Operation Manual

46
Cooling Flush
One of the benefits of the Vibiemme Double Domobar is the thermosyphon built into the E-61 brewgroup.
As you read in Chapter 3, convection recirculates hot water from the brew boiler through the E-61 brewgroup
and back into the boiler which helps create thermal stability throughout the entire brewing path. With the PID
control of the dedicated brewing boiler, the boiler and the group are held at a controlled temperature, ready to
brew when you are. Temperature control and stability goes a long way to helping you get consistent results,
and few machines in any price range can match the DD when it comes to brew temperature control and con-
sistent performance.
You may have read that with some other espresso machines which have a thermosyphon system and E-61
group that a cooling flush is necessary. It is the same with the DD. But since the DD’s dedicated brew boiler
does not have a heat exchanger and it does not have to hold steam, the amount of time (and thus, water) needed
when performing a cooling flush is minimized. Usually just two to four seconds of cooling-flush time will be
sufficient.
The reason to flush the brewhead and heat exchanger is that the water in the brewing path can slightly
overheat. If the water in the boiler was exactly at brewing temperature, by the time it got to the coffee it would
be too cold. To compensate for that the brew boiler is held about nineteen degrees hotter than the desired
brew temperature (this is the temperature offfset discussed in Chapter 12). When the machine sits idling, that
“extra” heat energy can be transferred into the upper thermosyphon tube and then into the E-61 group. Ad-
ditionally, after extended periods of idling, a small amount of steam can build up in the water from dissolved
air in the water that is released. If that overheated water or steam was used to brew coffee you might get an
over-extracted, harsh tasting espresso. The cooling flush eliminates that over-heated water and assures that the
brew path is closer the correct temperature.
A cooling flush couldn’t be much easier: Remove the portafilter and lift the brew lever as if you are mak-
ing an espresso. That’s it - just lift the brew lever and count about three or four seconds as the hot water pours
from the group into the drip tray, then fully lower the lever. Done. Now just grind, dose, tamp, lock in, and
make espresso!
You will find that regardless as to how long the machine has been on, whether thirty minutes or three
hours, about the same cooling flush duration is quite effective. This is due to the advanced design of the brew
boiler and PID system. As you become more accustomed to how your DD operates, and how small changes
affect the taste of the espresso, you can tailor the cooling-flush time to match your tastes. You may find that
after the machine sits idling for more than an hour or two that a slightly longer flush is more effective.
If the machine is in current use, such as when making consecutive extractions, you only need to perform
the cooling flush before the first extraction. After that, the design of the machine will maintain the proper tem-
perature. The cooling flush only needs to be performed when the machine has been sitting, unused and idling
(on) for longer than about twenty or thirty minutes.