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Course:FNH200/Projects/2026/Pu-Erh Tea

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Pu-erh Tea (Endangered Food)[1]

Introduction

Compressed Pu-erh tea cake and brewed Pu-erh tea. Image by OGBerserk, Wikimedia Commons (CC0 1.0 Public Domain).[2]

Pu-erh (pu’er) tea is a traditional Chinese tea produced from the leaves and buds of Camellia sinensis var. assamica, a tea plant variety primarily cultivated in Yunnan Province, China.[3][4] Unlike many other teas, Pu-erh tea undergoes post-fermentation, during which microbial activity after initial processing gradually alters the tea's flavour, aroma, and chemical composition as it ages.[4][5]

Originating from Yunnan’s ancient tea forests, Pu-erh tea was traditionally harvested for medicinal uses before becoming an important agricultural and commercial product through expanding trade networks.[5][6] It was historically traded along the Southwest Silk Road, or Tea Horse Road, which extended from southern Yunnan to the Tibetan Plateau[7]. During long-distance transport, exposure to changing temperature and humidity allowed oxidation and fermentation to occur, naturally aging the tea and creating a more mellow flavour over time.[4] Loose tea leaves were traditionally compressed into forms such as bricks and cakes to facilitate transportation, storage, and distribution across different regions.[5]

Beyond its role as a traded commodity, Pu-erh tea has also been incorporated into social and cultural practices in Yunnan, where tea is prepared and consumed during gatherings, celebrations, and traditional ceremonies. Today, Pu-erh tea remains associated with cultural events such as annual harvest celebrations and nature worship ceremonies.[5]

Initial Production of Pu-erh Tea

Pu-erh tea production in Yunnan, China. Image by Matthieu Lelievre, Wikimedia Commons (CC BY-SA 2.0).[8]

Traditionally, Pu-erh tea leaves are hand-plucked, with young shoots and tender leaves selected from tea trees during the harvesting season. Hand harvesting allows producers to choose leaves according to maturity and quality, whereas modern tea agriculture increasingly uses handheld or mechanized harvesters to reduce labour requirements and increase harvesting efficiency.[4] However, mechanical harvesting is less selective and may collect leaves of less uniform maturity. After collection, the fresh leaves are spread to reduce moisture, then heated in a process known as sha qing (“kill-green”) to limit enzymatic oxidation.[9] The softened leaves are rolled and subsequently sun-dried to produce mao cha ("rough tea"), the basic material used for further Pu-erh production.[5] Traditional processing relies heavily on manual pan-heating, hand rolling, and natural sun-drying, whereas modern commercial production increasingly uses mechanical equipment and more standardized processing conditions to improve efficiency and consistency.[10]

Safety concerns during production include pesticide residues, microbial contamination, and fungal metabolites. Because microorganisms contribute to Pu-erh fermentation and aging, bacterial and fungal populations can change substantially during storage.[10] Regulation of these concerns differs between markets. In Canada, imported tea must meet Health Canada food-safety requirements and CFIA import controls, including requirements related to contaminants and pesticide residues.[11] In China, tea production is subject to national food-safety requirements covering tea products, pesticide residues, processing hygiene, and production controls. China’s market regulator also identifies pesticide residues, heavy metals, sanitation, processing conditions, and storage as important safety-control points in tea production.[12]

Pu-erh Tea Aging Process: Microbial-Driven Chemical Changes

Camellia sinensis var. assamica, the tea plant variety used to produce Pu-erh tea.[13] Image by Krzysztof Golik, Wikimedia Commons (CC BY-SA 4.0).[14]

Two primary types of Pu-erh tea are produced: raw (sheng) Pu-erh, which undergoes slow natural aging over many years or decades,[15] and ripe (shou) Pu-erh, which experiences accelerated fermentation through wet piling (wo dui). Wet piling (or pile-fermentation), a microbial-driven process conducted under high-temperature and high-humidity conditions, reflects the principles discussed in Lesson 9.3, where microorganisms drive biochemical transformations within fermented foods. These transformations contribute to the characteristic chemical profile of ripe Pu-erh, which is distinct from that of raw Pu-erh. Although microorganisms also influence the aging of raw Pu-erh, these changes occur gradually over extended storage periods rather than during an intensive fermentation stage.[10] Typically, ripe Pu-erh undergoes pile-fermentation for more than 35 days under controlled conditions, including high temperatures (35–55°C) and high relative humidity (approximately 85%) before storage.[16]

Compared with aged raw Pu-erh, ripe Pu-erh contains lower catechin levels and higher concentrations of gallic acid and caffeine after microbial fermentation.[17] Catechins and gallic acid are phenolic compounds that contribute to tea taste characteristics, including bitterness and astringency.[18][19] Beyond taste-related compounds, differences in processing also influence the aroma profiles of raw and ripe Pu-erh. Raw Pu-erh is commonly described as having floral, malty, green, or woody aromas, whereas ripe Pu-erh is associated with earthy, stale, or creamy aromas.[13] As introduced in Lesson 3.2, flavour arises from both taste and aroma (smell). In Pu-erh tea, differences in flavour therefore reflect both taste-related compounds and aroma profiles.

Of 465 metabolites identified in ripe Pu-erh, some compounds increased while others decreased depending on the influence of microbial activity and moist-heat conditions during pile-fermentation. Microbial activity affects the flavour and aroma of ripe Pu-erh by producing enzymes that accelerate the degradation and transformation of flavonoids, flavonols, and lipids. In particular, microorganisms have an exclusive influence on lipid metabolism pathways, contributing to the formation of volatile organic compounds (VOCs) associated with the aroma of ripe Pu-erh.[20] As both tea types continue to age in storage, ongoing biochemical transformations can further modify their sensory characteristics. For instance, raw Pu-erh can develop more predominant woody and herbal notes with time. Raw Pu-erh is generally believed to develop a more desirable aroma and greater market value with age due to increases in VOCs. However, VOC abundance does not increase indefinitely, as prolonged aging may lead to the degradation or reduction of certain compounds.[21]

Additionally, aging has a role in the visual development of both raw and ripe Pu-erh. One of the major biochemical changes during the production of Pu-erh is the oxidation and polymerization of catechins into larger pigments, including theabrownins.[22] The formation of theabrownins, which accumulate in mass during pile-fermentation, contributes to the brownish-red colour of ripe Pu-erh.[16][23] The colour's red and yellow hues continues to develop in intensity during aging.[24] In raw Pu-erh, a deepening of the tea colour is also observed, albiet more gradually, with colour changes from greenish tones toward orange and brown as aging progresses.[25]

  • Raw versus Ripe Pu-erh
  • Raw (sheng) Pu-erh fang cha (square tea brick). Image by Jason Fasi, Wikimedia Commons (CC BY-SA 2.5).[26]
    Raw (sheng) Pu-erh fang cha (square tea brick). Image by Jason Fasi, Wikimedia Commons (CC BY-SA 2.5).[26]
  • Ripe (shou) Pu-erh tuo cha (compressed tea ball). Image by Ash Crow, Wikimedia Commons (CC BY-SA 4.0).[27]
    Ripe (shou) Pu-erh tuo cha (compressed tea ball). Image by Ash Crow, Wikimedia Commons (CC BY-SA 4.0).[27]

Storage Conditions Influencing the Pu-erh Tea Aging Process

Storage conditions, particularly temperature and humidity, influence the metabolite and flavour changes that occur during the aging process of Pu-erh tea. While high temperature and high humidity can cause changes in taste and metabolites faster, colder and drier storage conditions generally result in a more stable flavour profile. Furthermore, it was found that higher temperatures and humidity cause greater changes to the metabolites compared to colder and drier environments. Resultantly, in colder and drier environments, the flavour profiles of the teas remained more stable compared to teas stored in hotter and more humid environments.[28]

The particular aroma that develops in raw Pu-erh tea during the aging process, which is not present in freshly produced raw Pu’er tea, is in part attributed to the environmental conditions in which the tea is stored. When raw Pu-erh tea is stored at lower temperatures and in drier conditions, the tea is shown to exhibit an increase in levels of carotenoid derivatives, and glycoside and phenolic volatiles, resulting in an aroma that is sweet, fresh and floral. When stored at higher temperatures and in humid conditions, the tea is shown to exhibit increased levels of methoxybenzene compounds, resulting in a more stale and woody aroma.[29] In comparison, ripe Pu-erh tea has a higher concentration of methoxyphenolic compounds due to post-fermentation in a hot, humid environment, resulting in the unique herbal and musty aroma.[30][31] A major contributor to the difference in aroma profile between ripe and raw Pu-erh tea is that methoxyphenolic compounds increase through oxidation during normal storage in raw tea compared to during the post-fermentation process in ripe teas.[29]

Effects of Storage Duration on Pu-erh Tea Quality and Safety

Longer storage times do not necessarily mean an increase in quality, as for both types of tea, polyphenol concentration increased throughout an aging period of 60 months before starting to decrease, while pathogenic bacteria were detected after 120 months of storage.[32] Additionally, it was found that ripe Pu-erh tea has higher levels of tea polyphenols compared to raw Pu-erh tea. In ripe tea, the fermentation process causes the oxidation and polymerization of polyphenols, whereas the milder aging process in raw tea results in fewer reactions.[29] Teas rich in polyphenols are associated with several health benefits, including the prevention of diabetes, cancer, cardiovascular disease, and neurological diseases.[33]

Storage duration affects the microbial population of Pu-erh tea, as bacteria and fungi are involved in its fermentation and long-term aging process. A study examining Pu-erh teas of different ages observed changes in bacterial and fungal communities, as well as the presence of potentially pathogenic bacteria in samples subjected to long-term storage. These microbial changes are particularly significant because Pu-erh tea relies on microorganisms during its characteristic aging process, while certain microorganisms may pose food safety concerns during long-term storage.[32] For this reason, storage duration must be considered in balancing product stability and food safety with the desired effects of aging. Consequently, aging time alone is not considered a definitive indicator of tea quality.

Packaging of Pu-erh Tea (Traditional versus Modern)

Inner packaging for Pu-erh tea cake. Image by Ash Crow, Wikimedia Commons (CC BY-SA 4.0).[34]

Traditional aged Pu-erh tea is commonly packaged using handmade paper and bamboo materials such as bamboo leaves and bamboo baskets which provide physical protection while also allowing some exchange of air and moisture during storage. These methods are associated with long term aging process of raw Pu-erh tea, during which microbial activity and chemical transformations contribute to changes in aroma, colour, flavour and bioactive compounds over time.[15][10][21][9][29]

Modern commercial packaging systems increasingly use protective barrier materials, including laminated films and moisture resistant packaging to minimize exposure to oxygen, odours and contaminants during transportation and storage.[35] These materials improve product stability and shelf life.

Conservation Challenges in Pu-erh Tea Production

Traditional Pu-erh production systems face several conservation challenges including increasing commercialization, changes in agricultural practices and loss of traditional ecological knowledge. The expansion of large scale production may reduce reliance on traditional cultivation and processing methods, while environmental pressures and changing land use can threaten the biodiversity of ancient tea forests and traditional tea growing landscapes.[1][6]

Preserving traditional Pu-erh production systems is important for maintaining genetic diversity among ancient tea trees, supporting sustainable agricultural ecosystems and protecting cultural heritage and processing knowledge developed by tea producing communities over generations.[1][6]

Pu-Erh Exam Question

Question: Which option explains the effect of long-term storage on Pu-erh tea?

A. Pu-erh tea quality (e.g., number of aroma-contributing compounds) and food safety always increase as storage time increases.

B. Long-term storage completely stops microbial activity in Pu-erh tea.

C. Long-term storage can promote desirable changes in Pu-erh tea’s quality, but these benefits may diminish with very prolonged storage, which can also raise microbial-related food safety concerns.

D. Temperature and humidity have no effect on Pu-erh tea quality in long-term storage.

Correct answer: C

Explanation: During storage, microbial-driven chemical changes contribute to the aging of Pu-erh tea, which can produce desirable changes in its quality, such as increases in aroma-contributing compounds. However, longer storage does not necessarily result in an increase of these desirable changes and may introduce food safety concerns associated with microbial activity. This question should be included on the FNH 200 final exam because it tests students’ understanding of FNH concepts, including food storage, microbial activity, and food safety, highlighting the paradox whereby storage conditions that facilitate the development of desirable qualities during Pu-erh aging can also contribute to undesirable changes over prolonged periods.

References

  1. ↑ 1.0 1.1 1.2 Saladino, D. (2022). Eating to Extinction: The World's Rarest Foods and Why We Need to Save Them. United States: Farrar, Straus and Giroux.
  2. ↑ OGBerserk. Pu-Erh Tea Round Brick. Wikimedia Commons, 17 Oct. 2025, https://perma.cc/B2GM-75Z2
  3. ↑ Royal Botanic Gardens, Kew. "Camellia sinensis var. assamica (Royle ex Hook.) Steenis." Plants of the World Online, 2026, https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:60454412-2
  4. ↑ 4.0 4.1 4.2 4.3 Ahmed, Selena, and John Richard Stepp. "Pu-erh Tea." Tea in Health and Disease Prevention, edited by Victor R. Preedy, Academic Press, 2013, pp. 59–71.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Ahmed, Selena, et al. "Pu-erh Tea Tasting in Yunnan, China: Correlation of Drinkers' Perceptions to Phytochemistry." Journal of Ethnopharmacology, vol. 132, no. 1, 2010, pp. 176–185.
  6. ↑ 6.0 6.1 6.2 Food and Agriculture Organization of the United Nations. (n.d.). Pu'er Traditional Tea Agrosystem, China. Globally Important Agricultural Heritage Systems. https://www.fao.org/giahs/giahs-around-the-world/china-puer-traditional-tea-agrosystem/en
  7. ↑ Yang, Fuquan. "The ‘Ancient Tea and Horse Caravan Route,’ the ‘Silk Road’ of Southwest China." The Silk Road, vol. 2, no. 1, 2004.
  8. ↑ Lelievre, Matthieu. “Making Pu'er Tea, Yunnan.” Wikimedia Commons, 22 Feb. 2002, https://perma.cc/9WR3-QGLM
  9. ↑ 9.0 9.1 Lv, Hai-peng, et al. "Processing and Chemical Constituents of Pu-Erh Tea: A Review."Food Research International, vol. 53, no. 2, 2013, pp. 608-618.
  10. ↑ 10.0 10.1 10.2 10.3 Pei, Dengyi, et al. "Dynamic Changes in Pu-Erh Tea during Pile Fermentation: Comparing Novel Plie Fermentation to Traditional Method." Applied Food Research, vol. 5, no. 2, 2025, pp. 101332.
  11. ↑ Canadian Food Inspection Agency. “Importing Food to Canada: Overview.” Government of Canada, 2019, https://inspection.canada.ca/en/food-safety-industry/toolkit-food-businesses/importing-food.
  12. ↑ State Administration for Market Regulation of China. “Production Licensing Review Requirements for Tea and Related Tea Products.” State Administration for Market Regulation, 2023, www.samr.gov.cn.
  13. ↑ 13.0 13.1 Wang, Sunan, et al. "Chemical Constituents and Biological Properties of Pu-Erh Tea." Food Research International, vol. 154, 2022, pp. 110899.
  14. ↑ Golik, Krzysztof. "Camellia sinensis var. assamica." Wikimedia Commons, 11 Nov. 2017, https://perma.cc/8XRZ-J5DG
  15. ↑ 15.0 15.1 Pedan, Vasilisa, et al. "Bioactive Compound Fingerprint Analysis of Aged Raw Pu’er Tea and Young Ripened Pu’er Tea." Molecules, vol. 23, no. 8, 2018, pp. 1931.
  16. ↑ 16.0 16.1 Ma, Cunqiang, et al. "Investigation and Dynamic Changes of Phenolic Compounds during a New-Type Fermentation for Ripened Pu-Erh Tea Processing." Food Science & Technology, vol. 180, 2023, pp. 114683.
  17. ↑ Zhang, Liang, et al. "Comparison of the Chemical Constituents of Aged Pu-Erh Tea, Ripened Pu-Erh Tea, and Other Teas using HPLC-DAD-ESI-MSn." Journal of Agricultural and Food Chemistry, vol. 59, no. 16, 2011, pp. 8754-8760.
  18. ↑ Scharbert, Susanne, and Thomas Hofmann. "Molecular Definition of Black Tea Taste by Means of Quantitative Studies, Taste Reconstitution, and Omission Experiments." Journal of Agricultural and Food Chemistry, vol. 53, no. 13, 2005, pp. 5377-5384.
  19. ↑ Chen, Yu-Hong, et al. "Effects of Phenolic Acids and Quercetin-3-O-Rutinoside on the Bitterness and Astringency of Green Tea Infusion." NPJ Science of Food, vol. 6, no. 1, 2022, pp. 8-8.
  20. ↑ Li, Tiehan, et al. "Exploring the Mysterious Effect of Piling Fermentation on Pu-Erh Tea Quality Formation: Microbial Action and Moist-Heat Action." Food Science & Technology, vol. 185, 2023, pp. 115132.
  21. ↑ 21.0 21.1 Ma, Bingsong, et al. "Revealing the Formation of Aged Aroma in Raw Pu-Erh Tea during the Storage through Comprehensive Two-Dimensional Gas Chromatography Coupled to Time-of-Flight Mass Spectrometry and Molecular Docking." Current Research in Food Science, vol. 10, 2025, pp. 101038.
  22. ↑ Wang, Teng, et al. "Changes in Sensory Characteristics, Chemical Composition and Microbial Succession during Fermentation of Ancient Plants Pu-Erh Tea." Food Chemistry: X, vol. 20, 2023, pp. 101003.
  23. ↑ Chen, Xiujuan, et al. "Formation, Physicochemical Properties, and Biological Activities of Theabrownins." Food Chemistry, vol. 448, 2024, pp. 139140.
  24. ↑ Bo, Nianguo, et al. "Metabolomic and Sensory Insights into the Aging Mechanism of Ripened Pu-Erh Tea Over Nine Years." Molecules, vol. 31, no. 11, 2026, pp. 1937.
  25. ↑ Xu, Jiayi, et al. "Characteristic Changes and Potential Markers of Flavour in Raw Pu-Erh Tea with Different Ageing Cycles Analysed by HPLC, HS-SPME-GC-MS, and OAV." Foods, vol. 14, no. 5, 2025, pp. 829.
  26. ↑ Fasi, Jason. Fang Cha. Wikimedia Commons, 27 Sept. 2006, https://perma.cc/4GDE-L5EX
  27. ↑ Crow, Ash. Pu-erh Tea Ball Cake. Wikimedia Commons, 24 July 2021, https://perma.cc/3EGM-LYYK
  28. ↑ Xu, Shanshan, et al. "Metabolomics Based on UHPLC-Orbitrap-MS and Global Natural Product Social Molecular Networking Reveals Effects of Time Scale and Environment of Storage on the Metabolites and Taste Quality of Raw Pu-Erh Tea."Journal of Agricultural and Food Chemistry, vol. 67, no. 43, 2019, pp. 12084-12093.
  29. ↑ 29.0 29.1 29.2 29.3 Zhou, Li, et al. "An Up-To-Date Review on “The Ultimate Destination of TeaEnthusiasts”: Pu’ Er Raw Tea" Food Reviews International, vol. 42, 2026, pp. 1041-1067.
  30. ↑ Lv, Shidong, et al. "Application of Gas Chromatography-Mass Spectrometry and Chemometrics Methods for Assessing Volatile Profiles of Pu-Erh Tea with Different Processing Methods and Ageing Years." RSC Advances, vol. 5, no. 107, 2015, pp. 87806-87817.
  31. ↑ Pang, Xueli, et al. "Comparison of Potent Odorants in Raw and Ripened Pu-Erh Tea Infusions Based on Odor Activity Value Calculation and Multivariate Analysis: Understanding the Role of Pile Fermentation." Journal of Agricultural and Food Chemistry, vol. 67, no. 47, 2019, pp. 13139-13149.
  32. ↑ 32.0 32.1 Tian, Jianqing, et al. "Bacterial and Fungal Communities in Pu'Er Tea Samples of Different Ages." Journal of Food Science, vol. 78, no. 8, 2013, pp. M1249-M1256.
  33. ↑ Khan, Naghma, and Hasan Mukhtar. "Tea Polyphenols in Promotion of Human Health." Nutrients, vol. 11, no. 1, 2018, pp. 39.
  34. ↑ Crow, Ash. Pu-erh Tea Cake. Wikimedia Commons, 24 July 2021, https://perma.cc/LH2G-6J4A
  35. ↑ Robertson, Gordon L. (2016). Food Packaging: Principles and Practice (3rd ed.). CRC Press.
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