Intrashot Temperatures on Rancilio Silvia Espresso Machine


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What is Intrashot Temperature?

Optimum, repeatable extraction of espresso requires brewing water at a relatively constant temperature throughout the shot. The term "intrashot temperature" refers to the actual water temperature inside the coffee puck during extraction.

Different sources of information place the desirable temperature between 195F and 205F (90C and 96C). The "one true temperature" for extraction is an area for philosophers and theologians to debate, but most agree that it varies with bean and roast and generally lies within that range.

What is Silvia Capable Of?

Silvia devotees have long claimed that the heavy brass boiler and group, as well as the internal routing of water within the boiler, allow Silvia to maintain a very steady intrashot temperature profile.

In fact, many claim that Silvia can compete with heat exchanger machines using the E61 group when it comes to intrashot stability. This is significant, because HX machines cost many hundreds of dollars more than Silvia.

OK - So What Would the Mythbusters Say?

We have certainly not done exhaustive and conclusive testing on the Silvia (yet). But our preliminary results (see graph above) show that there is validity to the claims of remarkable intrashot temperature stability.

Understanding the Graph

The plot above shows a simulated typical 25 second extraction. The "thermofilter" curve is representative of the temperature of the water in the coffee puck, while the "group" curve represents the temperature of the water in the group, a few inches upstream, before it enters the portafilter.

In this particular extraction, the brew water began at approximately 203F (95F), then gradually rose to approximately 205F (96F). In other words, the extraction temperature was 204F, +/- 1F.

Note that the group temperature was relatively high (approx. 199F) at the beginning of this extraction. This is because the machine was fully warmed up, and had been used for steaming (followed by cooling flush) approximately 12 minutes prior to pulling this test shot. Had the group temperature been closer to a "normal" value of around 195F, it could be expected that the average extraction temperature would probably drop by one or two degrees.

(For a similar graph made on the newer V2 version of the Silvia, with its "tin can" style boiler, please click here.)

Our Test Setup

The temperature measurements on the graph above were made on our bench Silvia while under the control of a Watlow series 96 controller set to 228F (109C).

Simulated brew water temperatures were recorded using Greg Scace's Thermofilter device. Group temperatures were recorded using a 1/16" type K probe inserted through a custom Swagelok adapter fitted into the 6mm threaded socket in Silvia's group (thanks to Eric Svendson for his very valuable assistance).

Datalogging was performed by a 2-channel Omega HH506RA digital thermometer with RS-232 interface to a desktop Dell PC. Microsoft Excel was used to format and plot the resulting data.


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