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Vibiemme Vibiemme Double Domobar version 3 Manual

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Preinfusion
If you have chosen to plumb your machine to an external water source you have already read that the DD’s
plumbing is pressurized all the time.
*1
Lifting the brew lever at any time, even if the DD is disconnected from
the power source, will allow a steady, low-pressure water flow out of the brewhead. This can be used to great
advantage when making espresso.
For the DD to make espresso, water is forced through the coffee at approximately 130 PSI (around 9
BAR). The rotary pump is capable of delivering that in a very short time once the pump’s motor has been acti-
vated. Because of this quick ramping-up of pressure, it limits the amount of time that the coffee has to absorb
water and expand in preparation for delivering the espresso into the cup. An improvement in the espresso can
be had by beginning the extraction in a slower, gentler way called preinfusion.
Just as the name infers, to preinfuse is to infuse some water into the coffee before actually beginning the
full force of the extraction process. The benefit is that you get a more even, fuller extraction. The “pre-soaked”
coffee also gets a chance to “pre-expand” which limits the chance of water finding an easy path through the
coffee, thus limiting channeling.
How To Preinfuse
1 Prepare to extract espresso just as you always have; grind, dose, tamp, lock the portafilter into the group,
and place a cup under the spouts.
2 Lift the lever to around halfway. When you reach that half-way point you will feel an increase in the resis-
tance to the movement of the lever. A slight amount further is where preinfusion will begin. To verify that
you are a the correct position, watch the brew pressure gauge (the one
on the right), and you will see the water pressure drop slightly when you
have moved the lever the correct distance.
You have opened the brew valve inside the group that allowed water in
the thermosyphon tubes to enter the portafilter (see Chapter 3 for details).
The pressure in the plumbed line is now pushing water into the boiler and
then into the portafilter at low pressure. The coffee is getting wet.
If you move the lever too far the pump may start. No need to panic
about that, but it is best to just lift the lever all the way and allow the
extraction to complete. Once the pump starts, lowering the lever has the
potential to fracture the compacted coffee and ruin the extraction.
3 After starting the preinfusion, count about three seconds, then lift the
brew lever all the way to begin the extraction of espresso. You will notice
that the espresso begins to drip out in a much shorter time than if you had
just lifted the lever fully with no preinfusion.
How long should you preinfuse? There is no rule, as it is simply a
matter of taste. It can be as little as two or three seconds. Some coffees benefit from longer times. You can even
hold the lever in the preinfuse position until the first drops of espresso begin to dribble out of the portafilter
spouts. As with all things espresso we recommend that you experiment. Use three seconds for a week, then
try five seconds the next week and see if you can tell the difference. Or try two seconds. The rule for what you
should do is: do what makes the best tasting espresso for you.
*1 The preinfusion process described above is effective only with a plumbed machine. A DD supplied by
the internal reservoir will supply infusion at the beginning of the extraction process through the design of the
E-61 group as explained in Chapter 3, but this will not be quite as effective as described here, nor does it offer
the duration or control available in a plumbed machine.
… 53 …


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