Post By GrahamK
Post By Andy
Post By MrJack
Post By GrahamK
heard cutting shots short lowers caffeine content
I remember reading somewhere that most the caffeine in the coffee comes at the end of the shot and some people who drink a lot of coffee usually have ristrettos.
So incase I wasnt clear, 300mls of ristretto has less caffeine than 300mls worth of short blacks.
I have read on the net that with both coffee and tea, the longer it takes to be brewed, the more of the caffeine in the grounds or leaves gets into the cup.
At first blush this makes sense, the caffeine is embedded in the bean, so the longer you pass water through it, the more of the caffeine you'll extract.
I guess it might be different if the caffeine is easily extracted? So if 30mls of water is enough to extract 75% of the caffeine, then 60mls would have less caffeine.
I think water does not evenly travel through the grind in the basket, more dry away from the center.
Technically true, but you'd need measurements to tell if there was a significant difference or not.
Have a look around, I'm sure I saw some legit studies done on extraction rates.
According to "Espresso Coffee - The science of quality":
"Caffeine exhibits high solubility in hot water. nevertheless its quantitative extraction may be obtained only by coffee preparation methods that permit a long contact period between water and ground coffee. In espresso percolation, caffeine extraction yield is usually within the range 75-85%; this relatively low figure may be explained by the fact that caffeine is extracted from within the cell, by diffusion, and not by simple washout kinetics."
This may assist the discussion. To me it indicates that a ristretto may possibly yield less caffeine. No doubt including some Robusta in the blend may also have an effect on thew amount of caffeine extracted.
I would actually rate ~80% extraction to be rather high considering the speed of espresso extraction. There is no doubt a ristretto will have less caffeine, but the question is how much? If the volume is half, there still might be 2/3 the caffeine in there. Then again... a ristretto will contain a higher % of coffee oils compared to the remaining caffeinated water in a full shot. I don't think the 'within the cell' theory holds up unless you are brewing with intact green beans!
Although some factors will remain constant, the caffeine content will vary with your grinder, fineness of grinds, extraction time, machine, volume and blend. This all makes me wonder how popular coffee (and tea) would be if there wasn't any caffeine! Do we become addicted to the flavour partly because of the effects?
The comments were not "my theory", but from the 2nd edition of the book, (edited by Illy, Viani), and does state "usually" within the range. (The study reference given is Petracco, 1989). They also mention that the one substance that has been studied to a considerable extent is caffeine. So I would tend to go with their view.
Originally Posted by burr
Caffeine is extremely bitter, and has somewhat less solubility than the (usually) more desirable flavours in coffee. Ristrettos are less bitter than an full extraction.
So yes a ristretto would have less caffeine than a full extraction, although part of this is because there is less overall quantity of "result" in the cup. How significant this would be in equal quantities is something I don't know.
I drink ristrettos almost exclusively and rarely experience a caffeine overdose. Of course I don't drink 3+ ristrettos to give me the same coffee quantity as a standard double.
I have always regurgitated (unknown source, unlike GrahamK's Illy one) that "extraction of caffeine is directly proportional to the time in contact with water" and seat of the pants shows that:
caffeine = bitter
Percolated coffee and long brewed coffee = bitter
Same coffee as an espresso or a promptly pressed plunger = not so bitter.
The oddity to "my rule" is cold drip coffee and Dr Illy explains that with:
"Caffeine exhibits high solubility in hot water"
I'm pretty happy with that!
You may be right Andy,
I had a chat with my well read good buddy Dennis and he pointed out that long decaf shots are bitter too, so perhaps there is something else contributing.
His thoughts: Quinic acid...
I am not well read enough to dispute him!
Just to throw this out there, but I think it's unlikely to be a linear relationship between extraction time and amount extracted in espresso.
I would make a few assumptions that rate of mass transfer of caffeine from grinds to water is probably:
- proportional to how much caffeine remains in the puck
- proportional to the flowrate
So as you remove more of the caffeine, it may be extracted more slowly.
I would expect something like exponential decay.
That said, the reduction in resistance to flow following blonding may counteract the effect of reduced caffeine in the puck.
It depends quite a lot on many other factors (turbulence, temperature, adsorption energy, solubility), so I might be totally off track (plus, mass transfer wasn't my favourite subject area ).
In espresso, each mL of water is only in contact with the coffee for a short time. This means that in spite of the rapid mass transfer that comes with fast flow, there might not be enough contact time to saturate the water with caffeine.
In cold drip or slow percolation its a bit different. The caffeine will extract more slowly (unless you stir), but if you leave it long enough, the water will completely saturate will caffeine.
Solubility generally goes up with temperature, so the cold drip may extract less overall.
Heat transfer is an ok analogue. Put some ice in a colander and pour boiling water over it for a second. It will melt very quickly but will almost stop melting when the water stops. Put the same amount of ice in a pot of boiled water and it will melt more slowly but will eventually all melt.
I'm way out of my (chemical) depth here, but once again according to "The Book", Quinic Acid does contribute to bitterness. In addition the bitterness in Espresso, (due to its high viscosity & density), is actually masked by our sensory system due to the coffee coating our tongue (also contributes towards longer aftertaste). This apparently is why when diluting Espresso (e.g. extracting for too long etc), the coffee appears more bitter. And why other extraction methods also seem more bitter. I assume when diluted in milk, its a whole different ball game.
I however cannot find any credible references to cold brew coffee and caffeine, other than various web based hypothesis, and reckon your theory is as good as any of them Andy.
From the coffee research site.
Table 1. Compounds contributing to bitterness found in coffee.
My understanding, from all that I have read, agrees with the particle size/time/temp/caffeine yield premise.
I just stumbled across a link which suggests that caffeine extraction rate does decreases exponentally with volume. Can't speak to the reliability of the data, but the site seems well referenced generally.
Originally Posted by MrJack