Posted Tue Nov 30, 2004, 10:59am Subject: Fine Tuning Brew Temperature on a Heat Exchanger Machine - A Workable Solution
Espresso machines using a Heat Exchanger can produce incredible espresso shots, as we all know. Assuming all conditions are met: Fresh coffee, proper grind and tamp, and brewing Pressure (8.5-9.5 bars), the determining factor will be brew temperature. Brew temperature is the hardest thing to regulate on those machines and coming up with a workable routine that will consistently produce a 202 f brew temperature is a challenge. The solution of course is flushing the H/X of its hot idle water before you pull the shot. The question is how much to flush, and when. It was Dan Kehnís excellent article on the topic that launched me on that quest. click here
Danís method, as good as it is, requires some talent and a keen eye if you want to hit your brew temperature with a precision on 1-2 degrees. It is especially true when dealing with short idle times. The alternative is a flush chart.
So, after long hours with thermometers and thermocouples I came out with the following chart: It can be summed up as a graph where one parameter is the time the machine was on and idle, and the other is the quantity of water that is required to flush it down to 201-202 degrees f. Read the attached document for the details.
MPantani Senior Member Joined: 16 Oct 2004 Posts: 124 Location: Seattle Expertise: I love coffee
Espresso: Isomac Millennium Grinder: Pasquini Moka Drip: Never
Posted Wed Dec 1, 2004, 9:13pm Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
Thanks for the work!
Somewhere I saw an attempt to install a thermocouple in the brew group of an e61. I recall a picture of it being installed where the allen bolt is on the front of the group (where the high-temp warning label is placed in Isomacs).
fateagk Senior Member Joined: 2 Jan 2004 Posts: 102 Location: Tampa, FL Expertise: I love coffee
Espresso: Andreja Premium, Pid'ed... Grinder: Mazzer Mini Roaster: iRoast
Posted Wed Dec 1, 2004, 9:24pm Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
I think you are referring to AndyS's (attempted?) E-61 mod that is on his picture page. I don't know anything about it, but I imagine there is an old thread on AC that these pics belong with. He seems to be quite the Silvia Mod Man!
Posted Thu Dec 2, 2004, 2:52am Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
I did not mention it in my post because I assumed it is well understood, but you must heat your machine for 25 minutes or more before you pull any shots. It is standard procedure with H/X E61 machines.
Posted Thu Dec 2, 2004, 4:23am Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
One last thing: Since you have only 25-30 seconds recovery time, at which time you need to grind,dose and tamp, it could be challenging to do a good job at it. I found that it is much more effective to do the following:
Take the portafilter basket out of the portafilter, and mount the portafilter back into the group head to keep it warm; Wipe dry the portafilter basket using a towel; Grind, dose and tamp directly to the portafilter basket; Flush, start your stop watch; Insert the portafilter basket back to the portafilter, mount it back to the grouphead, wait 25 seconds from the end of flush, and pull the shot.
There is a theoretical problem in that routine: you might say that the portafilter basket temperature is lower than the portafilter's when you pull the shot, and this may affect the shot quality. Though this argument is theoretically sound, in practical matters it does not produce any noticeable difference in the cup. This routine allows for better attention to dosing and tamping and thus reduces the possibility of channeling. It is also much easier to level the tamp when tamping directly into the basket.
Posted Thu Dec 2, 2004, 5:19am Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
This is a real interesting thread, and a great idea!
It seems to me like the HX machines may vary though, due to the design and construction differences in the brew path of various manufacturer. SO - I'm particularly interested in how the results for the Giotto compare to the Tea.
Posted Fri Dec 3, 2004, 1:58pm Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
Thanks for posting this topic. I have an Andreja and would like to find an easily repeatable way to know what the brew temps are like I did on my PID'd Silvia. To that end I was interested in your post because I've heard that the GP is similar to the Andreja and in fact that they share many of the same components. But the amounts of water you are flushing seemed too high to me (maybe there are more differences between the two machines than I thought, particularly the length of the HX) so I made some data-logged measurements of my own and found that my initial reaction that the flush amounts are too high [for my machine] was correct. For example, after sitting idle a period of time longer than "16 & over" a flush of 8 oz. takes the temps from a max of 210 deg F down to 185 deg F. Even if I wait 35 secs, the next pull brings water with a maximum of 192 deg F and not 202 F. I'll bet a flush of 8 oz. will empty the HX and bring in some not-yet-heated-enough water.
I wonder if you have, and would share some of the flush water temps and your pstat setting. That may help me to understand the large difference in our brew temps using this method. And again, thanks for your work and for posting this.
tom_b Senior Member Joined: 19 Aug 2003 Posts: 537 Location: Maui, Hawaii
Espresso: Rancilio Silvia/PID Grinder: Nuova Simonelli MCF Roaster: USPS/Popper
Posted Fri Dec 3, 2004, 2:29pm Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
The method of measuring brew temp will make a big difference. I found that before I got a 36 gauge tc and ran it 'over the lip and under the screw', I didn't get very reliable results, as differences in pressure from using a single basket with a hole poked in it (putting tc up thru spout) made for different results. Even with the under the screw method I get different readings for a 20 second shot than a 30 sec one. The thing I like about the method is that you can make your normal shot and test a 1.5 oz ristretto in 30 secs or what have you. tom:) 'this year's gift for my coffeekook habit - an omega hh501at!!'
Posted Fri Dec 3, 2004, 3:15pm Subject: Re: Fine Tuning Brew Temperature on a Heat Exchanger Machine
I can see three parameters that may produce different results, and as I mentioned in my post, the flush quantities may differ between machines due to those differences. The parameters are:
1) Water temperature in the tank 2) The heat exchanger design. 3) Accuracy of your temperature measurement - how accurate is your thermometer reading?
I used an OMEGA HH506RA with a 24 Gage thermocouple. I snaked it into the portafilter through the bottom of a single spout, and then through a hole I drilled in the portafilter gasket and into a sponge. The exposed end of the thermocouple was slightly above the top of the sponge. The sponge simulates ground coffee. I have found that using a different thermometer, and even a thinner gage thermocouple, gave me less accurate results. Also placing the thermocouple in a different location gave a different reading.
Water Tank Temperature: It ranges from 86 f to 110 f. After the machine was off all night and then on in the morning for 30 minutes, the temperature in the tank will be around 86 degrees. If it is idle for an hour or more thereafter, it may reach 110 degrees. Flush quantities will change slightly if you are refilling the tank with cold water. That is: flush less, about 0.5-1.0 oz less depending on idle time, and add 5 seconds to the recovery time.
If I find the time this weekend, I will run some tests which will include tank water temperature, and update my chart.
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