Rancilio Silvia brew head temperature drop during the extraction

[cajun_brew]

A few weeks ago I installed a thermocouple to the top of Silvia's boiler wedged in the small brace that holds the brew thermostat in place. Wanting to see how the brew temp at the top of the boiler corresponded to the brew temp at the shower screen, I drilled a hole in a single basket and snaked a separate k-type probe up in the basket close to the shower screen. While reverse temp surfing (temp dropping), I was able to see about a 10 degree C drop from top of boiler to temp in the basket (no coffee). So I've been hitting the brew switch at around 104 C (top of boiler) and this should start the shot at around 94 C.

Question? How much of a temp drop can be expected through out the shot?
Should I hit the steam switch while brewing? Will this take the temp too high during the shot?

If I brew without the boiler active I get a very large drop in top of boiler temp maybe 10 degrees or more. I don't think the temp in the basket is dropping that much is it? It doesn't taste like it drops that much.
If I brew with the boiler active the temp(top of boiler) doesn't drop much at all but it taste like the temp might be getting too high.

I'm kind of new to the taste of espresso, only been drinking straight shots for 4 months or so.

Or maybe I should try temp surfing up and see what I get.

Any thoughts?
Thanks Tim

[AndyS]

So I've been hitting the brew switch at around 104 C (top of boiler) and this should start the shot at around 94 C.

Question? How much of a temp drop can be expected through out the shot?
Should I hit the steam switch while brewing?? Will this take the temp too high during the shot?

Most people run the boiler at 108-109C to get ~94C brew water temp. Generally the brew water temperature drops 1-2C during the shot, even though the boiler temperature drops a lot more. Brewing with the boiler full on during the shot seems to raise the temperature in the second half of the shot. It can be a pain if you're not careful because the temp can go way high after the shot is over.

[bobroseman]

When taking temperatures and most particularly, when comparing temperatures, be sure to take into account the possible measuring errors. Remember that ANSI Standard MC 96.1 establishes the tolerance value of a K-junction probe as being ± 4 deg F (2.2 deg C) measured at 0 deg C . At 95 deg C the tolerance is likely to be larger. This error is independent of the specified error of the thermometer.

One can establish with reasonable accuracy the errors for a particular thermometer/probe combination by measuring rapidly boiling water. However, in my experience because of impurities in the water and imperfections in most pots, water can measure different temperatures at various points in the pot. Additionally, water temps can vary over 10 degrees while the water appears to boil rapidly.

One must also know the exact theoretical temperature of boiling water at the test locale. This means knowing the pressure altitude at the time of the test. Alternatively one can use the barometric sea level pressure and the known altitude of the site above sea level. The mineral content of the water will affect the actual boiling point of the water. (If you wish to be more accurate boil distilled water.)

Finally, bear in mind that random errors such as a toggling least significant bit in the thermometer's analog to digital converter or thermal noise can add a random error to the systematic errors described above.

Bottom line is that there can be fairly large discrepancies between 2 thermometers due to inherent errors. The best approach is to calibrate both thermometers in boiling water at the same time. Even then, realize that the measurements will only be approximate.

Bob

[cajun_brew]

Thanks for the responses

Generally the brew water temperature drops 1-2C during the shot, even though the boiler temperature drops a lot more.

This is just what I was looking for

Bottom line is that there can be fairly large discrepancies between 2 thermometers due to inherent errors. The best approach is to calibrate both thermometers in boiling water at the same time. Even then, realize that the measurements will only be approximate.

When it comes down too it I guess taste has to be the final "tweaker"