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HOW HOT IS YOUR SHOT?
We at Synesso are oen asked "How can I tell if my machine is at the right temperature?" The answer is
more complex than you might think. Several important concepts factor into both the temperature you read
on your machine and the set point you should choose.
The rst major factor in temperature is the machine itself. Many people hold the belief that PID control au-
tomacally equates to accurate temperature at the puck. In pracce, what you get with PID control is a ma-
chine capable of being much more precise than one without such. Accuracy is dened as coming as close as
possible to a known standard. In this case, the temperature you might read from a calibrated external ther-
mometer. Precision is dened as coming as close as possible to a paern. In this case, a stable and repeata-
ble temperature.
Why should we care more about precision than accuracy? The short answer is that there are temperature
probes inside the machine, but not inside your puck. As water is dispensed, it loses heat energy to parts of
the machine, the screen, the screw, the puck itself, even the portalter and basket. We have designed our
tanks and temperature probes to provide the best thermal informaon available to the PID controller, but
aer the water leaves the tank, the water is prey much on its own. The only way to tell how much heat en-
ergy has been lost to the system is to measure the temperature of the water when it is actually inside the
puck. Here at the Synesso factory, we use a specially modied portalter, a ny bead probe, and a trusted
brand of meter to measure that in-puck temperature. Since our machines are designed to be very precise,
we can then adjust the displayed temperature to reect what you will actually receive on your puck. We re-
fer to this adjustment between tank temperature and puck temperature an Oset. Osets translate our pre-
cision to accuracy. Imprecise machines will not be able to sele on an oset as each shot will provide a
dierent puck temperature. Imprecision makes accuracy impossible.
The exact procedure Synesso uses to determine the oset is as follows:
Using a boomless portalter, dose 16-18 grams of coee into our 14 gram basket with a thermal probe
inserted 1/8th of an inch from the surface and in the middle of the puck. Pack and tamp the grounds in
the basket as usual. The thermal probe is then wired to a FLUKE thermometer to measure the actual tem-
perature of the water owing through the puck while pouring a 2 ounce, 25 second shot. Temperatures
measured for the rst and last 5 seconds of the shot are discarded. The remaining 15 seconds are aver-
aged together. This process is repeated a minimum of 3 mes per brew group in order to get the most ac-
curate reading.
Some of our customers have purchased or recreated measurement tools similar to ours. There are also es-
presso machine calibraon tools on the market. The key to using any of these is to develop a simple, con-
sistent procedure which allows you to repeat the tesng at any me, at any locaon, eliminang all varia-
bles except temperature, which you then measure. Keep in mind that dierent procedures will produce
dierent temperature test results, likely resulng in dierent osets than Synesso originally programmed
into your machine. This is not an error. As long as your procedure produces consistent, high precision re-
sults, it is a valid procedure. Keep in mind that procedures that are closer to the act of actually extracng
espresso will result in more accurate osets.
Remember, thermal accuracy is obtained through high precision and careful oset calibraon.
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