If I bring 20 ounces of water (2.5 cups) to boil in a kettle, and promptly remove it from the heat, is the amount of water lost (by volume/mass) a negligible quantity?
To be more precise about my own intent for this knowledge; if a pour over guide for coffee brewing is indicating that there should be twenty ounces of water at 195-205'f, should I go through the steps of weighing out twenty ounces of was-just-boiling water, or will the displacement of water to steam be relatively non-impacting of the coffee extraction and final cup.
What are the various ways in which more steam will be displaced, and how can I conserve mass to minimize variability and improve consistency extraction to extraction?
One of the prolific mods, rumtscho♦, came to answer with;
This depends on the time you need to bring it to boil (water evaporates long before it starts boiling), the surface area of the water, and your definition of "negligible". Best test it with your own kettle.
My kettle needed 2.5 minutes for boiling it, and lost 11 g out of 560, not quite half an ounce. It will probably lose some more while cooling. If you use an open kettle, a very wide kettle, or heat the kettle slowly, you will lose more.
This is good to know, and answered my question without saying it. A commenter below added the following, which made all the difference;
In rumtscho's measurement they lost about 2% of the volume - I expect based on the many factors involved this may vary from <1% to 5% or so. Even 5% water loss should not be enough to substantially affect the taste of the coffee unless your taste is very sensitive, but you can feel free to add 2% if you want to get a bit closer to the target (so 20.4 oz). – Derrick Coetzee
Insofar as I am not brewing coffee with lasers or thermal spectrometers, I'm a glad to know that this is a dead-end for concerning myself with revisions.
Worried about water loss and pouring the right amount? Brew too much, thus displacing air in the kettle and preserving thermal insulation. Pour into a twenty ounce container. The end.