Does a K-cup deliver the same amount of caffeine regardless of cup size?

You will get more caffeine in the larger size obviously, it is more coffee. The first 6 ounces is the same no matter which size, and then add on the additional ounces. The last 4 ounces might be a little weaker, but still pack in some caffeine.

I would think it would be less caffeine in the larger cup. If you think of a tea bag and put it in a cup with more water, the tea, and thus the caffeine in it, will be more diluted and weaker. So I would think the same principle would apply with the K-cup.

The Keurig is one pod that the OP is running 6 ounces or 10 ounces of water through it if I understand correctly. The first 6 ounces are exactly the same. The first 6 ounces are not more diluted in the 10 ounce cup. The additional 4 might be slightly less, but likely not, because the keurig is made for 6 or 10.

Even the tea bag example I think the ten ounces is more caffeine, because unless you leave the tea bag in exactly the same amount of time for the 6 and 10 ounce, the tea bag has plenty of tea in it to make a dark cup of 6 or 10 ounce tea.

Maybe if it is the same tea bag or keurig cup for all 18 or 30 ounces there is more difference in caffeine, because the beverages start getting really light after 18 ounces, but even then still more caffeine is being added, although maybe marginal.

Well yes, it would have to be the same amount of time steeping.

No, you’re running more water through with a larger cup, and that’s more water in contact with coffee over a longer period of time. You’ll get more caffeine with the largest size. It falls off on a curve, but you’re undoubtedly getting more.

What matters most is the steep time. Longer steep, more caffeine. Same principal as making Tea except most coffee makers do not allow you to control steep time.
I doubt a K-cup style machine allow that control.
French Press is the best for this control and very reasonably priced.

I believe LuckyGuy did a test about this a few years ago. I’ll send this q to him and see if he responds.

It’s diminishing returns. You get the most caffeine from the first ounce through the K-cup, less from the second oz, and by the 40th ounce you’re probably not getting much of anything (though l would guess a lab could find detectable amounts).

Making an estimate here… The first 6 ounces, 180 ml, will dissolve 90% of the caffeine in that pod. Running it through a second time will yield almost no additional caffeine

The solubility of caffeine in hot, 100C, water is 66 grams per 100 ml or 132 grams in 200 ml.
The amount of caffeine in a K cup is about 100mg or 0.1 gram. (about 1/1000 of the solubility limit)
That tiny amount goes into solution almost immediately when the first hot water washes through the pod.
You can try the experiment yourself with sugar. Sugar is about 8x more soluble than caffeine. Try putting 1 gram (10 times 0.10gram) of sugar.into a pod and running 6 oz of hot water through it. Taste the sugar? Yep. Now look in the pod. Any left ? Nope. Run another 6 oz through it. Taste any sugar. No to “Maybe”.

Use your pod to make the largest mug you can or use the pod twice. You are only getting 100mg caffeine total.

^^Oh interesting. So even if the 4 ounces (after the 6 ounces) still tastes very similar to the first 6 ounces, you are saying the caffeine content in the last 4 ounces would be very low. Is that correct?

So it sounds like I was right.

@LuckyGuy Thanks for the excellent explanation. I noticed similar results to your sugar experiment in “cocoa” K-cups. Once you run the hot water through it, it’s empty, unlike the coffee pods.

Although I use the machine for tea sometimes, I only use it for the hot water, allowing it to drip over the bag.

@janbb Of course!

@janbb Yes it does regarding the caffeine! :) But not exactly for the reasons you thought. Still, you were closer to the right answer.

@JLeslie I imagine the flavors and oils take longer to go into solution so the liquid is still brown after the second wash , or later 6 oz of a 12 oz mug. It just doesn’t have any caffeine in it.

@LuckyGuy I think this is something a lot of people would want to know.

@JLeslie2 I’m confident my answers are reasonably close. However, I am actually considering getting tests done to get real answers.
I’m thinking of a test where I set the Keurig to make a 12 ounce mug. Then I “clean catch” 2 ounce vials as it is running. That would give me 6 samples that could be run for caffeine and turbidity.
I’ll see how expensive it is.

In the meantime you can use my estimate: the second run through a k cup is decaf.

@LuckyGuy I would be very interested. I don’t drink coffee, but my husband does. He makes a ten ounce every morning. His Keurig it’s 5oz and another 5oz, but that’s a minor point.

I want to go back to @janbb’s tea example. I make light tea, the tea bag is in the water for much less than a minute, I could time it. So, am I to understand that my light tea probably has just as much caffeine as when someone steep’s the tea for two minutes?

Moreover, quantity of water doesn’t matter if I understand correctly. Assuming I am drinking the entire amount of tea that I make in one sitting. 10oz of tea or 20oz with one tea bag, if I drink all of it I get basically the same amount of caffeine whether I steep for 1 minute or 3 minutes.

Only lab tests will reveal what is going on, don’t be surprised if it’s not what we think. The initial rush of water will carry away the tiny particulates that fit through the filter as well as caffeine, and that will deliver a lot. What is different is the grounds are cold and the water is forced through rather than being steeped. I would think that it is entirely possible that there could be more caffeine in the last part of the process because the kcup has been full of hot water longer. I think the curve for Kcup sizes is flatter than we think. Surface area of the grounds, time it takes for caffeine to dissolve and how that changes with temperature matter. A drip coffee maker more or less takes those factors out of the equation.

^^Interesting hypothesis. So cool when what seems obvious is not in fact what is happening. This Q took so many unexpected turns.

I hope the caffeine testing isn’t expensive.

I found a high quality lab that can do this work. BUT, the test I outlined costs $1420.
They can perform only a 2 sample test for $453. EMSL Analytical
Another alternative is to buy equipment to do it. The Lighttells CA-700 analyzer costs about $2,500 and each test costs about $30 for single use reagents and sample tubes. The results will not be as accurate at the lab results nor be NIST traceable but they will be within a few percent.
Food for thought.

Wow. I’m shocked it’s so expensive.

Surely Green mountain coffee has already done this research.

So far everything I’ve found is for the full cup or pot. I did not see anything about partial fills .
There are many references for how much caffeine is in a cup. I used a base estimate of 100 mg. when I started thinking about solubility.

I was telling my husband about this Q and he pointed out that our K cups have much more coffee grounds than the prefilled disposable k-cups. We use the refillable and he fills it to the brim. Not sure if that matters.

Hard to say, single-use kcups use pressure also,the refillable just let the water run through.

I googled it and this link has a chart that has details which may help.

https://coffeeabout.com/k-cup-caffeine-content/

@jca2 Great article.

They did not offer any evidence, it appears to be someone’s wild ass guess.