Rancilio Silvia – The case for Temperature Surfing and PID control

The Rancilio Silvia is fantastic. But what about this issue of temperature (in)stability? How important is it to temperature surf and how do you do it? Is a PID controller the answer? A few weeks ago, I pidded a brand new Silvia. Now I’ve gotten around to conducting some temperature tests and this is what happened.

These are the questions I was hoping to answer for myself. Hopefully there are others that will find the results helpful:

  1. How much “swing” is there in the boiler temperature?
  2. How does the temperature swing affect espresso extractions?
  3. How effective is temperature surfing in overcoming the temperature swing?
  4. How effective is a PID controller in overcoming the temperature swing?
  5. Any other benefits of fitting a PID to a Silvia?

Some notes on the experiments:

  • I only conducted these experiments once and all of them on the same near-new Silvia. As far as I can tell, it’s a typical Silvia (and I have used a few over the last year or so), and none of the results surprised me, but I am unable to draw any conclusions about the variance in the Silvia “population”. So I can’t say how different another Silvia is likely to behave. If anyone would like to add to the sample size, let me know.
  • The PID is a Watlow SD3C with steam control from MLG. Jetblack Espresso “donated” the Rancilio Silvia . It is now back on the demo bench 😦
  • For experiments with PID “disabled” I reinstated the Silvia’s temperature control via it’s brew and steam thermostats and unhooked the PID’s control of the heating element. The PID was still indicating where it would energise the element via the little light on the PID display, however the message wasn’t going anywhere. The PID is basically a fancy boiler temperature guage
  • The thermocouple is mounted at the top of the boiler. If this temperature is different from the steady state group head temperature, there will be some temperature “smoothing”. This is where the Silvia’s liberal use of brass helps. However, I did not attempt to quantify this effect. One day I will get my hands on a Scace device and do the next series of experiments. For now, it’s a matter of measuring actual top of boiler temp and taste testing the resultant espresso/latte’s.

1. How Much Temperature Swing is there in a Rancilio Silvia?

On my Silvia, I measured a 32 deg C (58 deg F) swing in the boiler temperature:

Min: 85 deg C (185 deg F)

Max: 117 deg C (243 deg F)

Procedure: I flushed the machine until the boiler element light came on and waited until the temperature “topped out”. Here is the video:

But what’s the effect of such a swing?

2. The effect of temperature swing in espresso extraction

This test was intended to show the a worst case scenario – pulling a shot at the bottom end of the boiler temperature cycle and then steaming milk after the light goes out. The results are pretty subjective, basically it came down to watching and then tasting the shot. The shot was predictabley pale and sour and the resulting latte was weak. Here it is:

3. Temperature Surfing the Rancilio Silvia

I use a reasonably consistent method of temperature surfing when I use the Silvia. I hit the brew button until the boiler element light comes on and then prepare the portafilter – grind, dose, tamp – by which time the light has gone off, then I insert the portafilter and hit the brew button. My reasoning is that this is repeatable and anything that increases consistency is a good thing when we’re trying to control all the variables that go into the espresso making process. Here is that process, but with the addition of the PID showing us the temperature as the espresso extraction proceeds. Remember the PID is NOT controlling the boiler element.

Using this method of temperature surfing, the boiler is at 116C (241F) when I hit the brew button which is arguably too high. The temperature drops to 106C (223F) by the end of the shot so the intra shot temperature swing is 10C (18F).

The resulting shot had a crema with some very dark tones and lighter tones. The shot was a little burnt/bitter.

(i) (Advanced) Temperature Surfing

The good news is we don’t have to leave it there. So long as the procedure is repeatable it can still be used. The obvious addition is a small cooling flush before brewing which should bring the boiler off its maximum temperature just enough. The other commonly employed technique is to wait a certain number of seconds after the element light goes off – but I’m usually too impatient for that technique 😉

This is what happened:

The boiler hits 116C (241F) again just as the portafilter is ready, this time however, the brew button is activated for about 2 seconds which drops the boiler temperature to 110C (230F), then the portafilter is inserted and brewing begins. By the end of brewing, the temperature is 99C (210F): a swing of 11C (20F).

The crema seems to be a more consistent reddy-brown. The shots aren’t tasted but the latte’s taste good.

The other “trick” employed is to start steaming the milk while the element light is on (as close to possible as it going off – which is a trick). This keeps the element energised which keeps the steam pressure as high as possible and the steaming operation as quick as possible. This is a lot easier with the temperature gauge in place, but in practice it works ok to start steaming about 30 to 40 seconds after hitting the steam switch.

Put all this temperature surfing stuff on top of getting everything else right – grinding, dosing, tamping etc and it’s a process. Which is why the PID controller is so popular.

5. PIDing the Rancilio Silvia

A PID controller keeps the boiler temperature at a predetermined setpoint so we don’t have to temperature surf. Fitting a Rancilio Silvia with PID is a popular modification and this video will illustrate the benefits.

Here are a couple of lattes prepared with the PID controller activated:

Things to note:

  • Silvia is at 106C when shot starts (which is the setpoint)
  • Intra shot temperature minimum is 98C
  • Intra shot temperature swing is only 8C as opposed to 10C without PID
  • While steaming milk, PID re-energises the element if the temperature gets down to 147C

Conclusions

On a standard Silvia there is enough of a temperature swing to produce the occassional sour/underextracted or bitter/overextracted shot. A simple temperature surfing method will ensure sour shots don’t happen, while a more advanced temperature surfing technique is required to ensure bitter/burnt shots are history.

It is possible to improve the steam performance of the Silvia with a relatively simple temperature surfing technique.

For all the advantages of the most elaborate temperature surfing techniques, the simple (albeit more expensive) option is to fit a PID kit. The other advantage to having a PID kit is that the temperature readout allows the barista to be more involved with the process, for example you could spend a couple of days doing temperature experiments and then writing a blog entry about it …

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19 Responses to “Rancilio Silvia – The case for Temperature Surfing and PID control”

  1. Video 2 and 3 are the same.

    Apart from that, thankyou for going to the trouble of putting this together. It was very informative 🙂

  2. Hi Phil,

    Thanks – video 3 now fixed.

  3. Hey, lot of thanks for the info. GREAT! 🙂 🙂 🙂

  4. Skyler Tanner Says:

    I keep getting the occasional reference from this blog post, though I can’t find any direct links to my site.

    I certainly don’t mind; keep up the good shots! 🙂

    Best,
    Skyler

  5. The Ledman Says:

    It’s always good to see an ANU engineering degree put to use.

    Suddenly my happiness with the machine has dropped a touch. I’ve been pouring a few seconds of water after the light goes off so that it comes back on again, and then waiting for the light to go off before I make my coffee (ie I temp cycle it once). Obviously I need to go one step further. The reason for doing this was to actually get the cup and basket warmed up. I wasn’t thinking so much about the machine itself.

    That temp swing without the PID is very surprising. I would have expected something like 5 degrees, 10 at the most. Definitely not 32.

    Ledman

  6. charliem69 Says:

    Don’t let the temp swing get you down Ledman. Remember the swing measured in this experiment is at the boiler. There is a large amount of thermal mass between the top of the boiler and shower screen at the group head – a chunk of brass in the group head – which will bring the temperature back towards the stable temperature by some degree. How much it brings it back is a good question. This chunk of brass is what sets the Silvia apart from many of it’s competitors in this price point.

    Of course knowledge is power and it’s the reason I wrote the article – knowing what you’re dealing with should give you the means to adjust your technique accordingly. I’d be interested to know whether you can taste a difference in your shots.

  7. You could get a little more control by implementing two closed loops. The first closed loop controls senses the boiler temperature, while the second closed loop senses temperature at the shower head. You’ll need to model the thermal time constant (thermal delay between the two sensors).

    Twin loop systems, along with stability, pole-zero plots and the like were worked out back in the late 1980’s. I.e., One inner and one outer control loop.

  8. Very informative. Thank you. Now I just have to save up for a PID…but I’m saving up now for a gridner. What did I get myself into?

  9. […] Temperaturkurve Silvia bin gerade auf diesen grossartigen blog gestossen, der das temperatur surfen bei der silvia mit video + text erklrt. die verwendete silvia […]

  10. Thank you so much for making the effort! I hope to make better coffee with my Silvia!

  11. I’ve always been suspicious of the high end temp in my silvia. Early on i noticed that when i ‘primed’ the shower head after the espresso making light went out, in prep to run the shot, steam and high pressure water would come out initially. As a result i figured i should run the pump until the high pressure dropped off, then put the portafilter on and run the shot… seemed to be a more consistent and better coffee as a result (but frustrating that i had to do it). Your experiment lends support to this not being ‘all in my head’. Thanks for that. But one question… at what temp does the light come on if left to its own devices ie, not running in cold water to get the temp down to the light being activated.

  12. Very informative, was interested to find out if the PID was worth it and it appears that it is especially if you aren’t a Barista and want a great coffee…Thanks for your time in doing this.

  13. Thanks for posting all this info. If nothing else I ended up choosing the Silvia because of all the information from people like you that have been using them.

  14. […] meg ikke: Silvia lager veldig god kaffe, men den beste kaffen får du ikke før du mestrer såkalt temp-surfing. Utfordringen med enkle hjemmemaskiner som har bare én kjele, én termostat, og ikke måler […]

  15. Awesome!!!!! Thanks for all the hard work mate.

  16. Very useful information mate !

    Cheers !

  17. Thanks for a nicely put blog. I own a V3 version and wonder if the same methods hold true for the latest and greatest. Also should I install the PID myself (i.e. is it relatively simple process), or get it installed by vendor? Thanks.

  18. Hi, Great blog. One question though, regarding the last video: after you have brewed the espresso, using the PID to keep a steady temp between (98-106 C), it rushes up to >147C, why is that? Do you switch the PID off ( i can’t see it in the video) or does it magically know that you are about to steam milk and therefore heats up to maximum 147C. By the way, is >147 C the best temperature for steaming milk and not the same 106C as for the espresso?

    • charliem69 Says:

      The PID handles steam temperature as well as brew temperature. When you flick the steam switch on, the PID takes the boiler to 140 degrees or so. The more steam the better. Ideally with a single boiler like the Silvia, steam temp is over 135 degrees.

      charlie

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