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Controlling Brew Temperature
If Pulling shots by the Numbers seemed too easy to be
true, that's because I left out one step—brew temperature
management. If you have the Alexia with the PID kit installed, it really
is that simple. The PID affords the user one degree temperature control
precision with absolutely zero fuss. See the section to follow on PID
If you have the Alexia with the stock thermostat, the brew water
temperature will have some natural variation due to the thermostat's
deadband (temperature range between on/off as shown in the graph below).
If you want very consistent results, you need to follow a process
referred to as "temperature surfing".
To be fair, this is an optional step, but if you want to get the
same great tasting coffee every time, or if you want to experiment with
results from different brew temperatures, temperature surfing is how
this is done with the stock thermostat. Alternatively, you could choose
very temperature forgiving espresso blends. Caffe Fresco's Ambrosia
espresso blend is one example of a temperature forgiving blend. Ask your
favorite roaster what they might recommend for a temperature tolerant
Temperature Surfing Explained
When I received the Alexia, I broke out my new "toy", a Scace
thermofilter, and set to work trying to get a feel for the machine's
brew temperature profile. As delivered, I was observing temperature
measurements of 199-201°F at the high side of the boiler's heat
cycle. I used the machine as delivered for the first week with good
results as I finished up some Intelligentsia
Kid O's Organic Espresso blend. Later I
adjusted the thermostat ever so slightly up. At the adjusted thermostat
setting, the highest temperature I registered on the thermofilter was
After a bit of testing with the thermofilter and visual
observation of the temperature measurements, I determined that the
thermosyphon and group needed to be "woken up" from a long idle period.
If you just walk up and pull a shot, the brew temperature will be cool (I saw as low
as 185-186°F via the thermofilter).
By trial and error, I found that I could consistently pull shots at
the high end of the current thermostat setting using the following
- Warm up flush.
In order to wake up the group/thermosyphon, flush about 3-4
ounces, wait, and maybe flush again and wait until the heater cycles on
(Tip: as mentioned previously, use the warming flush water to heat the
The first flush is to warm the group from a long idle. Any
additional flushing is not to heat or cool the group, it is intended to
force a boiler heater cycle so the we can use the thermostats deadband
to "temperature surf" the boiler for different brew temperatures.
Looking at the graph of measured boiler temperature to the right, I
think you'll understand the brew water temperature will be different
depending on where in that cycle the espresso shot is pulled.
- Pay attention to the heating element cycle.
Once the heater light goes off, wait 40 seconds, pull another one
ounce warming flush, and then lock in the portafilter to pull the shot
at/or near the top of the brew water temperature cycle.
The above surfing procedure resulted in fairly consistent
202°F thermofilter brew temperature measurements at the current
thermostat setting, compared to the 10°F swing without temperature
Temperature surfing is a trial and error process. The above steps
should work for other Alexia machines, but the brew thermostat
setting will likely be different. The location of the thermostat's
capillary tube, ambient conditions in your kitchen, etc., may also play
a role in the boiler's heat cycle behavior. You could try following the
above procedure to consistently pull your shot at or near the same spot
in the boiler cycle, and then adjusting the brew thermostat up or down
until you get the desired results. You could also try waiting shorter or
longer periods of time after the heater light goes off (or on) to
achieve the desired brew temperature.
Warning: Geek speak alert! The next sections cover the why
and how of Alexia's optional electronic brew temperature controller
(PID). Engineering types will find it fascinating, others may find it
painfully boring. If you're in the latter group, feel free to skip to
the next page, Steaming
PID Kit Performance
Current brew temperature (left), set value (right)
"OK, so what the heck is a PID controller and what is it
good for anyhow?"
Back in the day, some smart fellas (and current HB members) Greg
Scace and Andy Schecter decided to add a PID (proportional-integral-derivative)
controller and thermocouple to their home espresso machines to replace
the wide deadband (30°F!) and non-adjustable brew thermostat. They
started a craze that has lead to improvements and advancements in both
the home and commercial espresso world with regard to brew temperature
management and control.
By replacing the stock thermostat with a PID
controller, and spending some time properly tuning the controller, brew
temperature set points can be set in 1°F increments, but actual
intrashot brew temperatures control fluctuates based on many
different machine-specific variables (location and precision of the
thermocouple, PID controller, ambient temperature, temperature of the
inlet water, machine hydraulics, etc.). What a PID controller offers to
the typical end-user is repeatability or consistency and adjustabilty.
When you walk up to use the espresso machine, the waiting brew water is
at some steady-state value, X. You shouldn't really care what the value
of X is, you can just be thankful that it is consistently X, and not Y,
or Z. The starting brew temperature of an espresso boiler controlled
by a traditional thermostat could be any
temperature value within the range of the deadband (as great at 30°F
as noted on some machines).
This article does not discuss the installation of the PID kit
because it comes with a 40+ page document covering it in exacting
detail. If you want an idea of what's involved, refer to the The
Bench thread "Buyer's
Guide to the Quick Mill Alexia". Although the documentation is written
clearly and accompanied by a panoply of photos, you should consider
letting the professionals at Chris' Coffee handle it if you are the
least bit hesitant about installing the kit yourself. The fee is a
reasonable $50 to install it before shipment.
For the technically minded, let me share just a few notes on the
kit. It is complete and well thought out. Everything you need to install
the PID temperature controller and insulate the Alexia boiler is
- Pre-configured and calibrated PID controller,
- Custom made thermocouple,
- Wiring harnesses, zip ties, thermal paste, etc.
There are no wires to cut or strip, everything is pre-assembled
for you to simplify installation. As mentioned earlier, the PID kit
installation manual is very thorough and detailed (40+ pages with
pictures). Could you put together a kit yourself? Sure you could,
but it may be 'penny wise and pound foolish'. It would take a
considerable investment in time and resources to source all the items,
implement and test the configuration and have no vendor support in the
With the PID controller kit in the Alexia, both intrashot
(temperature fluctuation within a shot) and intershot (temperature
fluctuation comparing back-to-back shots) performance is excellent. Dan Kehn, who participated in the
evaluation of the Alexia, commented
"These are the best intershot temperature consistency measurements I have ever recorded."
Below are graphs showing intrashot and intershot performance with
the Alexia PID kit (with heater-cutoff relay) installed. This procedure was followed:
- Warmed machine with portafilter and Scace thermofilter
installed for 60 minutes minimum,
- Portafilter removed and pulled a warming flush of ~3 ounces,
- 2 minute recovery and then pulled a "garbage" simulated shot
(data captured this as Shot A)
- Pulled 5 shots with 2 minute recovery between shots, start
dump of thermofilter for each shot (Shots B-F),
The graph below shows six shots (Shots A-F) with two minute
recovery times. The PID SV this go around is 221°F. Shot A, the
"garbage shot" was a bit cooler, but not by much. Here are the maximum
temperatures for shots A-F: 198.3, 198.6, 198.8, 198.5, 198.3, 198.0.