1.2 spots of tea June 19, 2013Posted by mareserinitatis in food/cooking, physics.
Tags: caffeine, diffusion, tea
(Yes, folks, it’s a caffeine molecule. Take note as this is one of the few chemistry-centric articles I will ever post.)
In the past few months, I started re-exploring my interest in tea. It’s been a lot of fun trying different varieties of teas and learning what things I like (malty) and what I don’t (green).
Recently, however, I began having issues with insomnia, and I discovered it wasn’t wholly unrelated to my interest in tea. I’ve found I have to be very careful how I brew the stuff lest I overdo it. Specifically, the problem occurred when I went from brewing my standard amount of tea in 8 oz. batches for a total of 16 oz. to just brewing 16 oz. all at once using twice the tea. It may not sound like this should make a difference, but it does.
When I went to search for answers, one of the papers that kept popping up was Tea preparation and its influence on methylxanthine concentration. Methylxanthines are compounds that have been shown to potentially have ill effects on health and, sadly, caffeine is included in this group. The paper outlines a study where they brewed tea for five minutes and then checked the caffeine content (among other things) using HPLC (high performance liquid chromatography). They went further than that, however, and also resteeped the teas a couple more times. They came to the conclusion that it took about 15 minutes of brewing to extract all of the caffeine from the tea leaves. The blog Cha Dao has a nice extrapolation of these results into one-minute intervals. (I’m not sure how the extrapolation was done, but it’s reasonable to assume a linear curve fit.) The post also includes results from another study that involved brewing the tea using a magnetic stirrer. I’m not particularly fond of the results, however, because most tea is brewed using only diffusion and the stirrer introduces convection into the mix, which isn’t quite as realistic (though likely more repeatable in a lab setting).
The extrapolation looked like this:
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
Let’s look at an example and then it’ll become clear why my tea consumption was causing me some problems. Being a physicist, you know I absolutely am dependent on using some sort of variable, so I’ll assume that x is the amount of caffeine in one teaspoon of some of the very delicious Keemun Mao Feng that I’ve been drinking the past few days. According to the chart at Cha Dao, if I brew my first 8 oz. for three minutes using one tsp. of tea leaves, that should remove half the caffeine from the tea leaves and put it into my drink. If I take another 8 oz and resteep the tea leaves for three more minutes, we can see that it should extract half of the remaining caffeine from the tea leaves, giving the second 8 oz. a caffeine content of x/4. I then put all the brewed tea together in my thermos, which conveniently holds 16 oz., and the total amount of caffeine in my morning tea should be 3x/4. (I did do a mental check on this method and pretended I steeped 1 tsp. of tea for 6 minutes, and the percentage of caffeine removed from the leaves into my drink was about the same.)
Now let’s look at the other method. If I choose to use twice as much tea and steep it all at once in 16 oz. of water for four minutes (which is what I had been doing when the sleeping problem creeped up), this means my initial caffeine concentration is 2x. According to the chart, steeping it for four minutes will take 60% of the caffeine from the leaves and put it into the drink. My total caffeine content of my drink is then .6(2x) = 1.2x. This is 60% more caffeine than I was drinking when brewing it the other way. As I am apparently rather sensitive to the amount of caffeine in my drinks, this ended up being a BAD idea. However, now that I know why I was lacking sleep, I’ve gone back to my original brewing method despite it taking slightly longer.
Beyond that problem, I have also had issues when switching tea types. I think the solution is to label each type with the amount of caffeine…preferably in terms of x.