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"Tickling Miss Silvia": Mark Frauenfelder Hacks Coffee's God-Shot

Most companies aren’t interested in creating maker-friendly products, but sometimes, apparently by accident, a product comes off the assembly line that way. The Rancilio Silvia is just such a machine.

It was introduced in 1997, not as a commercial product but as a thank-you gift to importers and vendors of Rancilio’s expensive restaurant-grade espresso machines. Unsurprising, then, that the machine shares many characteristics of commercial equipment – robustness and repairability being chief among them.

When Rancilio decided to offer the Silvia for home use, the coffee hacking community quickly adopted it as a hackable platform for all kinds of experimental modifications. The folks on alt.coffee, the early hangout for espresso geeks, ran Silvia through her paces, carefully recording and reporting the data they collected. The Silvia became the most well-documented espresso maker in history thanks to its legion of hacker fans, who studied every detail of its inner workings and shared them on the Internet. They also obtained the Silvia’s schematics from Rancilio and made them available as PDF files. They began calling the machine Miss Silvia, which shows the level of affection its owners had for it. People merely get by with their affectless Mr Coffee, but for these coffee hackers there’s a real personal relationship with Miss Silvia.

Coffee geeks concluded that Silvia was a fine machine but that her main shortcoming was, as Glanville told me, poor temperature control. Like most consumer-grade machines, it uses a bimetallic thermostat. When the water is cold, the electric current travels though the thermostat to the heating element, which heats up the water. When the water gets hot enough, the thermostat clicks off. (It does this because it’s made of a strip of two layers of different metals with different rates of thermal expansion, which causes it to curve in one direction or the other, either making or breaking contact with the electrical circuit that powers the boiler.) The problem with this type of thermostat is that when it clicks off and cuts power to the heater, the heater is still very hot and will continue to heat the water. Then, when the temperature drops enough for the thermostat to click back on, the temperature will keep dropping until the heater gets hot again.

The experimenters on alt.coffee who took temperature measurements of the Silvia discovered that when the heating-element light is off (which means it’s ready to pull a shot of espresso), the temperature can vary by as much as 40 degrees. This amount of variation makes consistently good espresso a nearly impossible dream. But because the Silvia had so many other good qualities (including ease of tinkering), the alt.coffee gang decided not to abandon the machine. Instead, they compensated for the shortcoming by developing the temperature surfing technique Glanville had taught me. In early February 2001, an alt.coffee regular named Greg Scace performed a temperature analysis of the Silvia. He measured the temperature of the water as it exited the group head into the portafilter using a somewhat complicated temperature surfing method invented by Mark Prince (a.k.a. Coffeekid) called cheating (others call it tickling) Miss Silvia. Scace concluded that Coffeekid’s technique “worked like a charm”, with a temperature variation of just 1 degree, a fortyfold improvement.

In that same month, another alt.coffee member, Andy Schecter, posted that he had replaced the Silvia’s stock bimetallic thermostat with a PID temperature controller. (He was familiar with them from his work at National Institute of Standards and Technology). After programming (or tuning) the PID, he discovered that it kept the water temperature in the boiler from varying by more than a degree or two.

To the rapt readership on alt.coffee, Schecter wrote, “In my mind this is a TREMENDOUS improvement in the Silvia’s espresso-making ability.”

A month later Greg Scace became the second person to install a temperature controller in his Silvia. He was delighted with the results. He wrote, “I’m really getting off on having implemented PI control. It drove me nuts to have to toggle the hot water switch to tickle Silvia into turning on the heater, then waiting 35 seconds to pull a shot. Now I just look at the temperature readout, smile like a demented caffeine-addled malcontent, and hit the switch at my pleasure. My coffee is as good as when I was tickling Miss Silvia.”

That same day, Chris Beck reported that he’d successfully added PID control to his Silvia after consulting with Schecter about how to do it. That made three PID modders. After that, the hack moved like wildfire through alt.coffee. Soon, a number of enterprising coffee hackers were selling kits that included everything you needed to add a PID controller to your espresso machine.

I asked [Intelligentsia's Kyle]Glanville to recommend a PID kit for my Silvia, and he told me about an add-on kit that didn’t require any drilling, cutting, or soldering. It was made by a fellow named Jim Gallt from Lexington, Kentucky. I went to his site, pidkits.com, and ordered it. It cost $US280 (about half what I paid for the Silvia itself). A few days later, a shoebox-sized package arrived. Inside, I found several plastic bags containing electronic components, wiring, installation hardware, and a CD. I popped the CD into my computer and read through the instructions.

Silvia owners like to refer to Silvia as a girl, and the instructions that came with Gallt’s kit were no different. (“Lay Silvia down on her back, so that the front switches and logo are pointing straight up.”) Like many other kits sold by individuals, the instructions were clear and accessible, a far (and welcome) cry from the awful assembly instructions that come with kits imported from China. Gallt’s PID kit was lovingly made. All the cables were in a Ziploc bag, looped neatly, with the terminals prefastened to the ends. He even included a tiny tube of thermally conductive paste to apply to the thermostat.

Installing the PID controller in my Silvia was a lot of fun. After removing the cover from the machine to expose its innards, I attached a relay to an inner wall with a bolt and nut. Relays are very common in electrical circuits. Unlike a mechanical switch – such as an ordinary light switch, which requires a finger to physically flip it on or off – a relay uses electricity to turn a switch on or off. (The giant computers developed over the course of World War II used thousands of electromechanical relays to perform their calculations, and the resulting clicks reportedly sounded like a cascade of Ping-Pong balls dropping onto a hard floor.) The relay in the temperature-control system waits for a low-voltage signal to be sent from the PID controller to turn the boiler on or off.

The next step was to remove the wiring from the existing boiler thermostat and replace it with a thermocouple, which is used by the PID controller to measure the temperature of the boiler. The PID controller is basically a tiny computer with a program that measures the current temperature, calculates the difference between the current temperature and the target temperature, and measures how quickly the temperature is changing. With this information, the program figures out how to get to the set point as quickly as possible without overshooting in either direction. It sends a series of on or off voltage pulses to the relay, which then turns the boiler on or off.

When the temperature is very close to the set point, the relay will turn the boiler on for a fraction of a second at a time, making the indicator lamp blink like a Christmas tree light. The PID controller also has an LED display with two lines of information: the current temperature and the target temperature. Most alt.coffee folks say that 228 degrees (measured on the outside of the boiler; the water temperature is lower) is the sweet spot for espresso. A couple of small buttons on the PID let you adjust the set-point temperature if you feel like experimenting.

It took me about four hours total to install the PID controller system. As I later discovered, making something from a kit is a very different experience from making a chicken coop or a cigar-box guitar from scratch, a process full of trials and errors, misdrilled holes, split wood, crooked angles, nips, tucks and last-ditch workarounds. Still, I learned a lot about how the espresso machine worked, and following the how-to instructions still gave me the opportunity to use my hands and get lost in the flow of making.

Finished with the install, I put the covers back on, carried the machine into my kitchen, filled the tank with water, and turned it on. The temperature started out around 70 degrees and began to rise, silently and steadily. As it got close to 228, the boiler light began flashing, indicating that the relay was turning the boiler on and off. Unlike the electromechanical relays in old computers, this relay had no moving parts and was perfectly silent. In a few minutes the temperature hit 228. It overshot to 228.2 and then backed down to 228, never varying by more than 0.2 degrees.

I ground up some Black Cat beans, tamped them down in the portafilter, and pulled my first PID-enhanced shot. Twin rivulets of caramel espresso poured into the cup, topped with a thick layer of crema. It tasted as good as the best espresso I’d ever made. Never again would I have to deal with the hassle of temperature surfing. This one variable had been locked down for good. I lifted my demitasse cup in celebration of this small triumph. I had opened a machine, modified it, and made it mine. It felt terrific.

Adapted from Made by Hand by Mark Frauenfelder by arrangement with Portfolio, a member of Penguin Group (USA), Inc., Copyright © 2010 by Mark Frauenfelder. Buy Made By Hand today because Mark is awesome.

Illustration: Nikki Cook; Hacked Silvia image via Make:


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