Liquid Retained Ratios (LRR)
The name for the coffee that doesn’t manage to drip out of a pour-over, or the bit of coffee we don’t manage to remove from a plunger when we are serving it, is the interstitial liquid. It is stronger in a plunger than it is in a pour-over and usually there is more of it in a plunger.
The normal amount of liquid you will lose to your grinds with immersion brewing, where the service style involves the liquid being decanted off the grinds, such as the jug method, plunger or cezve coffee, is approximately 3ml per gram of coffee. The normal LRR for a drip coffee is around 2ml per gram. The term for this relationship between your dose and the amount of water it traps at the end of a brew is the liquid retained ratio (LRR).
LRR for Immersion
For immersion brewing, we have less of a problem when trying to calculate the overall extraction yield. We can assume that the interstitial liquid was just as good to drink and exactly the same strength as the coffee that made it to our cups, so we consider the beverage weight to be the entire amount of liquid. Most people will then say this total liquid equals the total amount of water, but if you really want an accurate reading, you should consider that you have caused some of the coffee to dissolve into that liquid, too, so it’s heavier than it was to start. Here is an equation to help you work that out which Andy Schecter helped BH put together.
Brew Water Weight
________________ = Immersion Beverage Weight
In order to precisely calculate extraction in a cupping bowl, you can recalculate the beverage weight using the Schecter Conversion. Let’s say, for example, you use 180g of water to prepare a cupping bowl, a 10g dose of coffee and you measure a TDS of 1.2%.