I recently read an online article, supposedly vetted by experts, that claimed that white tea has no caffeine. Yeah.
Add that to misleading articles arguing that x tea has less—or maybe more—caffeine than y tea and you understand why people are confused about caffeine levels in tea.
To be sure, discussing caffeine in tea is not as straightforward as that of coffee. For coffee, we can calculate how much caffeine there is and that’s pretty much it.
When we talk about caffeine in tea, however, we must also factor in the amino acid L-theanine because these two constituents of tea work in balance—the caffeine stimulates while the theanine relaxes (by significantly increasing alpha wave activity in our brain).
To decide, then, to what extent a particular tea might keep us up at night due to its caffeine level, we also need to know how much theanine is counteracting or blunting that stimulus. Complicating the issue, we also need to understand that caffeine and theanine work synergistically as far as attention goes. The net effect is often referred to as a calm alertness.
But then we also should realize that calculating these levels is the stuff of laboratory studies because we cannot generalize.
In referring to caffeine and theanine, the authors of one study say this:
The great variability of these two compound [sic] within the tea categories allows no discrimination of tea types based solely on theanine and caffeine quantification. (Boros et al. 2016)
To come to these conclusions, the team tested 17 commercial tea samples bought in tea shops in Hungary and Taiwan.
They noted that dry tea leaves that haven’t yet been processed contain 1–2% theanine (found as free amino acid) and 7–9% methylxanthines of which 3–6% is caffeine (Boros et al. 2016).
How the tea is processed affects theanine levels but not caffeine levels. How we brew our tea impacts both theanine and caffeine levels.
The researchers, as shown in my table below, found that white, green, and oolong tea contained similar levels of theanine whereas black tea contained less and pu-erh had none.
White, green, and black tea had similar caffeine levels whereas pu-erh had less. The caffeine level of oolong teas varied widely, which makes sense because oolongs have a wide range of oxidation levels, from “green” oolongs to those that approach black teas in oxidation.
According to these data, then, a person drinking black tea might more fully experience the caffeine because it’s less blunted by theanine.
With green tea, although the caffeine levels may be comparable to black tea, there is more theanine to counteract those stimulating effects.
And although pu-erh has the lowest caffeine average of the teas tested, there is no theanine to offset caffeine’s impact!
Therefore, the theanine to caffeine ratio “determines the degree of stimulant effect of tea drinks” (Boros et al. 2016).
But for a complete picture, we need to keep in mind that the effects of caffeine are also impacted by other xanthines, such as theophylline and theobromine, and by polyphenols, which bind with caffeine, slowing its absorption (another influencer on how we experience the caffeine in tea).
There is also an appreciable range of theanine in green teas when we include tea that’s been grown in shade (e.g., gyokuro, matcha, kabusecha). Sunlight converts theanine to polyphenols, so tea grown in shade retains more of its theanine than that grown in sunlight.
And, levels of caffeine and theanine in an individual tea may fall widely outside the averages.
Further, as Boros et al. noted, how we brew our tea directly impacts caffeine and theanine extraction!
All of this means that:
based on the analysis of caffeine and theanine content, it is almost impossible to categorize teas to the groups of white, green, oolong, and black major tea groups. The only exception is pu-erh tea, which is characterized by its negligibly low theanine content. (Boros et al. 2016)
So, be wary of generalizations on caffeine level, realize that theanine also impacts how we experience caffeine, and know that calculating just how much caffeine is in our cup is extremely complicated.
And if you’re wondering what factors determine the caffeine level in tea, there are a lot!
This variability makes the scientist’s job difficult. Boros’ team measured a limited number of teas, which is a drawback of the study. How they extracted the components vs how other studies do this also colors the results. And how on earth does anyone compensate for all the factors in this list?!
- Type of tea plant (C. sinensis var. assamica has more caffeine than C. sinensis var. sinensis)
- Origin of plant (clone has more caffeine than seedling)
- Age of plant
- Stress on the plant (e.g., caused by pests)
- Soil conditions (e.g., higher nitrogen level means higher caffeine level)
- Growing season (the faster the plant grows, the more caffeine)
- Amount of shading the plant receives (shading increases the caffeine level, but also increases the theanine level, which offsets the stimulant effects of caffeine)
- Which leaves are plucked (buds and young leaves have more caffeine)
- How the leaves are processed after plucking (e.g., duration and temperature of withering, duration of oxidation)
- Particle size (e.g., fannings vs whole leaf)
- Brewing, which includes:
• temperature of water
• amount of tea
• method of brewing (e.g., loose, teabag)
• brewing time
• which infusion it is
- Amount consumed
Boros, K., et al., “Theanine and caffeine content of infusions prepared from commercial tea samples,” Pharmacognosy Magazine 12(45):75–79. Jan–Mar 2016.