I won’t start the cold extraction experiments until I finish the response surface set, and possibly until I perform some local optimization using the RSO outcome. To warm up, paradoxically, here are some thoughts on cold extraction.
The basic process, everywhere I’ve read about it, is to put grounds in room temperature water for a long time—overnight for example—and then filter or decant the extract into storage. The extract is generally much stronger than regular coffee, and so to serve it you dilute it with hot water.
Naturally, you can buy expensive equipment to help this process, or you can use a French press. I imagine that decanting through your drip pot’s filter cage would work well too.
The premier advocate of the method would appear to be Toddy Products. They recommend extracting one pound of beans in 9 cups water, then reconstituting the coffee with 3:1 hot water to coffee extract. I’m guessing that you get about 8 cups of extract, and in turn 32 cups of coffee. I believe that Toddy is talking about 8 fl oz cups, though in the world of coffee you can never be certain. In any case, 1 lb of coffee to about 32 cups of water corresponds to a C/W ratio of 0.060 g/ml. This compares quite reasonably with the C/W ratio used in hot brewing. Recall that in my experimental set-up I use ratios between 0.035 and 0.075 g/ml.
Another site recommends using 1 gallon (16 cups) of water with 1 lb of coffee. All the other sites I examined suggest similar ratios of approximately 0.060 g/ml.
Recommended grind size is coarse, though it appears the reason is to allow easy filtering. Since extraction time is 6 to 12 hours, depending on reference, I suspect that what dominates the extraction process is the solubility of various compounds at room temperature, rather than the diffusion of those chemicals from the beans. Any old grinder is probably fine, and variation in the particle size is probably irrelevant.
I believe this process will make an insipid cup of coffee. It is recommended by some because it produced lower acidity and less bitterness. Translation: less flavor. Terroir Coffee asserts that the “resulting cup is light bodied and bland since all acidity and many aromatics, which require hot water for the right chemical reactions, are never formed.” Not inspiring. Of course, I didn’t think brewing coffee had much to do with chemical reactions as with dissolution…
The process offers great convenience in that you can brew just once for two weeks’ coffee. Furthermore, it should be palatable to people who like weak coffee. The strength of the cup can be easily changed to suit the members of your party.