For 15 years I’ve had the same espresso machine. A Nuova Simonelli Mac single group commercial heat-exchange machine that I got of the local eBay and restored to mint condition while I was still in university. It has served me well all this time. It must have produced some 15.000 double shots since I first got it.

A comparable Mac Digit. My mac has a simple on/off switch instead of programmable doses.

To be honest not all of them were good. I quickly found out that my stepped grinder that I was using with my previous Delonghi espresso machine was not up to the task of grinding coffee for espresso, so it had to go. A few grinders later I ended up with a compak K10 WBC, so at least the grinder part is sorted for now.

The Compak K10 WBC 68mm conical burr grinder.

Over the years, like many coffee enthusiasts I’ve found that consistency is key in making a good espresso. So I started paying attention to dosing the coffee, which means weighing your dose. I also started weighing the amount of espresso that comes out to target a specific brew ratio.

A coffee scale. Invaluable to make consistent espresso at home.

I tried to improve my technique as well, but with a limited amount of cups a day I had to resort to technology again, which is why I use a WDT, leveler and a calibrated tamper for my puck prep routine.

Finally I tried to gain insight into the temperature characteristics of my machine by using a fluke multi-meter and K-type temperature probe to measure temperatures during a cooling flush and inside an empty portafilter.

I’ve found a routine that works for me to create great espresso, but it’s a bit messy and it’s so laborious that my wife refuses to learn the routine. I’ll outline it below:

  • Preheat two cups if not already heated with water from the boiler.
  • Clean up any stale coffee in the grinder chute and doser.
  • Grind the coffee for approx five seconds until one of the doser chambers just overflows.
  • Blow any grinds out of the chute as there is approx 1g of retention.
  • Get the scale, place empty portafilter (with dosing ring) on top of it and turn it on. It will set itself to zero with the portafilter on top of it.
  • Dose e.g. 19 grams of coffee.
  • Use WDT to distribute.
  • Use leveler to level the coffee bed.
  • Use tamper to tamp.
  • Remove the dosing ring.
  • Do a cooling flush of the machine, waiting for the hissing of boiled water to stop and subsequently let flow for a second or five.
  • Place portafilter into the espresso machine.
  • Place scale under the machine, place either one or two cups on the scale
  • tare so that it resets to zero.
  • Start scale timer and machine at the same time. (These last 4 steps need to happen quite quickly to avoid the temperature creeping up again).
  • Get around 38 grams of coffee out in roughly 25-30 seconds. Adjust grind or dose a bit to fine tune between shots.
  • Clean up the portafilter and do a quick flush of the group head to clean.
  • Stir and drink espresso.
The routine works and creates great espresso.

So during the lock-down I came up with an idea to improve my espresso machine and grinder. I’m going to convert my Nuova Simonelli Mac into a Nuova Simonelli Mac Tesla with a big tablet bolted onto the front of the machine. To avoid any issues with Elon and with a nod to the original Mac Digit model from NS, I’ll call it the Nuova Simonelli Mac Digital.

Crappy artist impression.

It will be controlled by an Arduino, connected over WiFi to the tablet (or any other mobile device in the house, and even my home automation system). I will add a 230v socket at the back as well, controlled by a Solid State Relay to precisely control the grinder and grind time of a dose. I’ll convert the lower drip tray to a built-in precision scale to weigh ground coffee and extracted coffee. The list of features I could come up with is this:

  • Turn the device on/off with the tablet or remotely (the Arduino is powered all the time).
  • Control and adjust boiler-water temperature (direct) or through pressure (indirect).
  • Control brew temperature through an automated precise cooling flush / boiler temperature adjustment and/or water level in the boiler.
  • Control grind time using a timer with a 10ms resolution.
  • Control ratio / brew weight through a built in scale that will automatically stop flow when desired weight is reached.
  • Log every parameter during the brewing process.
  • Automate group head screen flush after a brew.
  • Automate the cleaning back-flush.
  • Add pre-infusion to the machine by independently controlling the group head solenoid and pump motor.
  • Optional: control flow rate of water by adding another precision controlled valve into the plumbing somewhere.
  • Some simple flows to follow in the UI to make a great espresso, even when a novice.
  • Grind adjustment suggestion based on extraction time.
  • Recipe database to store recipes. Selecting a recipe will automatically adjust machine parameters and will tell you which parameters need to be changed manually (e.g. grind size).
  • Monitor energy usage.

This of course requires some hardware, software and a careful design to make it happen. In a next post I’ll talk you through the plan in its current form. We’ll make adjustments as we go along.

Finally I’ll take this opportunity to do some maintenance on the machine, while I’m working on it anyway. It can probably use a good cleaning, descaling and it needs some minor repairs (steam wand is damaged because someone tried to clean it with an abrasive sponge instead of the designated cleaning solution and the manometer always indicates an incorrect water pressure). I’ll buy and reapply some new boiler isolation as the current layer will probably be damaged when I take it off to mount a temperature sensor inside the boiler and heat exchanger.

Leave a Reply

Your email address will not be published. Required fields are marked *