Tea also has a special place in Yunnan's history. It served as the main driver of the Ancient Tea and Horse Road (茶马古道), which for centuries put Yunnan at the center of an intricate trade network connecting Han China, Tibet, Southeast Asia and India.

Despite the fact that people have been drinking tea for millennia, it is still infused in myth and mystery. Its properties and the health benefits for regular drinkers are unclear – for now. Ethnobotanist Dr Selena Ahmed, co-author of the book Tea Horse Road spent four years researching tea in Yunnan for her doctoral study at The New York Botanical Garden and City University of New York and is currently studying the effects of tea on human health.

We recently spoke with Dr Ahmed about tea's relationship with people and the earth:

GoKunming: How did you become interested in tea?

Dr Selena Ahmed: I am interested in examining human interactions with the environment. During my doctoral study, I was seeking to research a plant resource that humans have an extensive history managing. I was specifically looking to study a plant with global relevance.

A friend and colleague, Dr Louis Putzel, told me about the tea trees and diversity of Camellias in Yunnan in spring 2006. I had been drinking tea since childhood and had visited tea gardens in Taiwan and Darjeeling but had never thought of examining tea as an intellectual pursuit.

That summer I was in the Venezuelan Amazon and Dominican Republic carrying out research, teaching field methods, and looking for a project for my doctoral study. Infinite interesting potential projects! Upon returning home I met with my doctoral advisor, Dr Charles M Peters, at the New York Botanical Garden. We were drinking tea and he told me about the forest tea populations at his study site in Myanmar, and the origin of tea still being debated.

It was over that cup of tea that I decided to study the world's most widely consumed beverage - after water. Yunnan seemed the obvious place to do this, being the center of diversity of tea resources and home to mountain-dwelling cultural groups that manage tea trees in agro-forests. I had no idea at that time how fascinating I would find this endeavor. I am continuously blown away by it all.

GK: How much time have you spent in Yunnan doing field research?

Ahmed: I first visited Yunnan in the fall of 2006. The autumn harvest season was wrapping up. It was a reconnaissance visit and I had done minimal literature research on Yunnan before visiting. I rode down to Xishuangbanna with a team of botanists from Kunming Institute of Botany and then went off to visit some mountain communities. I was completely taken in by the lives and landscapes around me. An ethnobotanist's delight!

I have returned to Yunnan once or twice a year since then and stayed for a few weeks to several months each visit. My longest stretch in Yunnan was six months. There are some spots in the mountain communities that keep calling me back.

GK: What are some of the most interesting things about the relationship between tea and people that you've discovered while in Yunnan?

Ahmed: I find some of the most interesting aspects about the relationship between tea and people to be the associated biodiversity, cultural practices and knowledge. It is such a rich and dynamic relationship.

The relationship between tea and people particularly fascinates me because there are varied outcomes based on management practices. For example, in some cases human interactions with the environment through tea production have resulted in the loss of plant species and genetic diversity. This is the case in many terrace tea gardens.

At the same time, human interactions with the environment through tea production have maintained and even enhanced plant species and genetic diversity. I have found this in some indigenous tea agro-forests and mixed crop fields. I feel very privileged to have had the opportunity to document aspects of this evolving relationship.

Another interesting aspect of the relationship between tea and people is the inextricable link between environmental and human health. Healthier tea systems from an ecological perspective provide greater health benefits to humans. We have much to learn from communities that manage indigenous tea agro-forests – for agriculture, for forest management, for health and nutrition and for sustainability.

GK: Are there certain ethnic groups that are associated with specific steps in the production of tea?

Ahmed: The socio-linguistic groups that I associate with growing and harvesting tea are the Bulang [Blang], Wa, Akha [Hani], Lahu, Yao, Hmong [Miao], Jinuo and De'ang.

Many communities of these groups grow tea in agro-forests and mixed-crop fields. Some of these groups also have distinct tea processing and preparation. For example, upland Bulang communities ferment pu'er in underground pits for several weeks to years and eat the leaves as an accompaniment or salad.

The Bulang also eat fresh tea with nanmi, a condiment made of several spices, and elder Bulang women chew tea leaves with a mixture of betel nut [Areca catechu L.; Arecaceae], lime, and other plants.

Fresh and fermented tea leaves are particularly eaten during celebrations such as the annual harvest and nature worship ceremony in tea agro-forests. The Jinuo roast tea leaves that are mixed with spices and wrapped in banana leaves.

I associate lowland communities such as the Han Chinese to be active in processing steps of steaming and pressing loose dried tea into pressed bing [round, flat cakes] or in post-fermenting.

GK: How does tea affect the soil in which it is grown?

Ahmed: Like other plants, tea plants penetrate the soil, uptake nutrients and change the chemical properties of the soil. Tea plants are continuously impacting the nutrient and other chemical properties of soil in which they grow.

This relationship is variable on several factors such as the age of tea plants. For example, older and larger tea plants generally uptake more nutrients from the soil and have higher nutrient stocks in their standing biomass compared to younger smaller tea plants in the same garden.

GK: What goes on in the drinker's body during a pu'er gongfucha session?

Ahmed: The drinker is greeted by a complex sensory experience during the pu'er gongfu cha session. Volatile aromatic compounds first hit the nose and awaken the mind. Then phenolic catechins, methylxanthines, amino acids and sugars hit the tip of the tongue, envelop the entire mouth, and have a peak taste sensation in the throat.

Once pu'er is ingested, tea compounds such as the catechins and caffeine enter the body, biotransform and metabolize. Most of these compounds are rapidly cleared from blood in several hours where they are excreted via bile to the colon and eventually in urine. A small percentage of the consumed compounds make their way to the blood stream. Different compounds in pu'er behave differently and are found in various concentrations in the blood.

GK: There are a lot of different claims of health benefits swirling around pu'er tea... what are the primary proven benefits of regularly drinking pu'er tea?

Ahmed: In vitro and animal studies have demonstrated pu'er to have a range of health protective effects including anti-atherosclerotic activities, anti-allergic, antioxidative, anti-fibrotic, hypolipidemic, hypocholesterolemic effects, plus anti-obesity, anti-viral, anti-mutagenic, anti-microbial, anti-carcinogenic, anti-diabetic and neuroprotective effects.

Studies have also found pu'er to prevent tooth decay and ulcers, control halitosis, cure stomach disorders, improve bacterial flora, increase bone density, and protect against UV rays.

Human studies have revealed that tea catechins are not well absorbed by the body and epidemiological and clinical studies examining the association between tea consumption and risk of chronic disease are inconclusive. However, clinical studies have substantiated green tea extracts as the source of the only botanical prescription drug approved by the United States Food and Drug Administration. Further study is certainly warranted to better understand the health protective properties of pu'er.

GK: What's the healthiest kind of pu'er tea: shengcha or shucha?

Ahmed: It is difficult to make generalizations regarding pu'er's phytochemical constituents and potential health benefits given the large diversity of production and consumption practices of tea and the varied outcomes in the human body.

The polyphenol catechins, the primary phytochemicals responsible for the health claims of green tea, are highest in concentration in fresh leaves. As leaves are heated, rolled, and dried during processing of shengcha, the catechins compounds decrease. However, processing of green tea types such as shengcha is beneficial for stabilizing and increasing the shelf life of catechins by deactivating the enzymes responsible for oxidation.

Pu'er constituents, as in other tea types, undergo degradation, oxidation, epimerization, and polymerization reactions during storage as leaves interact with ambient oxygen, moisture, light, and temperature fluctuations. There is significant reduction of catechin levels within six months of storage.

That said, the degradation and oxidation of catechins during storage result in the formation of new constituents with a unique taste and potential health properties. This is also the case with shucha, where the processing involves oxidation processes and fermentation processes with microbial interactions.

GK: What's your favorite kind of tea?

Ahmed: Loose processed shengcha from Yunnan's agro-forests makes me smile. I love the high-octane bittersweet flavor. Wherever I am, it transports me to the tea mountains where it was produced. I mostly drink shengcha from my study sites. I can taste those tea gardens and see the families that processed the tea. It's an awesome taste journey.

GK: What projects are you working on now?

Ahmed: I am currently working with a team at Tufts University in Boston to assess impacts of climate change on tea production quality and associated farmer perceptions. This work builds on findings arising from my doctoral study in Yunnan and incorporates new models, research tools and ideas. I look forward to long-term research in the area!

Top image: Michael Freeman

Middle image: Yang Yahan

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