Today we're touching on an ever-present subject in the world of tea.
There's one question that regularly appears in Path of Cha's mailbox, probably more often than any other:
Which type of tea contains the most / least caffeine?
If you have asked yourself (or others) about this, then go on reading. This blog post is for you! (you guessed it, it is more complex than naming one tea for each category).
What is caffeine – a brief introduction
Caffeine is a chemical compound, a purine alkaloid. Together with theobromine and theophylline, they form the three main alkaloids present in tea. Together with tea polyphenols and amino acids, it is also the third main component that determines the taste and quality of tea. Caffeine and tea polyphenols form the bitterness in tea. They have some differences, though. Tea polyphenols have an astringent and bitter taste. However, they are closely related to tea's sweet aftertaste, or Hui Gan (回甘). On the other hand, the bitterness of caffeine is definitive, without transforming into a sweet aftertaste. Lastly, the combination of caffeine and other substances (particularly from the group of flavines) can enhance the smoothness and refreshing feeling of tea.
Caffeine also acts as a stimulant for the human body. It stimulates the nervous system, increases the heart rate, and has a vasodilative action on the lungs and bronchi.
Is caffeine in tea and coffee one and the same?
In short, yes. Technically, caffeine was first discovered at the beginning of the 19th century by a German physician experimenting with coffee. 8 years later, joint research confirmed the presence of a similar ingredient in tea. Initially, it was named theine. It took the research team some time before they confirmed it's actually the same molecule. From then on, the common term 'caffeine' was adopted for the substance in tea and coffee.
It is important not to confuse "Theine" with "Theanine". As mentioned, theine is another name for caffeine found in tea, while Theanine usually refers to L-theanine – an important amino acid found in tea leaves.
Which one has more caffeine – tea or coffee?
According to Yan Zhen, master of tea science from the State Laboratory of Anhui Agricultural University, the amount of caffeine in tea accounts for 2.5% to 3.5% from the overall substances amount. For coffee it is 1% to 1,7%*.
BUT: Let's make a simple calculation. If we brew an average of 3g of tea into a 150ml cup, the tea will contain about 75-105mg of caffeine.
Alternatively, brewing 8.3g of coffee in a cup of 150ml will load us with 83-141.1mg of caffeine.
Judging by the above calculation, the average caffeine content in a cup of tea is 90mg, while the caffeine content in the same cup of coffee is a little above 112mg.
So, although tea contains more caffeine as an absolute value, it might provide less caffeine than coffee in terms of personal intake.
Furthermore, caffeine in tea might stimulate us in an entirely different manner than the one in coffee.
Caffeine in tea vs coffee tonic effect
We mentioned that the caffeine in tea is identical to that in coffee. Still, the effect and sensation caffeine in tea has on the human body can vary greatly from the one in coffee. What is the reason behind that?
That reason is called L-Theanine
Remember when we mentioned L-Theanine above? Ironically, it's often misused for theine, from which it is exactly the opposite!
L-Theanine is among the most important amino acids found in tea. While caffeine contributes to the bitter, astringent, and refreshing part, amino acids account for the sweetness and umami component of the tea taste. Furthermore, L-Theanine is a powerful neurotransmitter that modulates the effect of caffeine. According to a number of research, it impacts the serotonin and dopamine levels in the brain. Thus, it provides a mental focus, improves cognitive performance, and ensures a good mood boost. L-Theanine is also known for increasing the "alpha activity" in the brain. By doing so, it helps us deal with stress and puts us into a state of awareness. No wonder ancient cultures consistently used tea in meditation and spiritual practices!
Which type of tea is most / least caffeinated?
Do you want a short answer? Unfortunately, there is none :( When it comes to caffeine content in tea, it varies according to a number of factors – and six tea types is not among them. Imagine you harvest the tea leaves from the same bush. Then, you have them sent for processing to create three different types of tea – for example, green, white, and black. The final teas of all three types will contain the same levels of caffeine.
A study published in Issue 4'20 of the "China Tea Processing" compendium states that caffeine content in tea leaves doesn't change when stored at temperatures from -18C to 60C. That means that the usual storage and processing will not affect the caffeine content in tea (with probably one exception, which we will discuss later in the article). Therefore, from a production and processing point of view, the six tea types are not a factor in defining the levels of caffeine in finished teas.
That said, you can still estimate whether your tea is more or less caffeinated by taking into account several important factors. Let's go through them one by one.
The real factors behind caffeine in tea
Tea tree variety
Levels of caffeine may vary across tea tree’s different varieties. Currently, the variety with the highest measured caffeine amount is the original Camelia Sinensis var. Sinensis. Its caffeine content accounts for 2,8% of the dry leaves weight**. Two Yunnan large-leaf varieties (namely, Camelia Sinensis var. Taliensis and Assamica) follow with 2,5% and 2,4% respectively.
There is a common understanding that the Yunnan large-leaf tea tree contains more caffeine; however, this probably stems from the unusually bitter taste and strong Qi (气) that some Yunnan varieties possess. The bitter taste can also mean a high content of another group of substances (namely, polyphenols) and is not related to caffeine levels. This is also related to Pu-erh's Hui Gan property, as, as we mentioned before, the bitterness of caffeine doesn't transform into returning sweetness. You can read more about Cha Qi and why it makes tea potent here.
Factors such as the soil, sunshine, moisture, altitude, and amount of shade in the tea tree growing environment will all affect the content and proportion of the substances contained in the tea.
Fertilization artificially enhances the plant's development, including the accumulation of inner substances in tea leaves. Fertilized tea is known to contain higher caffeine amounts than naturally grown ones.
Areas with greater sunlight exposure are known to produce tea richer in caffeine and polyphenols, making the tea' taste more bitter and astringent. Alternatively, growing in cloudy, misty areas increases the amino acid content in tea, giving it a sweeter and fresher taste.
The tea trees in mountainous regions grow at a slower pace. However, their root system is stronger. It penetrates deep into the soil, absorbing a rich amount of nutrients. This kind of tea has a refreshing, sweet taste and rich aroma without being excessive in caffeine. On the contrary, tea in the lowlands grows faster due to a higher temperature. What it can't make up in aromatic substances and amino acids, it stacks up in polyphenols and caffeine. Such tea has a sharp, pungent taste with higher bitterness and astringency.
Tea plant parts
Different parts of the tea tree contain different levels of caffeine too. A common misunderstanding is that teas made from buds, like some green teas, are less caffeinated than teas using more mature leaves, like Hong Cha. In fact, while the plant is growing, it makes sure to send the largest amount of nutrients to its most actively growing parts. As the buds are the ones that make the plant grow, they get the highest amounts of all inner substances, including caffeine. Thus, bud-only teas are more caffeinated than other teas.
Here is a summary of caffeine distribution according to the tea tree parts***
Tea tree part caffeine (%)
First leaf 1,68
Second leaf 1,02
Third leaf 0,98
Fourth leaf 0,51
Fifth leaf 0,81
Sixth leaf 0,65
Seventh leaf 0,38
Eighth leaf 0,39
Ningth leaf + bud 0,47
Stem (upper part) 0,09
Stem (mid part) 0,07
Stem (lower part) 0,01
Regularly trimmed trees try to make up for what's lost by increasing the supply of inner substances to the newly formed shoots. Thus, tea leaves from bushes that are subject to trimming are higher in caffeine than those that are not.
There are two existing theories. According to one, spring tea is higher in caffeine, as the growth rate is highest and most quick during springtime. Alternatively, due to Chinese summer being excessively hot and dry, there is also a theory that the summer tea stacks up most caffeine due to excessive sunlight and insufficient moisture. Either way, tea growing in the warmer seasons would contain more caffeine than the one harvested during autumn or – where that applies – in winter.
Last but not least – caffeine is highly soluble in water. That means the longer we steep the tea leaves, the higher the caffeine amount in our tea soup.
Is Pu-erh really the most caffeinated tea?
We mentioned before that Yunnan large-leaf variety reputedly contains more caffeine than the regular Sinensis variation. Indeed, there is some research that confirms it, while other claims the opposite****. If we speak about the finished tea, Sheng Pu has a reputation of a very potent tea with high caffeine amount, intense taste, and strong energy. However, Ripe Pu-erh, although produced from the same variety, has a very different impact on the human body.
In fact, cooked Pu-erh is the only tea Chinese traditional doctors recommend as suitable to drink late in the evening or before falling asleep.
There are a couple of theories as to why it is so. One claims that the internal transformation of caffeine during the fermentation phase prevents it from binding to the nervous system, so it doesn't affect sleep. Another suggests that the free-form caffeine binds with other substances during the cooling stage. When we drink the finished tea, free-form caffeine is less, and the caffeine-based compounds take longer to release the caffeine in the body. Thus, the effect on the body is more subtle. Either way, according to TCM, cooked Pu-erh is the only major tea type suitable for late-night drinking. Give it a try and see for yourself!
* Yan Zhen, State Key Laboratory of Tea Tree Biology and Resource Utilization, Anhui Agricultural University
** Caffeine and related purine alkaloids: Biosynthesis, catabolism, function and genetic engineering, Hiroshi Ashihara, Hiroshi Sano, Alan Crozier; Department of Biological Sciences, Graduate School of Humanities and Sciences, Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan Botanical Institute, Stockholm University, Stockholm 106 91, Sweden; Graham Kerr Building, Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
*** Yan Zhen, Huang Jianyao, Gao Lu, et al. Research Progress in Biological Metabolism of Caffeine in Tea Trees [J]. Chinese Tea, 2020, 42(7): 1-7.)
**** Astill, Conrad, et al. (2011)