Increase cold brew coffee concentration

Question

I like the taste of cold brew coffee but I prefer to drink it hot. A certain proportion in which I dilute the concentrate with boiling water gives me the best taste, but the temperature of drink gets too low (even when the concentrate is at room temperature, I imagine it will be even lower if the concentrate is refrigerated).

My concentrate is brewed in proportion 1:4 (coffee to water by mass). That's the highest concentration most recipes suggest. I also tried using finer grinds and increasing the extraction time (up to 30 hours).

One way to solve the problem would be to try proportions 1:3 and 1:2, but would I be wasting too much coffee this way?

Another way would be to heat the drink, but that's inconvenient in office.

I could try boiling down the concentrate, but I'm afraid this will affect the flavor.

Does anyone have other suggestions?

Answer 1

You should reduce your coffee concentrate by placing it in a vacuum to lower the boiling point of the water down to room temperature. Lowering the pressure of water decreases its boiling point. This way you will boil off the water quickly without adding heat and risking any changes in flavor.

Otherwise you can put your coffee concentrate in an oven on a low heat setting poured into a glass or ceramic baking pan to maximize the surface area. Use the convection setting if you have it. The added heat shouldn't cause too much of a flavor change since the coffee beans have been removed at this point and won't continue to brew/extract harsh flavors.