I wanted to follow up on the previous post before the end of the month, so I went ahead and ran the extractions yesterday evening. The results were just about what one would expect, with one difference: agitation did not have an appreciable effect on caffeine extraction. An additional concern was the efficiency of the extraction, so I added an additional sample to as a pseudo-standard, namely standard brewed coffee from the office Mr.Coffee machine. With this I was able to determine that the extraction was roughly 33% complete, but there is some margin of error there.
24 hour with agitation (#1) | 24 hour still (#2) | Office coffee (#3) | Diet Coke* | |
Crude Caffeine Isolated (mg) | 14.30 | 16.74 | 3.10 | - |
Total Caffeine (mg/cup) | 451 | 550 | 100 | 29 |
* Literature value via the Mayo Clinic. Chosen due to how frequently my friends consume it.
The second interesting result was simply how much stronger the toddy (24 hour cold brew) was compared to standard hot drip coffee and soda; more than 5 times as much caffeine as the office brew, and 19 times as much as a cup of diet coke. To be fair, people typically drink coffee in smaller volumes. I worry that these numbers may be too high, as I'm not sure what share of the measured mass is impurities. If the numbers are close, that'd solve the riddle of why I've been so susceptible to caffeine headaches when I miss my morning coffee, I used to drink almost a cup of toddy a day.
I want to emphasize that I am not a chemist, I've not been trained as such, and having a background in materials science is not "pretty much the same thing". As such the experimental procedure was just as interesting to me as the result. I will not reproduce all the details here, as there are many many write-ups for this exact extraction out there. Several of the more frustrating bits I will, however, elaborate on. Namely the problem of emulsions. If you've ever seen oil and water, you know they separate into layers, but if you shake it enough you'll get a layer made of bubbles of one in the other that persists; That's the emulsion. Through the three trials I tried a number of methods for getting rid of the emulsion after agitating the coffee with dichloromethane.
As I couldn't get my hands on a sepratory funnel, I ended up using a column with a loose glass top stopper. This prevented me from mixing the liquids by simply inverting it slowly, so instead I swirled it such that the liquid at the top got pulled to the bottom and vice versa. This produced varying levels of emulsion across the three samples.
I tried stirring with a glass rod, and that helped some. A write up I found online suggested sonicating, which only served to worsen the problem. Waiting produced the most consistent improvement. The clear answer was to decant the whole mess and centrifuge it, but due to time constraints I opted to stop decanting right at the emulsion's edge (hence the 33% extraction, which should have been much better). The final result contained at least some contaminants, as caffeine ought to be a white solid and what was yielded was yellow to brownish red.
The take-away from this experiment is two-fold: agitation has no significant effect on the extraction of cold-brewed coffee, and cold-brewed coffee is ridiculously strong even given a large margin of error. Were I to repeat these experiments again I would filter after the introducing the calcium carbonate rather than allowing it to settle and pipetting off the top, and I would agitate in a sealed container (venting occasionally) and centrifuge the result to sidestep the whole emulsion issue. I've read that a sublimation purification can also reduce the apparent color, but some of the results I've seen are not promising.