THE PRACTICAL GUIDE TO STRADA EP HUSBANDRY
The Practical Guide to Strada EP Husbandry - or how I learned to stop worrying and love the paddle.
I've just taken delivery of a new La Marzocco Strada EP, one of the new generation of machines designed to deliver the best espresso possible.
This is a machine I have lots of experience of as an engineer, but until now limited practical experience of use in a cafe environment.
For those of you who aren't aware, it has features found on similar level machines such as individual brew head tanks, PID control with the added ability to control the pump pressure individually for each group.
This is all well and good but as I have mentioned before, pressure profiling is just another tool we can use to effect the extraction of our espresso and not some mythical process by which perfection can be attained. More often than not it opens more doors than it closes.
Lets break down the Pros and Con's before we go any further:
Pros
Individual Group head tanks with PID control for temperature stability.
Separate steam tank for long lasting steam
Individual Group head pumps with variable electronic control for pressure profiling
on-board CPU for pressure profile playback
Solenoid steam valves for minimal heat loss (minimal condensing) and low maintenance
"soft" water delivery via gear pumps and flow restriction.
Cons
Pressure sensing system leads to false feedback to pump control
VST style baskets "too good" emphasise issue with pressure feedback
Lack of support and education on how pressure effects extraction and therefore taste.
Odd design features; water mix jog wheel, steam tube position, steam lever
The Pros all add up to the Strada being capable of producing espresso of exception clarity and complexity, the Cons can make this an arduous and problematic process, lets look at them in further detail.
Odd design features
For a machine at the highest price point a few small details niggle slightly and although they are ultimately issues that don't effect the ability to produce espresso, it would be nice to see some updates to further models.
Cool touch steam wands - seems pretty odd that the Hot water is cool touch and the steam wands aren't no?
The Water mix jog wheel - we hardly use it, but it seems like an after thought with an unsightly notch cut into front panelling - why not make it a nice lever?
The drip tray - doesn't drain effectively, not exactly a hardship but a niggle all the same.
Steam Wand positioning - could do with being a little taller to allow a little more room to the side of the machine and make steaming more comfortable.
The Steam Lever Knob - not very nice.
Pressure Sensing
This is the root of the rest of the issues you have to overcome when using the Strada.
To help understand how the Strada is different, it's useful to read the excellent post on this subject by Nick Cho of Wrecking Ball in San Francisco Nick Cho Tumblr Post
Done yet?.........
good, lets move on.
In a nutshell, the Strada senses pressure the pressure differential at the face of the coffee puck, it uses this feedback to control the speed of the gear pump and so the pressure of the water flow.
The problems arise if we experience choking or channelling In both cases the machine reacts adversely to the pressure feedback it receives reducing pump speed in the case of choking and vice versa. This effectively amplifies the problems leading to huge problems in maintaining consistent extractions.
Nick outlines a simple mod you can affect to alleviate this problem (although it will invalidate your warranty) and I know from speaking to LM bigwigs that this is a problem they are looking into.
I believe that the problem becomes more apparent when we ask the Strada to hold a particular pressure for a period of time. When doing this the machine is constantly altering the pump speed to maintain the desired water pressure, this in my experience made it more susceptible to the erroneous feedback loops.
The combat this I've recently changed the profile for one that keeps the pressure gradient constantly changing.
Profile 1 - 10 second pre-infusion @ 3 bar, 3 second ramp to 9 bar, hold 9 bar until 27 seconds, 3 second ramp down to 0 bar.
Profile 2 - 15 ramp up from 0-12 bar, 15 ramp down from 12-0 bar
Since switching to this second profile, I've found that the shot weight has been far more consistent (we weigh dose and shot weight for every shot at the shop) resulting in a more consistent quality and fewer wasted shots.
I'd still like to try the Cho mod, but that is for the future.
VST - the basket that dare not speak its name.
Much was made of these baskets, developed by Vince Fedele, on their launch a few years ago and I'm not disputing their quality in any way. Its just that they may be "too good" for use on the Strada as it currently exists.
The even hole size and distribution seems, in my experience, to encourage the flow to accelerate in the second half of the shot.
Now imagine we have a channel in the puck and also imagine that the Strada senses this and increases the pump speed to maintain the pressure at the puck.
What happens is that the accuracy of the hole size and distribution on the VST's provide no resistance to this feedback loop, so the flow increases, pressure drops and the pump speed goes up and so on until the program finishes.
What we see is the precision of the VST basket effecting the feedback loop in a way that a less accurate basket does not.
I've switched the baskets we use to Synesso triple baskets and since doing so have experienced far more consistent extractions/shot weights than with the correct size VST basket.
These ridgeless baskets are still of high quality, but not to the level of precision of the VST's.
Don't misunderstand, we still experience choking and channelling , but they are easily delay with by adjustments to distribution or grind in the normal manner and are more easily diagnosed.
Once the feedback issue has been addressed then I believe that the VST's will become the basket of choice.
Support and Education re: pressure profiling
Imagine your buying a new pressure profiling machine, it arrives and you cant wait to start pulling shots, but what profile do you use? How does pressure affect the extraction?
Give up? google it. No seriously. Before La Marzzoco USA's recent Pressure and Flow series of events, you'd be stuck googling some articles by James Hoffman or Nick Cho, and then trying to apply some of that on the machine yourself.
This is no bad thing, but what if you just need a profile that works? why isn't there a resource for this? Why isn't anyone sharing their profiles?
LM have said that they are looking into a forum for sharing profiles, those that work and those that don't, but it would be of benefit if the machine came with tested and proven profiles already programmed in and ready to go.
The 2 profiles detailed above are the best of the dozens we have tested. They can produce consistent results and take advantage of the Strada's ability to customise your pre-infusion.
All in all, its a wonderful machine, you just need to pay care and attention to your recipes and perhaps try changing your profile and baskets.
I've you've been having similar problems or have different experiences please leave a comment below.
MADE BY