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Tea & Caffeine

We are very lucky that we are asked a great number of specific questions in our teahouses. One of the most common topics is caffeine.

This blog will look to answer these questions and a few more. Firstly, all true teas (teas made from the Camellia Sinensis plant) contain caffeine. Caffeine is a naturally occurring stimulant that is soluble in water and extracted when brewed. Teas in general have around a third of the caffeine of a similar serving of coffee, although as we will see there are many factors which effect this. Simply put, it is not possible to generalise about caffeine levels in tea. However, there are some factors which allow an informed decision to be made. The best explanations I could find were in an article by tea expert Nigel Melican and in Jane Pettigrew's book 'The New Tea Companion' which you can buy online or at Comins tea houses.  Before getting into the details it useful to understand that caffeine is a methylxanthine, a compound that is used by plants and humans as a pesticide.

This natural insect repellent is produced by the plant to discourage the nibbling of new buds or the damaging of shoots. This helps explain why many of the various factors explored below effect the level of caffeine in your tea.  So lets get into the detail :

Factor 1 THE PLANT :

a. The Variety : The two varieties of Camellia Sinensis (the tea plant) are 'Assamica' and 'Sinensis' meaning 'from Assam' and 'from China' respectively. The Chinese 'Sinensis' has smaller leaves of 5-12cm with bushes growing up to 1m high while the Assam 'Assamica' has larger leaves of up to 20cm with trees growing up to 20 metres.   In general Sinensis plants are lower in caffeine than Assamica ones. So African teas that are mainly Assamica variety are higher in caffeine than Chinese ones. 

Camellia Sinensis bush : Source

b. The varietal : Taking this to a smaller scale we can look at the different varietals (or bush varieties) of the tea plant. This also includes the different cultivated variations (cultivars) which have been developed by farmers over time. There are variations in caffeine levels between all these, caused by the plant evolving over time to best suit its environment. This change can also be controlled by the farmer, by his or her propagation of plants and the choosing a certain plant because of a desirable characteristic (increased resistance to insects for example).

c. The Altitude : Another controlling factor is the altitude at which the plant grows. The higher the growing environment the lower the caffeine level, presumably due to the reduced numbers of insects. This variation in insect numbers may also be why growing season is also a factor. The faster growing seasons of spring and summer produce greater levels of caffeine. Fewer insects are present in colder times.

Tea Fields : Taiwan : Source Comins

d. How the plant is grown : The final element concerned with the plant itself is how it is grown in the first place. If it is from clonal vegative propagation (a cutting fixed to root stock) rather than planted as a seedling, caffeine levels can be 100% higher. A real life comparison is between new planting in Africa and old seedling planting in Asia. Eg older leaf, China type seedling bushes, under fertilised in the autumn season = low caffeine levels of 1-1.5%.  This is compared to well fertilised, fast growing young tips African in  clonal plants which yield caffeine levels of 5-6% source Nigel Melican

Factor 2 HUMAN IMPACT :- 

a. The actions of the grower : The actions of the grower can also impact on caffeine levels. When a plant is given a lot of nitrogen fertiliser caffeine is higher. This is common practice in Japan. Staying in Japan, another human action increases levels. This is the practice of leaf shading whilst the plant is growing. Leaves for Gyokuro, for example, can be shaded for around twenty days before picking. This increases caffeine but also increases an amino acid called L-theanine. L-theanine has the affect of moderating the release of caffeine, so the higher amount if caffeine is released over a longer period of time.
Tea growing in Uji : Here you can see the nets that will be placed over the tea : Source Comins
b. The part of the tea plant that is picked is important when looking at caffeine. A tea made from leaf buds and tips has more than one using just leaf only. Young leaf buds have the highest concentration as this is the time when it needs the most protection from insects. It also matters how the plucking is done. The higher the standard the higher the caffeine.
c. Production methods / processing Once the leaf is picked it's caffeine content can still be changed. The instant the leaf is picked it starts to wilt, a process called withering. Slow withering at a moderate temperature results in the highest caffeine. A long wither also means higher caffeine. Another step in the processing of some teas, oxidation, reduces caffeine. Oxidation is the what causes a tea leaf to become darker and more astringent in taste. Green teas are not oxidised, whereas black teas are fully oxidised.
d. How you prepare the tea Once the processing is finished and the tea is in your cup you can still impact on the caffeine level. The higher the water temperature you use the higher the amount of caffeine released and the faster the speed of extraction.
e. Decaffeination process : The last area to look at briefly is decaffeination of tea. I say briefly because there is a great deal that can be written- a later blog perhaps. One important thing to know is that none of the processes available completely rid the leaf of caffeine. They can, however, leave chemical residue behind, greatly reduce the flavour or make a cheap tea expensive. It is far better to explore the various caffeine free infusions available. Further to this, the '30 second wash' decaffeinating method does not work - Nigel Melican has some great figures to prove this, if you require more detail 
In conclusion, without chemically measuring each spoon of tea leaf you use, it is impossible to say how much caffeine there is in it. All you can hope to do is make a rough estimate, but for this you need to know where you tea is from, how it was grown, processed, picked and brewed.
We, as a company, aim to know all these things, and give this information to you. However, this can be hard to process! The alternative is seeing how it affects you. We drink our teas regularly and over time have developed a knowledge of how they affect us all. Of course the effect of caffeine is different for everyone, so my advice is that if you prefer your tea to relax rather than over stimulate, ask us which teas to avoid and which to try. Give them a go and if they are too much then don't have them again. Also be aware that tannin can have an effect on you also...
References :
Nigel Melican CAFFEINE AND TEA: Myth and Reality
Jane Pettigrew : 'The New Tea Companion'
Ultimately, find out more about your tea, enjoy it and listen to your body. 

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  • Stephen on

    Interesting article that pulls together alot of information in one place… Thank you!
    As someone who is “sensitive” to caffeine, I’m intreagued by the caffeine wash ideas as I had hoped to find a way of enjoying some teas that are currently a wee bit too stimulating!

    I can’t get the Robert Milligan link to work (404)!?

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