DamianWarS wrote:Immersion
EY% = TDS x total water weight / dry coffee weight

Not quite.

EY% = (TDS / (1 - TDS)) * total water / dry coffee

just to quibble it further, I think if you are talking EY% (extraction yield percent) and using TDS%, the equation would need to be:

EY% = TDS% / (100 - TDS%) * total water mass / dry coffee mass

This is the same as using fractional values instead of percentages (ie, a TDS of 1.5% would be 0.015)
EY = TDS / (1-TDS) * total water mass /dry coffee mass

Note that if you use DamienWarS' simple equation it doesn't make that much difference, maybe a few tenths of a percent overestimated * underestimated EY%.

* Edit: corrected above (see post below)

homeburrero wrote:Note that if you use DamienWarS' simple equation it doesn't make that much difference, maybe a few tenths of a percent overestimated EY%.

Underestimated.

If the water/coffee ratio is 15:1 and DamienWarS' formula says 20.0% it would really be 20.3%. And if the ratio were 8:1 it would be 20.5%. Like so many things with using the concept of extraction it's all very fuzzy anyway and makes the most sense when comparing apples to apples.

jpender wrote:Not quite.

EY% = (TDS / (1 - TDS)) * total water / dry coffee

you're right there's better ways of doing it, I kept it simple (meaning I didn't want to think too hard) to demonstrate the point of how to justify the ratio drop from 1:15 to 1:13. Indecently Rao uses the same EY formula in his blog that I referenced (probably also to keep it simple). He also has a parenthetical that for immersion you should factor in the weight of the dissolved solids into the water weight as well. so if the TDS is 1.5 and the water weight is 100g, then the total should be 101.5g

DamianWarS wrote:...Rao uses the same EY formula in his blog that I referenced (probably also to keep it simple). He also has a parenthetical that for immersion you should factor in the weight of the dissolved solids into the water weight as well.

That's what the 1/(1-%TDS) factor is about, including the mass of dissolved solids. That's how you measure the concentration of a solution: the solute divided by the solution, not the solute divided by solvent. With percolation brewing you measure the beverage mass so you're already including the dissolved solids.

Did Rao write it that way to make it simple? He included it as part of an argument for making the definition of extraction a lot more complicated. Why would he tack on dubious minor adjustments without starting with an accurate version of the more generally accepted definition? It's not as if that extra factor is mathematically complex. I think that either Rao was being sloppy or he just made a mistake. Jonathan Gagné has a proposed a similar idea about incorporating the dissolved solids in the grounds in percolation brews and he managed to get the math right. It's really not that hard.

It's me that's being sloppy, although broadly it's the same point I should have been more clear that it was simplified (I've added a disclaimer to the post I made) to Rao's credit he does clarify. But I appreciate being challenged on it because accuracy is important for anyone involved.

DamianWarS wrote:with percolation it's different. clean water is constantly poured over a bed of coffee, washing away coffee solubles and then repeating it with more clean water.

Isn't it true that in a percolator coffee maker (like the old...but still sold stovetop models) it is not "clean water" that is constantly poured over the coffee bed but rather the brewed coffee that has previously been extracted...and will continue to be cycled back through the grounds in the filter basket as long as heat is applied to the water reservoir? I suppose that some percolators turn off automatically after a set time, but even in those the only clean water poured over the coffee bed is during startup. Or am I missing something?

Pressino wrote:Isn't it true that in a percolator coffee maker (like the old...but still sold stovetop models) it is not "clean water" that is constantly poured over the coffee bed but rather the brewed coffee that has previously been extracted...and will continue to be cycled back through the grounds in the filter basket as long as heat is applied to the water reservoir?

Yes, that's right. Percolators are a lot more like a well agitated presspot than a pour over. But DamianWarS wasn't talking about percolators. He was talking about percolation.

Pressino wrote:Isn't it true that in a percolator coffee maker (like the old...but still sold stovetop models) it is not "clean water" that is constantly poured over the coffee bed but rather the brewed coffee that has previously been extracted...and will continue to be cycled back through the grounds in the filter basket as long as heat is applied to the water reservoir? I suppose that some percolators turn off automatically after a set time, but even in those the only clean water poured over the coffee bed is during startup. Or am I missing something?

in a percolator, the first cycle is of course clean water but after that, it recirculates the brewed liquid into the coffee bed getting stronger and stronger, and eventually should reach an equilibrium like what happens in infusion or with immersion brewers. with percolation, a constant source of clean water washes away the coffee solubles but that's not happening with a percolator. with a percolator, the brew will probably be closer to immersion than percolation despite its name.

OK, thanks for that clarification. What you are describing sounds more like the old Silex or "Kona" coffee maker. We had one at home when I was a kid, and I preferred the coffee that came from that rather than from our metal stove-top percolator...though I did like the sound and smell it made while brewing...which was used along with video of coffee splashing in the glass percolator top in an old Maxwell House coffee commercial...