Jofari wrote: You can imagine drip brewing as a series of smaller volume immersion brews (an infinite series in the case of a continuous pour). By adding fresh brew water throughout the brew, you are resetting the water concentration to zero and preserving the concentration difference between the water and coffee phase. Therefore, the extraction efficiency is better throughout the brew when compared to the more quickly decreasing extraction efficiency of an immersion brew.

Jofari, this made perfect sense to me until I read this article, by the barista behind "Sudden Coffee", by the way:

https://www.quora.com/What-effect-does- ... ds-content

In this article, the %TDS measured was identical in drip and immersion, while the former had 21% extraction and the latter about 24%. According to your explanation, I thought drip would have a higher %TDS and higher extraction%, which would justify having a larger brew ratio in VST tools to dilute the strength a little. I am somewhat confused now.

victorlinguist wrote:Does that mean that a 4 minute French press may lead to the same extraction yield as a 10-minute one? I am not sure I understood how extraction would halt. My gut tells me the longer you brew a French Press, the higher your chances of extracting bitter compounds, so I am a little confused right now. Thanks for your time!

My description of the process was assuming that only one compound is being extracted from the coffee. If that was the case, the overall extraction would halt after a certain amount of time. On a side note, I made a mistake in my earlier description. The equilibrium point, at which extraction will halt, is determined by the partition coefficient of the system (a ratio of solubilities between the two phases). The distance from this partition coefficient is what drives extraction and once it is reached extraction halts.

Things are complicated, however, by the fact that there are many many compounds being extracted from coffee. For each compound, the above will be true, but the partition coefficient and extraction rate will vary. This is why a 4 minute french press tastes different from a 10 minute one. By four minutes, some of the compounds will be finished extracting while others are still in the process.

victorlinguist wrote:n this article, the %TDS measured was identical in drip and immersion, while the former had 21% extraction and the latter about 24%. According to your explanation, I thought drip would have a higher %TDS and higher extraction%, which would justify having a larger brew ratio in VST tools to dilute the strength a little. I am somewhat confused now.

I should say that I have no experience measuring extraction with the VST refractometer and I'm not familiar with how it calculates things. The goal of my explanation was just to describe why drip brewing is a more efficient extraction process than immersion brewing.

I read the article and, like you, was initially surprised that a drip and immersion brew would have the same final concentration (TDS) at the same brew ratio. After thinking about it, I assume this is because other variable were not held constant for each brew, such as grind size and total brew time.

When it comes to calculating extraction yield from TDS, I agree with the author of the article and others who have posted on this thread. More of the extracted compounds are left behind in the brewing device in the case of immersion brewing than in drip. I hope this helps!

The ground coffee retains about twice its weight in liquid for both pour-over and for immersion, it's just the nature of the liquid retained that is at issue here. In an immersion brew, the ground coffee remains in the brew water until the end so the retained liquid will be full brew strength. In pour-over, you're continually washing the ground coffee with fresh brew water and washing the extracted coffee out of the grounds so by the end of the extraction, most of the extracted coffee will be washed out of the grounds and the retained liquid will be more dilute than the coffee produced so it makes less difference.

Some immersion methods like siphon may remove more of the water from the grounds since it pulls the water and air through the coffee bed at the draw-down resulting in less retained water.

victorlinguist wrote:In this article, the %TDS measured was identical in drip and immersion, while the former had 21% extraction and the latter about 24%.

There was no measurement. It was all imaginary in order to illustrate the difference between immersion and percolation extraction theory.

yakster wrote:The ground coffee retains about twice its weight in liquid for both pour-over and for immersion...

It depends.

With my Aeropress the grounds typically retain a little over one times the weight of the coffee dose. With my Brikka it is pretty much 1.0. With some French presses it would be considerably more than twice the weight.

What's the LRR for a typical espresso puck?