# Is the reduction of caffeine in a second cup of coffee linear or other?

I use my Keurig coffee maker each morning. Most often, I drink two cups of coffee, but I use the **same** K-cup for both; the second cup is just a little more watery.

I assume that the in the first cup, I am getting a larger percentage of available caffeine than in subsequent cups, since the coffee hasn’t been diluted yet.

Here’s the question: When I make the second cup (or theoretically a third) is the reduction of caffeine content linear? Or does it follow some other factor? Is caffeine reduction predictable?

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## 15 Answers

I don’t know how they measure caffeine in coffee but believe it might be predictable.

Then again,it probably varies by the kind of coffee. Even if you are using the same kind, maybe caffeine amounts vary by batch. Would the conditions such as weather & time under which the beans are harvested make a difference even within the same type of coffee?

For now, you will just have to go by taste or effect. Maybe only have the third and forth cup and see if you are just as perky.:)

When you only have two data points, (Cup 1 and Cup 2)the function is linear, no matter what the process.

@zenvelo thank you for stating the obvious. What about the 3rd and 4th cups?

No the third point would the origin at zero coffee, zero caffeine, and I doubt that line would be linear.

My husband uses the same grounds for a large mug of coffee. He runs the Keurig twice right off the bat. I think he makes 14 ounces.

That doesn’t answer your question. Also, if you like piping hot coffee I guess it’s preferable to make a separate cup after you finish the first.

I, too, run it though 2 times, or 3. There are 3 settings on my Keurig: 6 oz, 8 oz and 10 oz.

My first will be 10 oz. The next will be 8 or 10 oz.

I will make a semi educated guess.

Since caffeine is highly soluble in hot water, 66 grams per 100 ml, I figure almost all, if not all, of the caffeine is washed out at the end of the first mug. The second or third are nearly caffeine free.

@JLeslie That’s the way I do it, run two cups from the same pod, and reduce the size of serving.

@elbanditoroso Here’s the question: When I make the second cup (or theoretically a third) is the reduction of caffeine content linear? Or does it follow some other factor? Is caffeine reduction predictable?

The Keurig’s probability density function is renowned for having a well behaved mean and variance but being highly skewed to the right with a platykurtic right tail. You may need to use a logarhythmic transformation to approximate the normal distribution.

Diuretic studies have concluded that second and subsequent cups are just a little more watery.

A typical cup of coffee has between 100mg and 200mg of caffeine. (0.1 gram – 0.2 gram).

Assuming a 10 oz mug,that is 300 ml of water.

The solubility of caffeine in water is 66 grams per 100 ml in hot water, So, 300 ml of water from the Keurig can dissolve 200 grams of caffeine.

The 0.1 – 0.2 grams are all washed out in the first mug. The second and later mugs have nothing.

That’s my guess and I’m sticking to it.

Ok, so this is very interesting to me now. If @LuckyGuy is correct, If I make a coffee after my husband, it’s basically a decaf cup of coffee, or very low caffeine. That’s good to know.

thanks, @LuckyGuy – most informative. What this tells me is that I can have a second or third cup from the same K-cup, and won’t be getting additional caffeine, so I won’t feel more jumpy later in the morning.

Most useful.

I do it like @YARNLADY does it. I take a large mug and I will do the largest brew size offered, and then into the same mug I will do the smallest (6 oz?) so I have about 16 to 18 oz in my mug from one K-cup.

@elbanditoroso Glad to help. That’s how I look at it.

@JLeslie Are you able to tell if coffee is caffeinated? If you can see a difference, please let us know your results. That would be good data.

I would expect it to be logorithmic/exponential assuming some percentage of the available caffeine is pulled each time and there is less available each subsequent pull.

Let’s guess the percentage is 80%.

First time you’ll get 80% of original amount of caffeine available.

Second time you’ll get 80% of the 20% that’s left… = 16%

Third time will be 80% of 20% of 20% ... = 3.2%

etc

Probably that’s not correct due to some caffeine being less available to the water, farther from the surface of the ground coffee than the original stuff. This would mean the first pull has even more than the later ones since it will get the easy stuff.

@LuckyGuy I’m not a coffee drinker. I have coffee maybe 4 times a year. I notice my caffeine intake 24 hours later when I feel a little crappy as I withdraw. It’s mild though. I recognize what the likely reason is, because I know I cheated and had caffeine for a few days then stopped. So, I don’t think I’ll be able to gauge it. I do feel really good when I drink caffeine, but I’m not extremely amped up or jittery or anything like that. I can feel good anyway.

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