Renés notes from talks with the designers and builders of:
Slayer, Marzocco, Synesso
Different ideas:
Pre-infusion with set pressure- just like the bloom stage of soft brewing, wetting the puck to swell it and fill all the gaps between grind, to ensure full saturation, to allow brewing to start without pressure so no channeling will occur. This also will stop “fine grind” being pushed thru the gaps to the bottom of puck and clogging, with PI they are trapped where they sit as the coffee swells.
Post infusion with set pressure- allows the bar pressure to be reduced at end of the shot- to be able to continue extracting good solubles and flavours out of the coffee without over-extraction with high pressure, just like a lever espresso machine
– direct response in bar pressure, relating to changes on made on paddle, visible on manometer,
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Slayer: Jason Prefontaine
Slayer has a 2 stage brewing potential, pre-set on both stages- ie 3 bar, 9bar
It uses a mechanical brew head (and paddle) to switch between 2 pipes feeding hot water,
Stage 1- is Pre-infusion (using an adjustable tap inside machine) set on eg:3 bar,
Stage 2- to select main brewing pipe, eg:9 bar.
Towards the end of shot you can return paddle to stage 1, but it won’t simply return to 3 bar, can vary greatly in post-infusion stage due to residual pressure remaining in puck. So post-infusion isn’t very reliable/ useful.
Weakness- mechanical brew head requires bi monthly seal changes inside head, requiring full machine shut down.
totally manual means its not possible to perfectly replicate shot profiles in cafe.
Recommends only using one brew head at a time as muli use will reduce overall pressure on each group due to only 1 pump. (same as most machines which don’t have pump per group)
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LM: Scott
La Marzocco Strada (MP) Mechanical paddle and (EP) Electronic paddle
MP- has a variable brew pressure paddle, and manometer dial on top of each group to see pressure changes. But usability is very hard as the amount of room you have to move with paddle from 0 to 9 bar is about 1cm, I couldn’t get any useful pre-infusion from these machines, would always show no pressure on dial or quickly ramp up to 9 bar. Therefore this seems useless to me, and almost everyone I’ve talked to doesn’t use pre-infusion on these machines.
EP- Uses a geared pump to progress “varied pressure brewing” (unique to EP I think) it electronically changes pump speed to deliver diff bar, all water is delivered via one feed.
Uses electronics to program different brew pressures during extraction. You can chose any pressure settings, or run shots manually with paddle. No manometer dials on group heads. This machine is touted as designed for pressure profiling, but would be best used for pre and post infusion.
Weaknesses:
Both Strada’s also have wear issues with the mechanical group head, need seal replacement regularly requiring full machine shut down, and has wear / casting issues. Also paddles don’t like hard use, it misaligns internals making the paddle useless till repair replace internal parts which have bent or broken.
Recommends only using one brew head at a time as multi use will reduce overall pressure on each group due to only 1 pump. (same as most machines)
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Synesso Hydra: Mark Barnett,
Hydra uses the 2 pipe water feed to separate bar pressure.
Stage 1: pre-infusion on inline pressure
Stage 2: even ramp up to 9 bar, taking a few seconds
Stage 3: Extraction at 9 bar
Stage 4 post-infusion on inline pressure
All stages have adjustable taps to change bar pressure.
The Hydra has an electrical switch assembly not mechanical so group head requires no maintenance!
Volumetric is programable to run these pressure settings and stop shot.
Paddle groups can be programed to have first 3 stages programed (you push paddle all the way across) and the ability to start post-infusion when ever you like, by swinging paddle back to stage 1, then off.
Paddles prefer gentle use also, but won’t damage internal parts if heavy handed.
Hydra has a pump per group designed for simultaneous group brewing- no pressure loss.
All these machines have similer modern tech- Saturated group head, PID temp controls, dual boiler etc
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Pressure profiling and pre-infusion has to be replicable every time to get flavour consistency, ie electronically controlled, This eliminates Slayer and MP. The EP has mechanical group which by all accounts needs regular servicing, but has great LM tradition of quality,
By all accounts full pressure profiling opens a can of worms, too many variables during changes of pressure. None the rockstarts of espresso I spoke with at SCAA had anything good to say about Pressure profiling relating to cafe service, but they agreed pre and post infusion has merits if it can be replicated every time.
The Cooling Tray Sessions 
