There are over 3,000 types of tea and most has not been tested for caffeine content, so there is a 'general rule' for each tea type, which may or may not be accurate.
Experts argue that caffeine is what makes tea taste like, well, tea. Their suggestion is to choose an herbal or rooibos if you don’t want caffeine. Caffeine binds with polyphenols during the steeping process and allows for a gentler ‘caffeine buzz’ than coffee. Doses of less than 300mg/day of caffeine have generally not been associated with health risks, but consult your doctor.
Actual caffeine level in tea is highest:
Gascoyne, Marchand, et. al. in their book 'The Terroir of Tea' completed a study comparing a select number of assorted teas for their caffeine content. No surprise that matcha had the highest content. However, what they did find was that contrary to popular opinion, many greens had a higher caffeine content than some blacks. In the study all teas used 5g of leaves with the exception of matcha. Interestingly, yerba mate, which is often touted to have 70mg of caffeine, had only 18mg in their study. In reality, the traditional way of drinking yerba mate in South America is to put approximately one ounce of mate into a gourd, which would significantly increase the caffeine level; yet mate would have less than most teas if only a heaping teaspoon of mate was infused.
Debunking the 30 second ‘quick steep’ myth:
There are no scientific experiments that correctly document the release of caffeine in all types of tea over a specific time, using the correct water temperature. Hicks et.al. maintain that only 9% of caffeine is removed after 30 seconds, but the water temperature was boiling for all teas, which would not be applicable for green or white teas, in my opinion. If the black teas used the CTC manufacturing method to produce tea pellets (for tea bags) – which are specifically designed for rapid extraction of color, flavor and by definition caffeine; it may be possible that a significant amount of caffeine could be extracted in 30 seconds.
The 30 second ‘quick steep’ to decaffeinate may be a myth, but then again, it may not be for some types of tea. The Chinese do a very quick rinse of their leaves, calling it 'awakening of the leaf' so the next steep is more flavorful. If caffeine is also discarded, then there is a twofold benefit. Just exactly how much caffeine is discarded is the real question.
Decaffeination has a legal definition: 97% of the caffeine that was present before processing must no longer be present following processing.
Hicks, et. al study using 212° water temperature:
30 seconds: 9% caffeine removal
1 minute: 18% caffeine removal
2 minutes: 34% caffeine removal
3 minutes: 48% caffeine removal
4 minutes: 60% caffeine removal
5 minutes: 69% caffeine removal
10 minutes: 92% caffeine removal
15 minutes: 100% caffeine removal
Spiro in his study found 20% removal at 30 seconds. But both a far cry from the 80% that is often postulated.
Experts do seem to agree that there is less caffeine in tea than coffee..............
Nigel Melican; ‘CAFFEINE AND TEA: Myth and Reality’
1996 'Tea preparation and its influence on methylxanthine concentration,' Hicks, Hsieh, Bell
Spiro, “Tea and the rate of its infusion” Chemistry in New Zealand, 1981Caffeine: