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Tea

Would you miss it?

You can’t buy happiness, but you can buy tea and that’s kind of the same thing. -Anon

The proper, wise balancing of one’s whole life may depend upon the feasibility of a cup of tea at an unusual hour. -Arnold Bennett

One day I decided to try to have a complete day without tea. I was quite shaken. I was quite disturbed. -Morrissey

What is tea?

 

Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of Camellia sinensis. After water, it is the most widely consumed drink in the world.

  • Camellia sinensis is an evergreen plant native to eastern Asia.
  • C. sinensis leaves are dark green with serrated edges, and a pointed tip.
  • Two major varieties are used for tea production - C. sinensis var. sinensis and C. sinensis var. assamica. Hundreds of cultivars (subtypes) have been developed by traditional plant breeding techniques.
  • C. sinensis is a tree under natural optimum conditions, but plants are pruned to shrub height when cultivated for ease of picking.
  • C. sinensis typically has a 100 year lifespan with a commercial span of about 60 years.
  • Tea is found in areas in with an annual rainfall of over 1200mm per year, and an average humidity level of 70 to 75%. Optimal temperature is between 13°-30°C .
  • Seasonal variation (and the reliability of seasons happening as predicted) is a contributing factor to the development of complex factors that differentiate varieties of tea.
  • Tea plants thrive best on deep, well-drained, permeable, and fertile soils.
  • Shade from hot sun and shelter from strong winds is preferred.
  • Tea leaves contain an extremely wide variety of compounds which give tea its gustatory/olefactory qualities. These include
    polyphenols (this group contains various flavonoids), amino acids, enzymes, pigments, carbohydrates, methylxanthines (including caffeine), minerals, and volatiles (with exotic sounding names like geraniol and nerolidol )

Tea as a global commodity

The global tea market had an estimated value of nearly 200 billion U.S. dollars in 2020.

CountryProduction (tonnes)1
China2,414,802
India1,252,174
Kenya437,000
Sri Lanka394,308
Turkey243,000
Vietnam240,000
Indonesia144,015
Myanmar102,404
World (approx) 6,000,000

Top tea importers are2

Pakistan
USA
Russia
United Kingdom
Saudi Arabia

Major tea growing countries of the world

Major tea growing countries of the world

 

Changes in tea yields over time

Changes in tea yields over time

Figures above are from Our World in Data. Examples on the page are interactive and offer historical information about yields in selected countries.


Factors which threaten the production of tea

Early research indicates that tea growing regions could decline in some parts of the world by up to 40-55 percent in the coming decades and the qualities, particularly for high end teas, could also change.3

We take tea for granted in many countries of the world. We just assume we can buy tea the tea that we favour anytime we want some. But climate change may deliver a new reality to us, one in which tea is not always going to be available. Physical factors such temperature and humidity will effect the growth of tea plants, and the delicate balance between predators and prey may be tipped out of what we regard as normal.

Physical factors

 

The term "terroir" describes the different environmental factors that contribute to the flavour and character of a product. It originated in the wine-making industry. The terroir for tea involves temperature, humidity, precipitation, altitude, aspect, light exposure, and soil.

Primarily, tea only will grow in places that meet their temperature, rainfall and humidity needs, namely places with warm, humid climates. The tea plant can handle a light frost but not heavy freezes or prolonged cold winters.

Similarly to climate, altitude can trigger stress responses in tea plants. This is because higher altitudes are exposed to higher amounts of UV radiation, as well as more dramatic variation in temperature, which triggers secondary metabolites in tea. The highest commercial tea operations are around 2,400m in elevation.

Interaction between aspect, altitude and rainfall.

Interaction between aspect, altitude and rainfall.

At higher altitudes, air pressure is lower, so air expands, and the process of expansion cools the air. The capacity for air to hold water vapour depends on temperature, and is lower at lower temperatures. Thus, as air rises, it expands and cools, and it cannot hold all its moisture, so this causes clouds to form, and often causes precipitation such as rain or snow. This explains why the windward (wind facing) side of mountains has high rainfall and the leeward (on the other side of the wind's source) side of mountains tends to be dry, a phenomenon called rain shadow. Tea, a water-loving plant, tends to be grown on the windward sides of mountain ranges.4

The soil that tea is grown in can vary dramatically and depends on the bedrock beneath the land. The mineral content of the soil is reflected in the tea. High rainfall can leach nutrients from the soil and thus influence its taste and value.

The sensitivity of tea plants to their growth environments is part of the appeal to connoisseurs who can discern taste characteristics that can be attributed to growth conditions. But that also makes the crop vulnerable to the effects of climate change. Variations in temperature and precipitation affect both tea yield, and the complex balance of chemicals that gives tea its flavour and potential health benefits. So less tea and/or lower quality tea may result.5

Case study - Assam (India)

Assam, a province of India, is found in the northeast of the country. It is responsible for growing about 50% of India's tea crop.

AssamMap

Assam region in India

In a 2018 survey of tea-farm workers in Assam, 88% of managers of plantations and 97% of smallholders said that adverse climate conditions were a definite threat to their tea-growing operations1. Climate change is pushing rainfall in Assam to the extremes, leading to an overall decrease in precipitation but with more instances of drought and heavy rain. The intense rains cause the erosion and waterlogging of soil, which damages root development and reduces the yield of the tea plants.5

The lower elevation and tropical latitude (compared to Yunnan, a major tea producing area in China) ensure that Assam is warm and humid almost year-round, with the Indian Monsoon providing a blast of torrential summer rain. The warm climate means that Assam tea, which accounts for 17 percent of all global tea production, sits right on the edge of tea’s growing range where rising temperatures are already being felt.6

Case Study - Yunnan (China)

Yunnan tea growing region in China

Yunnan tea growing region in China

The world renowned Yunnan tea growing region is located in the south west of China.
In Yunnan, farmers have told Ahmed (an ethnobotanist at Montana State University studying the region) that the quality of their tea is declining. “That really impacts the livelihoods of these farmers.” Ahmed has linked the decrease in tea quality to the monsoon season’s earlier start. The decline is partly attributable to a dilution of the chemicals that help to flavour tea — the leaves take in more water from the extra rainfall. But the effects on chemicals that have potential health benefits are more complex. When the monsoon season began earlier and temperatures were higher, Ahmed found that although the overall amount of phenolic compounds in tea increased, the levels of certain such chemicals decreased. She also showed that affected tea had less antioxidant activity — highlighting a possible negative effect of earlier rains on tea’s potential health benefits.5

Pollinator problems

Only relevant for tea variety breeding. Tea for field planting is propagated vegetatively i.e. cloning a plant via cuttings.

Pests and diseases

Partial list of organisms which attack Camellia sinensis
OrganismGroupingComments
AphidInsectSuck sap from leaves. Also maybe vectors of microbial diseases.
ThripsInsectSap suckers and disease vectors. may cause leaf distortions.
Tea Mosquito BugInsectAnother sap sucker
ScaleInsectYet another sap sucker.Has a waxy covering over its body.
WeevilsInsectLeaf chewers.
White flyInsectSap suckers
MitesArachnidMay cause blisters or galls on leaves
Sooty moldFungusBlack sticky mycelium feeding on aphid exudations.
Dieback CankerFungusLeaves on affected branches suddenly turn yellow and wilt.
Phytophera root rotFungusCauses leaves to wilt, discolor, remain undersized, and drop prematurely. Persists in soils for long periods.
Leaf gallFungusCauses leaves to become thickened, distorted, and crisp.
Algal leaf spotAlgaAbundant moisture, high temperatures, and direct sunlight favor algal leaf spot infections which will be most damaging on slow-growing, already weakened plants.
Leaf mosaic diseasesVirusInfected leaves may become discolored, distorted, spotted, streaked, or stunted

Climate change can alter the balance between plants and those organisms that prey on them. e.g.

  • Poor soil drainage, and exposure to relatively high temperature and humidity predispose tea plants to infection by algal leaf spot.7
  • Plants with a dieback/canker infestation show more symptoms during hot, dry weather.8
  • Changes in climate are influencing the abundance of insect pests. Higher temperatures enable insects that attack tea plants to survive winter, giving them more time in which to reproduce. Certain combinations can lead to immense explosions of pest numbers which can render a large proportion of the crop unusable.

What can we do about it?

Since the 1950s, agricultural systems have experienced gradual systematic changes in average climate conditions including unprecedented multi-decadal warming, increased inter-annual variability of the Earth's surface temperatures, changes in average precipitation, greater weather variability, and more extreme weather conditions.9

Solutions involve scientific, technical, social, legal and economic factors to varying degrees.

Quantity vs quality

Various studies have examined how the suitability of current tea growing strongholds will be effected by climate change. It is thought that there will be significant changes in the distribution of suitable areas.10 This is more of a problem for Camellia sinensis than many other crops, as it take takes years to get tea plants established and grown to a point where they are productive.

Planting a tea bush is a decades-long investment, one not easily moved or replaced like annual crops. That means to prepare for future changes, farmers and companies need to act if not now, then soon, if the tea in your mug is going to be there in the future.11

Not only do we have problems about the amount of tea that can be produced, we also need to consider the quality of teas available.

Mitigation and resilience responses

The problem of excessive water is being tackled by drainage , but this is a problem in extensive plantations this can be extremely difficult to achieve, not to mention expensive. Too much drainage, and bushes are left vulnerable in times of drought. Mulching is used to protect plants in times of drought. Cover plants are used to enhance soil quality and shade trees are used in some regions to help control sun exposure. Agroforestry in particular is recommended for areas growing tea in monocultures.

Pest management can be improved by changing from carpet bombing style eradication to more sophisticated techniques such as
- selective pesticides
- better management techniques such fine tuning picking times
- biological control which involves deliberate release of pests/diseases specific to the pest of the tea plants

Mitigation strategies include calculating and reducing greenhouse gas emissions on the farm, and facilitating the creation of carbon sinks. However, the tea industry is not a major CO2 polluter, so its ability to influence overall emissions is quite limited.

Genetic variability

As tea plants are commonly propagated by using cuttings, all plants in a given planting may be clones ie genetically identical and chosen for resistant to a a certain pest or tolerant of a certain sub-optimal physical condition. This can be a disaster though if conditions change and this genotype does not suit the plants to the new prevailing conditions. It is possible to introduce diversity into plantations by using conventional breeding techniques to produce variability into the genetics of the crop plants. In this case, seedlings are used rather than vegetative clones.

One approach that is being pursued vigorously is bioengineering of the C. sinensis genotype. While faster than conventional crossbreeding programs, this could result in patents being registered on new genotypes generated in labs with all the issues associated with ownership, costs and management. These issues are often underestimated in the rush to find a technofix. See12,13 This is often detrimental to small scale growers, and can result in bitter long-term legal turmoil.

All this change depends on research, education, plus stakeholder involvement at the grower and industry levels.
Selena Ahmed, an eminent tea industry researcher sums it up well

Foster cross-sector collaboration between researchers, practitioners, producers, and policy makers to develop evidence-based adaptation strategies that reduce vulnerability of food systems to shifts in crop quality toward supporting sustainability.14

For detailed examples of such actions, see the Ethical Tea Partnership website.

And there are those of us who see global climate warming as requiring high level government environment intervention to rescue the whole earth.

  • Consider who you vote into power in your country
  • Consider your own consumption patterns and who you buy from
  • Consider the future and what you want it to look like

 

Acknowledgement of issues not covered on this page

The social effects of change for small farm-holders, the politics of the producer countries, the exploitation of children's and women's labour conditions

Information starting points for more information about societal aspects of tea.



Bonus: The journey from plant to commodity

Harvesting

The plants are kept trimmed at a convenient height for picking.
This also promotes a multi-stemmed plant form which increases the yield of usable leaves.
Usually, the tip (bud) and the first two to three leaves are harvested for processing.
This tip picking is repeated every one to two weeks.

Women picking tea in an Assam garden

Women picking tea in an Assam garden

Bringing in the crop

The pickers bring in their baskets for weighing.

These are amalgamated in to a bale and transported to the drying shed.

Bale contents are inspected.

Leaves transported to drying shed

Leaves transported to drying shed

Spreading

The leaves are placed on long trays in the drying sheds.

Then they are spread out in  shallow layer.

The purpose of this is to dry the leaves out.

Tea leaves spread out

Tea leaves spread out

Processing techniques

Selective application of processes
These processes may include
- withering
- rolling
- fermentation
- shaking
- drying
- blending
- flavouring

Various processes to produce different styles.

Various processes to produce different styles.

Packaging and distribution

Once tea is processed, it can be packaged in
- loose bulk containers
- loose in boxes
- loose in tins
- in boxes of tea bags
- in compressed form such - as bricks or pellets
Packaging may occur near the origin point or at the destination for shipped teas.

Nerada Black pack of tea bags

Nerada Black pack of tea bags

  1. https://www.atlasbig.com/en-in/countries-by-tea-production []
  2. https://www.worldstopexports.com/tea-imports-by-country/ []
  3. https://www.scientificamerican.com/article/global-warming-changes-the-future-for-tea-leaves/ []
  4. https://ratetea.com/topic/climate-geography/55/ []
  5. https://www.nature.com/articles/d41586-019-00399-0 [] [] []
  6. https://www.scientificamerican.com/article/global-warming-changes-the-future-for-tea-leaves/ []
  7. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-33.pdf []
  8. http://camelliasaustralia.com.au/cultivation/ongoing-care/pests-and-diseases/ []
  9. https://doi.org/10.3389/fpls.2019.00939 []
  10. https://www.mdpi.com/2073-4395/10/10/1536 []
  11. https://www.scientificamerican.com/article/global-warming-changes-the-future-for-tea-leaves/ []
  12. Climate-Ready Crops: The Pros and Cons []
  13. Vandana Shiva, Stolen Harvest: The Hijacking of the Global Food Supply" []
  14. https://www.frontiersin.org/articles/10.3389/fpls.2019.00939/full []