# Gaggia Classic Brew Temperature Graph



## Krax

I thought this might be of interest to some. Having the test equipment required, I decided to log the boiler and portafilter temperatures in my classic during a 30 second shot. I wanted to see the approximate brew temperature (as measured below the puck)

The boiler temperature was measured using a calibrated thermocouple taped onto the outside of the boiler just below the thermostat and insulated from external influence.

I switched the classic on 40 minutes beforehand and flushed the grouphead beforehand to bring the boiler heater back on. I then started the shot as soon as the brew lamp went back off.

As can be seen, the portafilter temperature seems a bit too low. I can see why some recommend operating the steam switch briefly before the shot to increase the boiler temperature a couple of degrees.

It also helps justify the PID mod.


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## Jim bean

Nice one krax fitting a PID has been the best thing Ive done to my classic


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## Bigpikle

This might be a time to ask the newbie question about exactly what a PID is going to achieve on a Classic? If I'm temp surfing what does it add?


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## Jim bean

Hi bigpickle the PID controls the boiler to a set temp and holds it eg 93c

with out the PID the boiler cycles going off the blue line on kraxs graph between 84c and 98c

so it takes all the guess work out of temp surfing I tried temp surfing for a while but after fitting the PID the consistency in the coffee was excellent and would say a PID is a must upgrade on the classic

cheers james


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## charris

Krax said:


> It also helps justify the PID mod.





> Nice one krax fitting a PID has been the best thing Ive done to my classic


Agree that the PID is very useful. I have doubts though that it helps the temperature DURING a shot though.

What it does it allows you to "see" that you are in the correct temperature to start your shot (or your steaming).

By monitoring the temp you learn to your machine better i.e the classic needs a lot of time to come down to brew temp after steaming and this is not evident at all without a PID. Another observation is during the first flush (after the machine has been of on for some time) the temp drops amazingly fast (that's why the flush is needed) and then you have to wait for a minute or so to get to the correct temp. More examples like these are easily evident when you have a PID so you learn much more about your machine and at the end your process improves.

Since then graph though is about the temp during the shot I am not sure that the PID can help much.

P.S. Feel free to correct me, these are merely my observations


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## Jim bean

Totally agree with the above

a good tip I've learnt for cooling the boiler after steaming

after turning the steam switch off I hit the brew switch as normal to refill the boiler but run around 100ml of water in to a cup by the time I've cleaned up weighed out some more beans I hit the brew switch again for a few seconds

grind the beans and the brew temp is stable and ready to go again

so I can do drinks pretty much 1 after the other using this method

cheers James


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## Bigpikle

thanks all - need to investigate the PID mod I think.


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## majnu

Pid just takes the guesswork out from temp surfing, but at the end of the day if you can get great tasting espresso without one then there really isn't need to change. However for the steaming side of things the difference is night and day.


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## peterj

Jim bean said:


> Totally agree with the above
> 
> a good tip I've learnt for cooling the boiler after steaming
> 
> after turning the steam switch off I hit the brew switch as normal to refill the boiler but run around 100ml of water in to a cup by the time I've cleaned up weighed out some more beans I hit the brew switch again for a few seconds
> 
> grind the beans and the brew temp is stable and ready to go again
> 
> so I can do drinks pretty much 1 after the other using this method
> 
> cheers James


This general approach has been great for me also, I turn off the steam switch, and I dump out the steam through the wand and head until I get water..got to be a few hundred mils each time, do something else like grind etc then make the next shot. Forget pulling a shot after steaming without doing this...it's like an inferno...


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## gingerneil

All these guide posts on bringing the brew temp down are possible as a result of having a pid installed. The brew light only indicates that the temp it somewhere above whatever the thermostat is set at. It could be 90C, or it could be 140C. You really don't want to waste your lovely beans brewing at either of these temps. I think I spent about £40 on the PID - and the difference is huge. I find myself glancing at the PID display all the time - using it to drive when I brew and steam. The point above about bringing the brew temp down after steaming is an excellent tip. I never did this before I installed the PID because I just wasn't aware that I was pulling a shot with the boiler at 140C !

The effect on the steaming is huge too - it will go forever with the PID controlling the element to maintain steam. You don't get that from the stock machine. You do have to be careful you don't empty the boiler tho! (I'm not sure how long that would take, and don't really want to test it!)


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## Krax

As a follow up to the Gaggia Class Brew Temperature Graph I posted a while back, attached are two further graphs showing 1) the difference in boiler temperature stability with the PID Mod fitted and 2) the temperature during and following hitting the brew switch with the PID fitted. As previously commented by charris, the PID makes no difference to the temperature during the shot but at least the start temperature is better known. What was surprising to me is how long it takes the shower head to recover to the start temperature after a quick flush. The PID itself displays the RTD temperature as having reached and stabilised at the setpoint much quicker than this, which can be misleading. I have also noticed a slight overshoot with the PID autotuned which means the showerhead temperature drops by a further 0.5ºC after around 10 minutes standby, even though the PID display remains constant. To get a totally consistent shot temperature I have to flush after a half hour warm up and then brew in a 5 - 10 minute window thereafter. This seems a little OTT, but does seem to be reflected in the taste.

Gaggia RTD Stat Comparison.pdf

Shot temperature recovery.pdf


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