Well, we’ve finally got to the bottom of why a very limited number of users (3) reported that their LONDINIUM I had poor thermal stability
It is annoying that it has taken so long to get to the bottom of the matter, and the cause is frustratingly simple, as i suspected it might be
The culprit is long pre-infusion times
Use the LONDINIUM I in the manner that the Italians have done for decades and the LONDINIUM I exhibits phenomenally thermal stability; a pre-infusion time of 3 seconds is the answer
A pre-infusion time of 3 seconds also improves the clarity of the shot. Long pre-infusion times mean you are effectively brewing the coffee during the extended pre-infusion period then applying the espresso process to the shot after that, which compromises the clarity and definition of the shot
If the nay-sayers want something to cling to we’re happy for you to accuse the LONDINIUM I of lacking the flexibility of a pump machine. This is precisely why so many owners love their LONDINIUM I – the absence of a confusing array of parameters to manage. Our customers are busy people who don’t want to play baristas or lab technicians – they want a simple, high quality espresso machine that with a few basic guidelines they can consistently obtain exceptional espresso from. LONDINIUM I delivers this
So, by way of example, the LONDINIUM I is not the machine for you if you want to run 22g doses. It can be done, but its definitely a manoeuvre for the experienced user. A 22g dose is also a bit mad for the shot weight that the fixed volume that a lever espresso machine delivers; you are looking for a brew weight of about 25g, certainly less than 30g. If you just want ‘more’ espresso then the way to go is get yourself an extra portafilter then as soon as you lock the first shot into the group & release the lever you prep your second portafilter. Load the second portafilter after the first shot completes and you will have 2 shots in very quick succession to combine together for a longer shot
The hundreds of hours we spent testing and deploying non return valves, its all completely unnecessary. We have investigated the performance of the seals we use, we have experimented with numerous lubricants on the bore, and none of them yielded a solution
With or without a non return valve a long pre-infusion will compromise the thermal stability of the group
This is not the result of a design deficiency in the LONDINIUM I; all lever groups with a thermosiphon perform in this manner. A heat exchanger with a much greater volume, as found on the LONDINIUM II, means the thermosiphon is more powerful and can restore the group to its optimal temperature more quickly, but a long pre-infusion will still cause the group to cool. Its unsurprising as the group has effectively been disconnected from the heat source the moment the piston is raised
When the piston is raised the thermosiphon is interrupted and immediately the temperature differential between the supply and return thermosiphon pipes diminishes. You use a thermosiphon to avoid the thermal escalation that occurs in a dipper (lever mounted directly on boiler with a brass flange) lever group when consecutive shots are pulled. The additional energy that is introduced to the group from the volume of water in the shot is offset by the interruption of the thermosiphon whilst the piston is raised
However, if the piston is raised for too long the group starts to cool. The longer the thermosiphon is interrupted for the longer it takes to re-establish itself, all the while the group is radiating more heat than is being supplied to it by the thermosiphon, and so the group cools
A pre-infusion time of 3 seconds and your LONDINIUM I will have phenomenal thermal stability and your shots will have exceptional clarity
If you have a LONDINIUM I i look forward to hearing from you after you have reduced your pre-infusion time to 3 seconds. A 14-18g dose, 3 seconds pre-infusion, coffee should flow within about 3 seconds of releasing the lever if it is to extract correctly, then 27 seconds from the shot flowing until the shot blonds, with a resultant brew weight of around 25g
Sorted.