Londinium is a brand of coffee machine that hail from the UK.
These machines have become famous for their unique style of shots
to the point that many baristas have tried to emulate the
"Londinium shot" on other machines.
My moddified Gaggia Classic (Gagguino) and Rancilio Silvia (Gaggimate) have "Londinium Profiles".
The Decent also has something similar.
So what is it?
It's a spring lever machine that uses pressurised pre-infusion at the beginning..
The technique it uses is something like a GS3 puck slam.
It really slams the puck with something like 25mls of water.
This very fast and early saturation of the puck compresses it much faster than is usual leading to a denser & thicker starting pour.
It's sometimes called a "water hammer".
The adapted "Londinium profile" for a standard lever machine involves
quickly hitting the puck with pressure (called the puck slam .. it's about 3-4 bar)
holding it there.
Notice the initial flow rate is about 9ml/s then drops to 0.3ml/s.
The "standard Spring lever profile" has a much lower pre-infusion pressure. (About 1bar)
(3 Bar is also common in "Blooming profiles").
This gets the water through the puck evenly & quickly & hopefully this will result in minimal channeling.
The initial flow rate needs to be really low ... about 8ml/s (0.3 to 0.5g/s) range.
This will give you a beautiful thick top to your espresso.
After this, ramp up to 9 bar, then gradually drop back to zero
as the puck degrades.
Try to keep the flow rate constant during this second stage.
This second stage has much less body.
Sometimes, after the shot reaches 9 bar, the pressure declines more slowly (than in the above Gagguino example) ... or sometimes it even hangs around the 9-8 bar range.
It all depends on the flow rate.... the important idea is to keep the flow rate constant.
When you drink a shot like this it feels super creamy due to the thick top of the preinfusion.
This pic is the graph from my Rancilio Silvia (Gaggimate mod).
I used a DF64v grinder at setting 12. (1000 rpm).
Temp 93c
Pre-infusion 3 bar (14 sec)
Ramp up to 9 bar (1 sec)
then drop to 8bar, 7bar, 6bar, 5bar.
Hold at 5 bar for the rest of the shot until you reach your desired final weight.
I think my grind size was a little to fine ...as it took 43sec to get 36g out.
I'll dial the DF64 to setting 10 next time.
So for this Gaggimate - Londinium profile I decided to maintain the final pressure at 5bar but this could be lower ... maybe 4 or 3 bar ??
Some profiles use higher pressures.
I think it all depends on keeping a steady final flow rate and thus maintaining puck integrity.
In summary:
1. Pre-infuse: 8 ml/s, low pressure & hold at 3 bar.
(About 13 secs). At this point, the puck is held in a compressed state.
2. Post infusion: raise pressure and hold at 9 bar.
3. Final stage: decline to 5-3 bar (and hold at this pressure)
You need to monitor the flow in these last stages.
Your aim is to keep the flow at about 2g/sec (2ml/sec).
This profile works really well on dark to medium roasts.
Usually, I aim for a 1:2 ratio
One important think to note is that although I use the measurement of pressure a lot, what is also important is flow.
Pressure = flow x resistance
This type of shot is really tasty with milk based coffee like Latte
Below is a graph from Decent.
Temp is around 89C
The flow changes quite a bit.
... up to 8ml/sec (puck slam) then back to 2ml/s
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