How to (re-)calibrate an espresso machine and grinder setup? When you're starting your shift at your coffee shop and take over the bar from another barista, the machine and grinder can be in varying states of cleanliness and calibration. How do you quickly and correctly get back to pulling good shots from clean equipment?
This answer addresses a &quot;standard&quot; semi-automatic espresso machine with a separate grinder. Specifically the LaMarzocco and Astoria grinder, but the ideas should generalize to other machines of the same class.
Cleaning
Of course, wipe down everything and get all pitchers and spoons clean. Blast out all the milk and &quot;wetness&quot; from the steam wands. Inspect and clean all portafilters* (get one clean, and then use it while you clean the others), and if necessary backflush the groups with water (with &quot;bumping&quot; so you blast water around the seals to get any buildup there clean).
*especially under the basket.
Calibrating
The abstract procedure here is described using the Hackers' terms Frob, Twiddle, and Tweak.

http://catb.org/esr/jargon/html/F/frob.html
To fully calibrate the setup, we'll need to make three passes over all the controls.

Frob. In the frob pass, we make just &quot;coarse&quot; adjustments to get everything roughly correct. (reinterpreting the hacker usage. This isn't aimless.)
Twiddle. In the twiddle pass, we adjust each parameter up and down a little, in a more &quot;scientific&quot; manner: while adjusting any one parameter, the rest are left alone so they behave as &quot;controls&quot; for the quick little &quot;experiments&quot; to check each change.
Tweak. In the tweak pass, everything should be mostly correct by now. Just apply any finishing touches.

The controls we have available are the grind, dose, and water quantity. Following the David Schomer method, I strongly advise that the tamping pressure should be constant. Always tamp the same way: from the elbow, so you don't stress your wrists.
In the David Schomer method, the dose is controlled by counting &quot;clicks&quot; of the doser. You keep the doser compartment as empty as possible, grinding only what you need so everything stays fresh, locked in the bean). Count how many clicks gets you to &quot;full&quot;, maybe a little heaping. This number is your base dose. Keep it constant for now. And this constitutes the &quot;frob&quot; of the dose.
Set the group in programming mode and Pull a shot, setting the water level to yield 2 oz. This is the &quot;frob&quot; of the water quantity.
If the extraction time was off, adjust the grind. This the &quot;frob&quot; of the grind, so you can make bigger movements if you need to (exercise your judgement), but remember only adjust finer while grinding, so you don't lock the burrs on a tough bean. Pull a few shots until the time is (roughly) correct.
So, we've done our &quot;frob&quot; pass. Now &quot;twiddle.&quot; Adjusting the grind to control the extraction time probably threw off the water quantity a little bit. So do a &quot;twiddle&quot; of the water quantity by entering programming mode and pulling a shot. Actually, you shouldn't need to &quot;twiddle&quot; per se: there's no *up and down&quot; here, but I think the terms still represent a useful mnemonic for the general procedure.
Then do a &quot;twiddle&quot; of the grind. You want the grind to be as coarse as possible within its &quot;range&quot;, if you know what I mean. All the grounds in the doser are quickly going stale. A coarser grind yields little pieces of coffee bean that are slightly larger, with a lower surface/volume ratio. Lower surface area means less interaction with the air, and the grounds resist going stale a little better.
There should be no need to &quot;twiddle&quot; the dose at this point. We're adjusting the other controls so the dose remains at comfortable spot.
Now, one final pass to &quot;tweak&quot;. Pull a shot, and examine its quality. Particularly look for the tell-tale white &quot;overextraction stain&quot; where the last drips struck the crema. You want to tweak the water quantity to stop just before the color changes. This tweak gives you &quot;ristretto-quality&quot; shots.
Adjusting on-the-fly
Remember that we did not mess with the dose much in the above steps. But the other parameters were setup so the dose is &quot;comfortable&quot;. This lets us make small adjustments to the dose in order to &quot;ride the wave&quot; of the machine and keep all the shots in the time range. Remember not to brew shots while the boiler is cycling.
The same three adjustments, frob, twiddle, and tweak, apply also to dynamic adjustments. Frob, the coarsest control is the water quantity, which should no longer need adjusting at this point. Twiddle, the medium-grain control is the grind setting. Unless a freak thundershower rolls-in and totally changes the pressure and humidity of the atmosphere, you should only need to make small adjustments and only to recalibrate the dose to a comfortable level. Tweak, the finest control is the dose.
If a shot pulls 1-second too long, tweak your dose ever-so-slightly shorter. Either count 1-fewer click, or count your clicks just a hair faster.
If a shot pulls 1-second too short, tweak your dose ever-so-slightly longer. Either count 1 more click, or count your clicks just a hair slower.
If the dose gets too low (by visual inspection: exercise your judgement), twiddle the grind a little coarser so you can achieve the same density with more mass.
If the dose gets too high (exercise judgement), twiddle the grind a little finer so you can achieve the density with less mass. (Volume is constant.)
 
I actually haven't worked on this machine in almost 10 years. So this is all based on my memory of that one amazing day when I pulled 20sec (+/-1) shots for eight solid hours.
On a different day, I recalibrated after a thunderstorm started by pulling the grinder 8 clicks (!) coarser. And got it back to 20sec after 2 or 3 pairs.
That's how I know. But I learned this all from David Schomer's book.
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Appendix: The &quot;David Schomer&quot; method or &quot;ritual&quot;
This is what I remember from the amazing book, Espresso Coffee: Professional techniques by David Schomer. And hey Matt, I want my copy back!
A. Preheat and Clean.

Pull an ounce or so of water through the old spent puck to heat the group.

Yank the portafilter and knock the old puck into the compost bin.

Wipe the basket and run a splash of water through the group without the portafilter to rinse the upper screen. (You can catch this water with the portafilter before wiping to rinse more of the grounds so your clean towel stays clean longer.)


B. Grind and Dose.

Turn on grinder to start to fill the doser (which should be as empty as practical).

Immediately start pulling clicks of the doser until the basket is full, or a little heaping.

Turn off grinder.


C. Distribute and Tamp.

With clean hands, distribute the grounds evenly with a finger (I use my ring finger, but whatever works).

Tamp lightly to shape the puck.

Tap the edge with the handle end of your nice aluminum tamper that you bought yourself and brought to work to help. This gets the little bit of coffee around the edge that the tamper missed.

Tamp firmly, from the elbow. About 30 pounds of pressure.

Reinsert the portafiler.


D. Brew.

Click the button to start brewing.

Immediately discard the hot water from the shot glasses which is still there from step A.1.

Watch the pour and stop it early if you need to, to catch the sweet spot.


And finally, I apologize for my excessive use of emphatic &quot;quotation marks&quot;.