Anyone who journeys towards the perfect cup of hand-crafted coffee has to find a way to bring water to the perfect temperature. Ideally, we would heat only the perfect amount of water to just below boiling, brew some amazing coffee, and be done. Ah… but life rarely allows for simplicity. The coffee gods like to toy with our technique!
In reality, hand-crafting a brew often leaves us with leftover water in the kettle, be it a little or enough for the next brew. So, should you toss that water out, or should you re-boil? The common wisdom seems to be….
OK, let’s take a brief detour into science. In particular, let’s go back to that dread high school class that many slept through, only to regain interest when Breaking Bad hit the airwaves: Chemistry.
Water is a powerful solvent, and that includes gasses. It may seem counterintuitive, but there are gasses trapped within water, but to varying degrees. Temperature, other solutes (such as salt in the ocean), the mixture of gasses present, and a few other factors influence how much gas is dissolved. If you really want to get specific, point the ol’ Google machine towards “Henry’s Law”, but make sure to brew a fresh cup to keep you focused. The bottom line is that water dissolves gasses, but dissolves less as it gets hotter. For empirical proof, watch a pot on the stove next time you heat some water. Well before you reach a boil, small bubbles will form. Those bubbles are the dissolved gasses coming out of solution, whereas the big bubbles of a boil are water going from liquid to gas.
Ok, are you still with me here? Well, when you heat water, especially if you reach a rolling boil, you expel a lot or most of the dissolved gasses. That leaves the water tasting flat once you let it cool. So, the obvious conclusion is that once you heat up the water, it is doomed and must be tossed. Duh. Obvious.
Well…. I am in the “maybe” camp. In the Phoenix valley, water is scarce, and good tasting water takes work. I don’t toss that out lightly. Water will re-dissolve gasses, and you can help by giving the water a bit of the old “Shaken, not stirred” treatment. The air will slosh around with the water and quickly dissolve as much as the water can hold.
But further than that, once you heat water, you expel a lot of gasses anyhow, so brewing hot coffee, by definition, requires water with little dissolved gas. This stuff is getting crazy!
In reality, there may be a select few mutants among us who can taste the difference between heated and re-heated water for coffee. Those people are sommeliers or professional coffee cuppers, and do not represent 99+% of the human population. I hereby dare you to have a friend:
· heat water
· brew a cup
· add water to the kettle
· re-heat the water
· brew a second cup
· place them side-by-side for you to taste
You will not be able to tell the difference, assuming your friend has consistent technique, and does not wink at one cup to give you a hint. Of course, you could make a lucky guess, so try to do that 5 times in a row. I double dog dare you.
Once you finish the test, let us know in the comments section if you were able to tell the difference. I just failed my own test, and am proud of the result!