Modifying the Rancilio Silvia Espresso Machine
The Rancilio Silvia is the reference home espresso machine. It enjoys tremendous popularity among espresso enthusiasts because it is one of the cheapest machines that is capable of producing high quality espresso. There are many espresso machines which are cheaper. There are many espresso machines that are better. But the Racilio Silvia is the price to performance king of espresso machines.
I love taking existing things and making them better. And the Silvia is a fine product that can be made even better with a few tweaks here and there.
Improving temperature control
One of the best features of the Silvia is the heavyweight brass boiler. Most home espresso machines use a thin aluminum boiler that is incapable of heating water to the required temperature. The brass boiler on the Silvia is more than up to the task, except there is a weak link in the design.
The temperature of the boiler is controlled by a cheap button-thermostat. As a result, the heating element is activated when the temperature gets below a certain point and turns off when the water is heated past another point. Makes sense right?
The problem is that there is enough "inertia" in the system that the temperature of the water overshoots the narrow range required for fine espresso. Then it rapidly falls below that range as the water cools to the point the heater is activated again. Then it overshoots. You get the picture. As a result, advanced Silvia users employ a "temperature surfing" technique.
The basic "temperature surfing" technique requires the user to pull a dummy shot, letting water squirt from the group head for 5 seconds. The user waits between 30 and 60 seconds (the optimal delay period is the subject of intense internet debate) before pulling the real shot. It has been found that this technique roughly results in a shot poured at correct temperature. But the surfing technique is error prone and is yet another variable that can affect consistent espresso pulls. There is a better way.
PID (aka Proportional, Integral and Derivative) controllers are industrial controllers which are capable of maintaining a temperature with some aplomb. They're complicated electronic devices but they're relatively inexpensive and quite easy to use. The user sets the target temperature on a little screen and the PID controller learns the behavior of the system (in this case your espresso boiler) and flips the heating element on and off rapidly to maintain that temperature.
One way to think about the difference between a PID controller and a regular thermostat is to imagine the boiler heater in the Silvia as a car heading towards an intersection with a stop sign. If controlled by the traditional thermostat, the car would speed right up to the stop sign and then slam on the brakes, skidding right through the intersection. Not good right? Were it controlled by a PID, the car would ease onto the brakes as it approached the sign, adding more and more brake pressure until it came to a stop right at the sign. Much better! Incidentally, PID controllers employ the "fuzzy logic" we kept hearing about in the early nineties.
How do they work in practice? When you power up a PID controlled espresso machine, the heating element is turned on continuously, at 100% duty cycle, just like on a normal machine. As the temperature gets close to the target point, the PID controller starts to flip off the heating element for longer and longer periods of time, it might run for 90% of a second, then 80%, etc. The heater duty cycle begins to taper off until the target temperature is reached. At that point, the heater might only be heating for a fraction of a second, exactly the right amount of time to maintain that correct temperature.
The rock solid temperature control that a PID controller can provide pretty much eliminates brew temperature as a variable. With a PID controller, the Silvia can maintain temperature as well as or better than many extremely high-end machines.
According to David Shomer, true nectar-of-the-gods espresso requires temperature far better than a PID mod Silvia can provide. But installing a PID controller certainly gets one a lot closer to this elusive goal.
The actual business of applying this modification to the Silvia is beyond the scope of this Hub. I've linked to a couple of resources with more information about buying or assembling your own PID kit. It's not a difficul mod and I promise you'll wish you did it sooner.
Silvia PID Resources
Maker of soup to nuts PID kits for the Silvia using your choice of controllers.
Improving the Barista
This should probably be the first bit of Silvia modding one should undertake before any of the more technical items. Making fine espresso is a very delicate process and it takes a shot pull to achieve consistent results.
There are so many espresso technique resources on the web that I won't attempt to give any specific advice here. But since this Hub mainly deals with the technical side of modding the Rancilio Silvia, I'll mention the naked portafilter, a tool that can dramatically improve one's espresso prowess.
Bottomless Portafilter (aka naked portafilter or crotchless portafilter)
A naked portafilter is simply a portafilter (the thing with a handle that holds the basket of grounds) with the bottom milled off. It allows one to look up at the basket and see exactly how the espresso is being extracted. With a naked portafilter, one can quickly diagnose issues with uneven tamping (like applying more pressure to one side of the puck), channeling (perhaps caused by undertamping) and a whole load of other technique issues.
As a bonus, the bottomless portafilter allows your espresso to arrive in your glass without touching any additional metal and this often means more crema. Plus, naked portafilters are really cheap and they require no installation at all. Once you start using a naked portafilter you won't go back.
Adjusting the pressure
Up until mid-2005, the Rancilio Silvia suffered from excessive shot pressure. Instead of the desired 8.5 - 9 bar of pressure, the Silvia poured at 11 bar or higher. This excessive pressure causes "channeling" in the espresso puck, a condition whereupon the puck of coffee develops cracks that let the water pass around the grounds rather than through them.
Around mid-2005, Rancilio changed the design of the pressure regulator on the Silvia and started to come from the factory set to pull shots at the correct pressure. These machines can be distinguished by the screw-out pressure regulator, as seen in the photo below. If you're lucky enough to own a Silvia of this newer vintage, you can tweak the pressure by adjusting this screw but most likely you're already in good shape.
If you own an older Silvia and you want to dial down your pressure, you'll have to do the traditional Silvia pressure mod. It entails disassembly of your OPV regulator and installing some washers to shim out a spring inside.