Variable Pressure Infusion Modification Results: Joint project between Mark Barnett, Synesso, and Herkimer Coffee
Below is a document I am sharing, with permission from Synesso, in very raw format.
I came across this document a while ago in a coffee shop near my office (Valentine Coffee Roasters) which runs with a Synesso Hydra, they were using this document as a guide to tweak their pressure profiles. I took the opportunity to guerilla snap photos of all the pages for future reading and experimentation, hence the fantastic quality of the photos below.
I later got permission from Synesso to share the document in a public space since I felt it would be interesting and possibly of use to home baristas who like to tinker with these sorts of things. This is one of the reference documents I used while playing experimenting with Pressure Profiling Techniques for Spring Levers
. I found it quite nifty that a document initially about their attempt to make a modern pump machine mimic a spring lever taught me how to be more versatile with my spring lever.
I also found the 6 criteria under which they base their shot quality and their description of how each of them affects the outcome of the espresso very interesting in its own right, so even if the pressure profiling aspect of the document isn't of interest to you you may find some interest in how they describe the different espresso shot criteria and how they are affected.
Interspersed with the pages are some of my observations on content within them as well as any notes that I feel may make certain sections easier to understand.
Synesso also offered to send me a better quality version of the document, but they haven't yet; no problem, they are quite busy so I've decided not to nag them about it.
The first thing you will probably notice is that they list all their pressures in the document as psi. I'll convert them to bar for easy reference:Control Phases
Initial (Stage 1) Preinfusion: (45psi) ~3 bar
Secondary (Stage 2) Preinfusion: (90psi) ~6 bar
Full Pressure Infusion: (125psi) ~8.6 bar
Dropback Infusion: (90psi) ~6 bar
To note in the paragraph that starts with "Tiny bit of background info" they state that they focused on mimicking HX levers and ignored dipper levers due to low (~1 bar) initial preinfusion and "inconsistent nature of direct water flow from the boiler"
So essentially they had in mind something like a Brugnetti Aurora rather than my Faema dipper.
I was undeterred, mainly because I don't understand what they meant by "inconsistent nature", and also because I'm less convinced than they are that a 1 bar preinfusion has much of an effect on the coffee unless it's preinfusing for 15 or more seconds.The "Sweet Spot" in bar pressure
Initial Infusion Pressure of 3 bar. Duration of 4 seconds.
Secondary Infusion of Pressure of 6 bar. Duration of 3 seconds.
Full Pressure Infusion of ~8.6 bar. Duration varies from 8 to 11 seconds.
Dropback Infusion Pressure of 6 bar. Duration varies from 3 to 5 seconds.
As preinfusion progresses acidity moves from piquant and nippy to sweet to metallic and acrid
Lower pressures cause this progression to be slower (at the cost of sugar development), higher pressures cause this progression to go faster.Acid
at 45psi (~3bar) preinfusion:
0-2 seconds: nippy or piquant and faint
2-4 seconds: from piquant to sweet
4-6 seconds: from sweet to metallic or acridSugar
An interesting observation with sugar is that the full pressure portion of the shot should be shortened as coffee ages or on more humid days to bring out more sugar.
An interesting piece of info I gleaned from the "Sugar" section is that a declining pressure profile can lend itself to sweeter shots by allowing more time for the sugars to develop while inhibiting phenol development. A 8-9 second full pressure phase is desirable according to the sugar section.
Here it is said that the "drop back" pressure should only last 4 to 5 seconds before the negative effects of phenols kick in. It is important to note that a "drop-back" is only an approximation of what a spring lever does. The spring steadily ramps down the pressure, a "drop back" drops immediately back to whatever pressure the stage 2 preinfusion was set at. Thus, a Synesso doing 9 seconds of full pressure then 4 seconds of drop back is not exactly the same as a lever which really only hits full pressure for a few seconds before starting its decline steadily back down. In my opinion this would cause the desired timeframe for these equivalent stages on the lever to be a bit longer.Spice
(and everything nice)
The spice section talks a fair bit about the "spice" perception being largely affected by burr geometry / size. I imagine that all flavor attributes are affected to some degree by this; I guess they felt the effect was most pronounced with spice perception. Texture
Essentially it was the Texture and Viscosity sections which caused me to experiment with a version of the "2 stage" preinfusion with the lever, looking for a way to increase body with lighter coffees. I've had enough success with it that I still use it semi-frequently with very light coffees, especially the finicky ones.
The following artisanally rendered graphs show the "Quality" scores of each of the depicted attributes as a function of the amount of time the extraction is in that stage. They determined the "sweet spot" listed above basically by finding where all the peaks correlated on each of these graphs.