Just how much caffeine is in a cup of tea anyhow?
Asking that question is a bit like asking “how many dogs will fit in a car?” The answer of course, is, “It depends”.
How big is your cup?
Generally speaking a “cup” of tea is about 6-8 ounces. For most teas, it is recommended to steep about 1 heaping teaspoon per “cup” of tea. But some people might like their tea weaker or stronger, and some of us drink our tea from a 20 ounce mug (the better to warm both hands on a cold winter morning).
Which style of tea are we talking about?
The longer the tea is oxidized during fermenting, the more caffeine it will contain. So, white tea contains the smallest amount of caffeine, and black has the most, in theory.
How strong do you drink your tea?
Fewer tea leaves means less caffeine, and more tea leaves means more caffeine. If you like a cup of tea that you can stand your spoon up in, it's going to have more caffeine than the infusion that you can read the newspaper through.
*interesting fact: The leaves of the tea plant contain more caffeine than coffee beans, but since coffee is usually made as a much stronger infusion than tea, a cup of tea will have less caffeine.
Time and temperature play a role too.
The hotter the steeping water, the more caffeine is extracted. Since black teas are infused at higher temperatures, and for a longer amount of time than green, oolong or white teas, more caffeine will be released into the cup. On top of that, white, green and oolong teas are often re-infused several times, and each subsequent infusion will contain less caffeine than the first.
Taking all of these factors into consideration, a cup of black tea is going to contain more caffeine (between 14 and 70 mg) than white, green (24-45mg) or oolong, but it will still be lower than a cup of coffee (95-200 mg).
What about Decaf?
Decaffeinated tea is available, but as with decaffeinated coffee, there is a price to pay. There will be some flavor loss in the decaffeination process, regardless of whether ethyl acetate or carbon dioxide is used. I perceive it as a loss of “bite”, similar to a caffeine-free cola.
The amount of caffeine in a cup of tea can be reduced at home by steeping the tea for 30-60 seconds, pouring off the steeping water, adding freshly boiled water, and steeping again for the usual amount of time. There will be flavor loss with this method as well, so it's not ideal to try this with flavored teas.
If caffeine consumption is of concern to you, it might be best to stick with the white or green teas, and the lower water temperatures and shorter steeping times that are recommended for them. Or, if those aren't your cup of tea, consider Rooibos, herb & fruit tisanes, or herbal tisanes. Nearly all of these, with the notable exception of Yerba Mate, are naturally caffeine-free.
Want to learn more?
For a breakdown of the caffeine content of tea and coffee, see this article from the Mayo Clinic: www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20049372