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No More Guesswork! Naked Truth of E61 Temperature Revealed
By Dave Stephens
'Help! My espresso tastes bitter/sour!' If I had a dollar for every time that appeared on an Internet forum, I would have a commercial espresso machine. There are numerous articles available on the Internet that discuss the importance of thermal stability. To achieve repeatable results, you must operate within the same temperature range and the initial extraction temperature should be within a degree. Without a reliable method of measuring that temperature it is just guesswork and sometimes bitter, other times sour shots of espresso.
For those of you that own an espresso machine with a heat exchanger, the key is the cooling flush (The best article I have come across on the subject is How I Stopped Worrying and Learned to Love HXs). If you are like me, you have searched the Internet, read every article about cooling flush timing, and intently stared at every graph you could find. Having assimilated all of this knowledge, you're surging with confidence that you can pull the elusive 'God Shot'. You power up your machine and let it heat. In anticipation, you stand there staring at it while pondering all of the knowledge you have gained. You think to yourself, 'I know my brew water needs to be between 195 and 205 degrees Fahrenheit', and then it hits you...
How the heck do I take its temperature?!?
The answer to that question is now at hand, at least for those of you that own an E61 group espresso machine. On the front of the group head is a single Allen screw. That screw plugs a hole that was drilled into the group to create the water channel that your brew water flows through. You can add an inexpensive thermometer through that screw and accurately measure your brew water temperature.
The process is not too difficult, but it does require the use of some power tools. For those of you with some moderate mechanical ability, this will be a relatively easy project. The best part is that it is cheap. The entire cost of goods (provided you already have the tools) is under $30 when using a digital thermometer.
You will need the following items...
- 1. Probe thermometer or thermocouple
2. Rotary tool (Dremel) with a cutoff wheel
3. Hex head stainless steel bolt
4. Drill bits and drill press
5. High temperature torch and brazing rod
6. Soldering pen and solder
7. Heat shrink tubing
9. Thermal grease.
Begin by removing the Allen screw from you brew group. Simply unscrew it with the appropriate sized Allen wrench. Next go to the hardware store and get a hex head bolt about twice the length of the original. Note that the bolt will be in direct contact with water, so be sure to get a stainless steel bolt. You could use aluminum or brass in a pinch (I find these harder to braze and although the soft metal is easier to drill, it also deforms more easily, especially under the heat of a torch; if possible stick with stainless steel), but do not use zinc-coated steel. The zinc bolts will rust! My Isomac uses an A6 size metric bolt but your machine may be different. Take the original with you to confirm the new bolt is the correct size.
While at the store, you may want to pick up a couple extra cutoff wheels, they have a tendency to break at the worst time. You can get the thermal grease at almost any electronic/computer store. I picked my tube up at Radio Shack. If you ask for thermal grease and get a blank stare, try asking for heat sync grease.
Nurse, scalpel please...
Clamp your probe thermometer down to your work surface. I used a piece of two by six and a rubber-padded clamp.
Using the cutoff wheel on your rotary tool, gently cut a grove down the probe housing. This takes a bit of finesse, if you dwell in one spot too long the cutting wheel will heat the probe and burn the wires and sensor inside. Grind one spot for only one or two seconds working your way down the length of the probe. You do not need to cut completely through, just enough to form a crack. Remember to leave two inches at the bottom of the probe uncut. This will become the insert for the bolt and where you reassemble and attach the thermometer display.
Now loosen your clamp and rotate the probe 180 degrees. Clamp it back down and repeat the process. Make two additional cuts, one at both end of the probe housing to bisect the previous cuts. Then gently pry the two halves apart using a small screwdriver or similar tool. Don't be surprised if you have to lightly grind one or two spots so the parts can separate.
Now that it is open, you can see the lead wires that run to the thermal sensor at the end of the probe. Be very careful, the sensor is very small and very fragile; if you tug too hard on those wires, you can separate them from the sensor.
Now remove the probe display from the lead wires and the display base from the probe. I simply cut the base in half using the rotary tool and snipped the probe wires with a pair of small wire cutters. Gently remove the sensor and lead wires from the housing and set everything to the side.
Now you can cut the end of the probe housing off. Do not cut it too short, remember this has to go through the bolt and the display has to be glued back onto it during the final assembly.
Time to drill...
You will need to drill a hole the same diameter as the probe through the center of your bolt. You want a tight fit. Remember this is going back into the brew path where it will be subjected to 9 bar pressure (about 130 PSI).
Center punch the bolt, mount it in a vice on your drill press and drill a hole the entire length of the bolt.
Test fit the probe in the bolt. You need the end of the probe to protrude about 1/8 to 1/4 inch beyond the end of the bolt. If the bolt is too long, cut it down with your rotary tool and cutoff wheel or grind it down with a bench grinder. If you have to shorten the bolt, try screwing it into your machine to make sure you did not damage the threads. You may have to run a die over the end of the bolt to re-cut the first thread.
Fire and molten metal, sounds like fun...
Now we need to braze the probe body into the bolt. Using your torch, heat the hex head end of the bolt and apply your brazing material to seal any gaps. My braze is not the best looking but I am not a professional welder. An acetylene torch is ideal for this. You could also take the bolt and probe housing to a welding shop and have them braze it together for you.
Glue the base of the probe display back onto the shaft and let it dry.
Trim the lead wires for the thermal sensor if needed. Once you have cut the leads to the appropriate length, slide the heat shrink tubing down the leads. Solder the probe display back on. Slide your shrink tube over the solder joint and heat it to shrink.
Apply some thermal grease to the thermal sensor and gently insert it down to the bottom of the probe tube. Snap the display back together and test it to make sure everything works correctly.
Apply a liberal amount of Teflon tape to the bolt and screw it back into the machine. Once you try to screw it back into your espresso machine you will understand why I recommended a hex head bolt. You can use an open-end wrench to screw it back into the group head opening.
Power on your espresso machine and run a water flush through it. Take a portafilter and a blank basket (back flush basket) and lock it onto you machine. Hit your brew lever and let the brew group pressurize; check for leaks. I would recommend pressure testing your new creation prior to the boiler hitting full temp. Getting sprayed by a stream of 80 degree water is much less damaging than a shot of water from a 250 degree boiler. Be careful.
Leak test at LOW temp.
Life! Give my creation LIFE!
Go ahead and let your machine warm up and start your espresso routine.
Temperature at the start of the shot
Temperature at the end of the shot
Want to see it in action? Watch the video. Now you will never have to guess about what your brew temperature is. You are one step closer to consistency and that elusive 'God Shot'.