You may have heard that black tea has more caffeine than green tea. You may have heard the exact opposite- that actually, green tea has more caffeine than black tea. In reality, you can't say that all green teas have more caffeine than black teas (or the reverse). The question of how much caffeine is in your tea is a combination of the type of tea, how it was processed, and how it's prepared.
1. OXIDATION
Teas that are heavily oxidized have less caffeine than a lightly oxidized tea. This means that white and green teas contain more caffeine than black tea. However, the way the tea is processed and how it's brewed will change the amount of caffeine that is released during brewing (AKA the tea you are actually consuming).
2. WHOLE VS TORN LEAVES
Teas that are ground or torn up (like certain bagged teas) are higher in caffeine than whole leaf teas. This is because the caffeine is released more quickly when the leaf is damaged as opposed to when it is intact. Some black teas are processed using the CTC (crush, tear, curl) method and the infusions from these teas will have a higher level of caffeine than a whole leaf green tea infusion, even though green teas have higher caffeine content than black teas.
3. STEEP TIME AND TEMPERATURE
By a similar logic, teas that are steeped for longer and at higher temperatures have larger amounts of caffeine than ones that are steeped for a shorter period of time at lower temperatures. Again, because black teas tend to be steeped for longer than green teas at a high temperature, the infusion may end up having more caffeine than the green tea.
Overall, it's tricky figuring out exactly how much caffeine you're consuming when you enjoy a cup of tea but these tips can also give you an idea of how to manipulate your brewing technique to get more or less caffeine. Overall, take into consideration these factors and listen to your body as that is the best gauge!