I have seen a lot of instruction where ratios are given rather than volume. Makes sense to use weight since crema can be thick or thin. I understand the principle, what I don't understand is that this information is not enough.

I assume that water weighs more than dissolved solids from the coffee, makes sense since water is very heavy. I don't have a scale, actually I do not have an espresso machine at the moment, so I can't test this myself. Lets say one makes an amazing shot of espresso, lets say starting off with 18 grams and ending with 36 grams. Would the 'volume' be the same as 36 grams of just water if one compared the volumes of that great shot of espresso with the 36 grams of water?

Confusing thing to me is that ratio is only one part of a very complicated art with many variables. With dripping water one will get to a ratio of 2 to 1 if that is the ratio one chooses, but it could just be a watery shot.

Ken

First off, you're right, ratio is only part of a good recipe. It's a lot easier to measure than using a $400-1000 refractometer or carefully dehydrating your espresso and pucks and using a very sensitive scale.

The assumption with "ratio" is that your coffee, grind, flow rate, pressure, temperature, and all result in an extraction that is considered "done" for the brewing method. Let's say that 20% extraction yield (EY) is reasonable for espresso. 18 g in the puck, 20% of that goes mainly into the cup, 3.6 g. For a 36 g shot, that would mean a bit over 32.4 g of water (in the cup, there will be quite a bit still in the damp puck).

Dissolved solids are the key there. Many times, you can dissolve a lot in water without significantly increasing the volume of the solution. As one example, dissolving common salt in water can decrease the volume by a couple percent. When in solution, the molecules can fit in between each other.

Thanks Jeff for your help, here and in my other threads!! Really appreciate it!

Makes sense that everything else needs to be perfect.

Ken

You precisely understand why you should get a scale. Even the cheap $10 ones on Amazon which I still use to weigh beans have worked for me for years, and they're very accurate per calibration test weights.

EDIT: Oops, they're not $10 anymore. More like $15-16. I've got them in my kitchen, motorhome, and roaster ... and had one at work too, and none have ever failed me.(knock wood)