place… with tea.

Puer tea is not just tea leaves from Puer. Puer is a tea production style… but more so a hairstyle (kidding). No, Puer tea has TWO types – raw and ripe. Raw Puer is like green tea but made so that it ages like fine wine, smoothing out and mellowing over time. Ripe Puer is made so that the aging process is accelerated by pile heaping the tea leaves, adding water, and inoculating microbes into the heap, much like cheese, bread, or ice cold Coors Light cold as the rocky mountains (beer sponsor of Wu Mountain Tea).

Post-Fermented Puer Tea leaves

The smoothing and mellowing of flavor that takes a decade+ with raw Puer happens over the course of 6 weeks during Ripe Puer processing. Microbes do not waste time.

Here’s a couple of microbially-mediated changes that occur during Puer ripening:

  • Caffeine concentration in tea leaves increases due to microbial metabolism of caffeine precursors into caffeine – generally by about 20% (Wang et al., 2018).
  • A compound related to caffeine, known as theophylline, also increases significantly during Puer ripening due to microbial metabolism (Wang et al., 2018; Zhou et al., 2020a; Zhou et al., 2019; Zhou et al., 2018; Zhou et al., 2020b). Theophylline is neat – it’s a psychoactive compound similar (structurally) to caffeine, but instead of creating a stimulating buzz it’s more calming and anxiolytic, which synergizes with caffeine to induce a relaxed and productive mind state.
  • The profile of antioxidant polyphenols changes dramatically during pile fermentation (Puer ripening). In short, catechins (or tannins), which comprise a huge fraction of total dry weight in raw tea leaves, either mash into each other (via enzymatic oxidation) to form theabrownins, or are digested, degraded and splintered off into little fragments including gallic acid and other polyphenol metabolites (Zhao et al., 2019). Overall, the antioxidant capacity declines compared to other tea types (Kosińska and Andlauer, 2014), but that is NO BIG DEAL. Puer tea retains some antioxidant capacity, and besides, it’s not always great to bombard your body with antioxidants. Moreover, theabrownin and gallic acid impart their own suite of health benefits, including the regulation of blood cholesterol by theabrownins (Gong et al., 2010; Huang et al., 2019) and weight-loss/anti-obesity effects of gallic acid through the inhibition of pancreatic lipase (Lee and Foo, 2013; Oi et al., 2012).
  • In terms of flavor, Puer ripening increases the contents of water-soluble pectin (sort of a sticky plant glue/gelatin) and tea polysaccharides, which forms the celebrated silky-smooth mouthfeel and undeniable sweetness of Ripe Puer (Kim et al., 2012). The saccharides in Puer Tea don’t spike blood sugar, but actually Puer tea lowers blood glucose due to the abundance of alkaloids (i.e. caffeine and related compounds) (Fang et al., 2015)).
Ripe Puer is rich, thick, and dark.

While volumes have been written about Ripe Puer, this post merely offers a brief overview of Puer Tea, and characterizes a few of the critical microbially-mediated alterations that underlie Puer Ripening.

More to come on this topic, but for now, this.

Thanks for reading,


  • Fang, C.Y., Wang, X.J., Huang, Y.W., Hao, S.M., Sheng, J., 2015. Caffeine is responsible for the bloodglucose-lowering effects of green tea and Puer tea extractsin BALB/c mice. Chin J Nat Med 13, 595-601.
  • Gong, J., Peng, C., Chen, T., Gao, B., Zhou, H., 2010. Effects of theabrownin from pu-erh tea on the metabolism of serum lipids in rats: mechanism of action. J Food Sci 75, H182-189.
  • Huang, F., Zheng, X., Ma, X., Jiang, R., Zhou, W., Zhou, S., Zhang, Y., Lei, S., Wang, S., Kuang, J., Han, X., Wei, M., You, Y., Li, M., Li, Y., Liang, D., Liu, J., Chen, T., Yan, C., Wei, R., Rajani, C., Shen, C., Xie, G., Bian, Z., Li, H., Zhao, A., Jia, W., 2019. Theabrownin from Pu-erh tea attenuates hypercholesterolemia via modulation of gut microbiota and bile acid metabolism. Nature Communications 10, 4971.
  • Kim, M.-J., Kim, S.-S., Lee, S.-I., 2012. Quality Characteristics and Content of Polysaccharides in Green Tea Fermented by Monascus pilosus. Preventive nutrition and food science 17, 293-298.
  • Kosińska, A., Andlauer, W., 2014. Chapter 12 – Antioxidant Capacity of Tea: Effect of Processing and Storage, in: Preedy, V. (Ed.), Processing and Impact on Antioxidants in Beverages. Academic Press, San Diego, pp. 109-120.
  • Lee, L.K., Foo, K.Y., 2013. Recent advances on the beneficial use and health implications of Pu-Erh tea. Food Research International 53, 619-628.
  • Oi, Y., Hou, I.C., Fujita, H., Yazawa, K., 2012. Antiobesity effects of Chinese black tea (Pu-erh tea) extract and gallic acid. Phytother Res 26, 475-481.
  • Wang, Y., Kan, Z., Thompson, H.J., Ling, T., Ho, C.-T., Li, D., Wan, X., 2018. Impact of Six Typical Processing Methods on the Chemical Composition of Tea Leaves Using a Single Camellia sinensis Cultivar, Longjing 43. J Agr Food Chem.
  • Zhao, M., Su, X.Q., Nian, B., Chen, L.J., Zhang, D.L., Duan, S.M., Wang, L.Y., Shi, X.Y., Jiang, B., Jiang, W.W., Lv, C.Y., Wang, D.P., Shi, Y., Xiao, Y., Wu, J.-L., Pan, Y.H., Ma, Y., 2019. Integrated Meta-omics Approaches To Understand the Microbiome of Spontaneous Fermentation of Traditional Chinese Pu-erh Tea. Msystems 4, e00680-00619.
  • Zhou, B., Ma, C., Ren, X., Xia, T., Li, X., 2020a. LC–MS/MS-based metabolomic analysis of caffeine-degrading fungus Aspergillus sydowii during tea fermentation. Journal of Food Science 85, 477-485.
  • Zhou, B., Ma, C., Ren, X., Xia, T., Li, X., Wu, Y., 2019. Production of theophylline via aerobic fermentation of pu-erh tea using tea-derived fungi. BMC Microbiology 19, 261.
  • Zhou, B., Ma, C., Wang, H., Xia, T., 2018. Biodegradation of caffeine by whole cells of tea-derived fungi Aspergillus sydowii, Aspergillus niger and optimization for caffeine degradation. BMC Microbiology 18, 53.
  • Zhou, B.X., Ma, C.Q., Xia, T., Li, X.H., Zheng, C.Q., Wu, T.T., Liu, X.H., 2020b. Isolation, characterization and application of theophylline-degrading Aspergillus fungi. Microbial Cell Factories 19.