FRCN Espresso "HOW TO" Pages
by Randy Glass - Copyright 2003 - All rights reserved
E-mail me at firstname.lastname@example.org
Testing Espresso Brewing Temperature
As has been discussed and tested by so many folks, brewing temperature is critical when searching for consistently high-quality espresso. Many have stated that they can taste the difference in a two degree shift in brewing temperature. This leads us into two areas of concern. The first, how to control the brew temperature. Temp surfing, time surfing, the addition of a PID, and adjusting the pressurestat are all ways to deal with that, with varying degrees of success. The second is how to check the brew temperature to see what effect the control has.
Temperature sensors mounted to the boiler are fine, but it's the water hitting the coffee where temperature is critical. A good method for measuring the temp of the brewing water is to have a small-mass, temperature probe mounted right under the showerscreen and hooked to a fast-responding digital read out. Not everyone wants to go to those lengths. There is an easier way to check the brew temp, and while not being very accurate, it can be a starting point is seeking a temperature control point.
Measuring the temperature of a small volume of hot water can be difficult. Water loses heat energy rapidly, and the closer to the boiling point the faster the energy is lost. You can see this easily. Take some boiling water and pour it into a coffee sup with a stick thermometer sitting in the cup. Watch as the temp rises, then rapidly decreases. Being that we are concerned with measuring just two ounces of water (with a correspondingly greater surface-area-to-volume ratio) and you can see how difficult it can be to achieve accuracy. Still, this method can get you into the neighborhood if not to the specific address. It's greatest value is to see if the machine's thermostat is working properly, but it can still be an indicator to show that you are in the brewing ballpark.
Here is what you need:
1) Get a styrofoam coffee cup as is used at fast food places (foam take-away cup). The heavy duty ones used for ice cream and such are good. They last a lot longer.
2) Cut it down until it fits snugly up around the brew-head in the area that the PF fits. The cup I got fits nicely around the outside of the shower screen area. You may have to cut it down about 1/4" (6mm) at a time once you get close to the correct size. The shorter the cup when done, the better. It puts the probe closer to the brewhead and has less volume of air in which the water can lose heat energy.
3) Poke a small hole near the top of the cup but below the brewhead for a vent to release trapped air during the test.
4) Measure out 2 oz. (59ml) of water and pour it into the cut-down cup. Mark the level of water on the side of the cup.
5) Boil some water and "calibrate" the thermometer. Some of them can be adjusted, but just getting an idea of the approximate reading for boiling water will verify the readings you are about to take. Remember that there are a lot of variables that can cause "boiling" to not always be 212F (100c). Do not put the thermometer into an operating microwave.
6) Near the bottom of the cup, about 1/4" or so (6mm) from the bottom, carefully push the stick thermometer into the cup. Push it through one side and then just barely into the far side so that it is held in place. You want it fairly low in the cup so that it is fully submerged in the water during the test.
To use this device, get your espresso machine up to operating temperature as you normally would with the portafilter in place. About one minute before you are ready to test, pour some hot water into the cup/thermometer assembly to preheat it.
Immediately after it is firmly in place, pull two ounces of water using the pre-calibrated mark on the cup, all the while watching the thermometer's reading. It will rise quickly, reach a high point, and then start to drop. Record the highest temperature indicated. You may wish to repeat the test a few times, emptying the cup between tests.
A high temperature of about 195-200F (91-93c) is a good indication that the machine is working properly. Over 205F (96c) probably means it is too hot and under 185F (85c) probably means it is too cold. As with the calibration test, things like water quality, thermometer accuracy, thermometer mass, ambient air temperature, altitude, and more can affect the readings.