temperature control and taste
Coffee should never be made at the temperature of boiling water (212) – it is best at lower temperatures. This turns out to be a very important variable in making coffee. If espresso is brewed at too high a temperature it turns out to be bitter. If it is brewed at too low a temperature it turns out to be sour. There is no perfect temperature, but a general range is from 195 up through 205. The best temperature will be based on the beans and the roast an also personal preference.
A word of caution is that temperature control became very trendy and people started to overemphasize it at the exclusion of other variables which were equally important.
I love to fix the other variables and pull shots of a given coffee at a few different temperatures in a row to compare the impact on taste. The goal is then that when you taste a shot you can instantly recognize if the shot was pulled at too high or low a temperature based on your personal taste. This is not a trivial skill though.
One problem is that overextraction can cause bitterness, but it this can be a result of the wrong temperature or the wrong grind, or the wrong dose, so if something is wrong how do you know which one you are tasting? Experience and practice is the only answer I know of.
Now some machines allow control over temperature and some do not. On heat exchangers and levers an approximate control is built into the way you pull the shot, but control down to .1 degrees is unlikely. On single boiler and double boiler machines that control can be added by use of a “PID.” One problem is that the PID usually measures the temperature at the boiler, which is not the temperature at the top of the coffee, and the temperature at the top of the coffee is different from the temperature at the bottom of the puck of coffee, so such precise control is often as much an illusion as a reality. People usually use an offset assuming the temperature at the coffee is roughly a certain number of degrees lower than the boiler, but the key word there is roughly because ambient conditions do change the temperature differential by well over a degree.
On the bright side I don’t know of a single study that shows that people can taste a .1 degree difference in coffee (many people claim they can, and perhaps they can, but you would need a double blind tasting to prove it). It is not hard to taste a 5 degree swing. Somewhere in between is the control you need and for my taste you can achieve that with a heat exchanger (or PID’d machine, of course). It is harder to do on a lever, but possible.
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