Coffee Soluability/Concentration I need to know: 5 pounds ground coffee soaked in 3.5 gallons of water for 18 hours, unheated. Resulting coffee liquid extracted is x. 
How do I cut in half the water amount but still get the same amount of extracted coffee soluables into 1.75 gallons of water as would be in original 3.5 gallons?Can't allow reducing water amount by heat evaporation.
Thanks in advance,
AJR
If this what you are looking for?  https://en.wikipedia.org/wiki/Coffee_extraction

There are a couple of graphs in there to help you get your ratio right (and I assume you will need to experiment on your side).

IMO, heating the coffee solution to evaporate the water will result in the degradation of the coffee; maybe render it overly bitter.