The other night, a friend of my husband’s was visiting. I remembered that on a previous visit, this friend had recognized my husband’s gaiwan for what it was and asked why he was using it as an ashtray. I explained that we found it at a thrift store and it didn’t have a lid, making it useless for tea; a point he conceded. So I mentioned to him that if he wanted I could make a pot of tea for him. He demurred, stating that he can’t have tea past noon because of the caffeine. I nodded knowingly, and admitted that I can’t have caffeine after 5pm, myself.
This exchange brought to mind a discussion that I had previously with my husband where he had been of the belief that my cup of morning tea had as much caffeine as his morning coffee. While it was a simple matter to find the amounts of caffeine in coffee and tea respectively, it started me researching the caffeine content in tea and the many factors that can affect it; something that I’ve gone back to periodically as a continuing curiosity.
In Michelle’s article Decaf Tea – Au Naturel, she mentioned the lack of data regarding caffeine content of different types of tea and the fact that none of us steep green tea in boiling water. She asserted that this renders any scientific results regarding the caffeine content of different teas effectively useless because they all use boiling water as part of the study. While I couldn’t find any studies involving multiple tea types at multiple temperatures (most of the studies compared only two types of tea in cross-temperature experiments), I did find some fascinating information. Some of what I found seems obvious, but some other data surprised me. Here is a short summarized list of some of the more interesting facts I came across from different studies.
Basic Facts
- Water temperature has an effect on how much caffeine will be in the infusion.
- Steeping time of loose tea has an effect on how much caffeine will be in the infusion.
- Caffeine quantity of loose tea decreases with each steeping; however, this levels off and becomes constant at the fifteen-minute mark.
- By the time tea has steeped for a long enough duration to have very little caffeine, it would also have no catechins, antioxidants, or any of the other beneficial ingredients of tea. (Or, presumably, flavor!)
- Loose tea still had noticeable flavor during the second and third infusions. Caffeine contributes to tea flavor, as do numerous other compounds.
- The caffeine content is influenced by the plant varietal, growing environment, and manufacturing processes.
From “Factors Affecting the Caffeine and Polyphenol Contents of Black and Green Tea Infusions”
More information and conclusion tomorrow!
Sources
Caffeine in Chiang Rai tea infusions: Effects of tea variety, type, leaf form, and infusion conditions
Tea preparation and its influence on methylxanthine concentration
Factors Affecting the Caffeine and Polyphenol Contents of Black and Green Tea Infusions
Caffeine in teas: levels, transference to infusion and estimated intake
Photo “Project 365, Day 78: Tubes of Teas” is copyright under Creative Commons Attribution-NonCommercial Generic License 2.0 to the photographer Mark Atwood and is being posted unaltered (source)
Any new information on caffeine in tea is greatly appreciated. I look forward to Part 2. Thanks for doing the heavy liftying!
Certainly! Your post was part of what prompted me to go ahead and write about it, so I’m glad to be able to help. I’m also more than happy to put in the time for research, I kind of enjoy it.
Nice to see an article on caffeine. Nigel Melican has done studies that show that all the caffeine is not steeped out until 15 minutes pass.
This is a subject we’re really into and did a video on caffeine in tea here: http://bit.ly/2N0knuY
Yes, but that’s with boiling water! We need some hard facts on caffeine with green and white tea along with Japanese senchas which also have a lower temp and time for steeping.
Looking forward to seeing that. You might want to Google Nigel Melican, caffeine in green tea and see what happens.
Diane,
It’s interesting that you found that the caffeine is all steeped out after 15 minutes. The first of the studies I linked (“Caffeine in Chiang Rai tea infusions”) said that after fifteen minutes it still released a small amount of caffeine, though the quantity had stabilized. “For the period of 0.5–15 min, the concentration of caffeine increased rapidly whereas, for the longer infusion time (15–60 min), the caffeine concentration increased only slightly.”
Interesting! Here are Nigel’s findings: http://bit.ly/2tlqBit
The studies done by Camellia Sinensis, and published in their books, use differing temperatures for different teas – for example, 65C for a gyokuro, 75C for a sencha, 80C for a bai mu dan, etc. The information they’ve published is quite detailed.
Thank you Ken. Any way to get the information short of getting the book?
This came in from Ken – Not that I know of. I’ve only seen it in their books – primarily in Tea – History, Terroirs, Varieties. I don’t see anything on the studies on their website.
I do appreciate you checking.