amourducafe Senior Member Joined: 31 Jul 2005 Posts: 34 Location: Montreal Expertise: Pro Barista
Posted Tue Feb 28, 2012, 10:58pm Subject: How to calibrate the temperature of a Gaggia Coffee/Classic
So with the kind help of this forums' members. I've recently restored a scaled up Gaggia Coffee. I now need to run water through the group to finish the cleaning descaling process. In doing so, I'd like to seize the opportunity of evaluating the temperature of the water. What is the ideal temperature I am aiming for? Can I simply collect water in a cup and use a frothing thermometer to measure the brewing temperature?
Gaggia has some convoluted explanation in the manual about the water temperature light turning on and off six times (in six minutes) before the proper brewing temperature is attained. Any tips from Gaggia users on when the temperature is right? Is that light really that reliable?
There's no general answer to your first question, because different beans may require different temperatures in order to get optimal results. Different brewing temperatures are achived by temperature surfing.
A frothing thermometer would be to slow to actually record brewing temperature, because the temperature of the water drops fast once it's dispensed into the cup. One way of recording an approximation of brewing temperture is the styrofoam cup method. You place a fast digital thermometer at the bottom of a pre-warmed styrofoam cup and pull an empty shot of hot water. It's not 100% accurate, but it'll give you a general idea.
*** "This drink of the Satan is so delicious that it would be a shame to leave it to the infidels." (Pope Clement VIII on coffee, when he was urged to ban the beverage)
Posted Wed Feb 29, 2012, 8:40am Subject: Re: How to calibrate the temperature of a Gaggia Coffee/Classic
As NobbyR said - a regular thermometer reads too slowly. Even many digital thermocouple types read a little slow.
Also bear in mind that the distance of the styrofoam cup from the group head will make a difference as the air cools the water quickly. If you set a cup under the grouphead, or put a cup right up over the grouphead or put a small cup inside your Portafilter handle locked into the grouphead --- all three of those will give you different temp readings.
Also-Also ... Depending on when you start the pump relative to the heat cycle will make a difference. And the first second or two will be hotter and the next few seconds a little cooler and so on. AND without the resistance of the coffee puck, the pump will be pumping water out of the group much faster than an actual shot - so your temps will be much cooler if you actually fill a styrofoam cup than if you just run the pump for a second or two into the cup.
In the end ... all the measuring will do is give you a feel for how the heat cycle of the Gaggia affects the starting temp and what the general ballpark of the water temp is. But trying to match the temps you measure with the temps that people post about being the perfect temp for such and such espresso blend - that will just lead you on a merry chase to nowhere. Better to get a feel for how to make the shot temp a little hotter or a little cooler by timing the start of shot to the boiler cycle --- then use your taste to decide whether you like it a little hotter or a little cooler.
Posted Wed Feb 29, 2012, 9:05am Subject: Re: How to calibrate the temperature of a Gaggia Coffee/Classic
A few more thoughts about the temp ...
I have a Classic ... but I also have one of the plastic cased Gaggias with the same internal parts. The plastic cased Gaggia heats up quickly and is stabilized much sooner than the metal cased Gaggia.
In the Classic (or other Metal cased machines) the heat from boiler is warming up the metal case (that's how the cupwarmer on top of the machine gets warm). And it really does take quite awhile to get up to heat.
I've mounted a small thermometer on the front (I will try to take a picture later) and attached the thermocouple bead to the side of the boiler so I can watch the temp swing as the heater cycles. I have also added a little mod - I put this in back, through the vent grid so I wouldn't have to drill holes in my nice, Stainless cabinet - I added a switch that bypasses the brew thermostat so I can kick the heater on during a shot without triggering the 3-way solenoid valve the way the steam switch would. I also have a second button back there that inserts a resistance in the circuit to the pump and gives me a low pressure pre-infuse and I also use it to lower the pressure at the end of the shot (I'm a geek).
Anyway ... back to temp ... I notice that the metal cased Gaggia cools down much faster (after you turn off the power) than the plastic cased Gaggia. I have thought about insulating the boiler one of these days - that will probably be my next project/experiment.
My temp routine (I have the thermometer so I can see where the boiler is) is to start the shot with the boiler at about 104C - 108C depending on the blend and my taste that day. but I start the heater with my switch for a couple of seconds before I start the brew (the temp won't change that fast - it just gets the heater started heating up to prepare for the cool water the pump is about to put into the boiler) ... then I cycle the heater on-off-on throughout the pull. The tempo of the heat cycle depends on how fast the pull is ... if I were doing a 1oz pull in 25 seconds I would turn the heat on much less frequently (if at all) than if I were doing a 2.5 oz pull in 25 seconds. I can hold the temp very flat with practice.
NobbyR Senior Member Joined: 10 Jul 2011 Posts: 2,039 Location: Germany Expertise: I love coffee
Espresso: Poccino Opus One, Ariete Grinder: Eureka Mignon Istantaneo Vac Pot: N/A Drip: Melitta Linea Unica de Luxe Roaster: N/A
Posted Thu Mar 1, 2012, 4:17am Subject: Re: How to calibrate the temperature of a Gaggia Coffee/Classic
... In the end ... all the measuring will do is give you a feel for how the heat cycle of the Gaggia affects the starting temp and what the general ballpark of the water temp is. But trying to match the temps you measure with the temps that people post about being the perfect temp for such and such espresso blend - that will just lead you on a merry chase to nowhere. Better to get a feel for how to make the shot temp a little hotter or a little cooler by timing the start of shot to the boiler cycle --- then use your taste to decide whether you like it a little hotter or a little cooler.
shep236 Senior Member Joined: 7 Jan 2013 Posts: 10 Location: berkeley Expertise: I love coffee
Posted Wed Sep 18, 2013, 8:39pm Subject: Re: How to calibrate the temperature of a Gaggia Coffee/Classic
I think the old Coffee Gaggia Classic (w/o solenoid) that I'm trying to renovate does not produce sufficiently hot water. Measured in a variety of ways with different thermometers, the results all point to a water temperature of 140-160 F.
This temperature range is achieved after the machine has been left to heat up for more than one hour. Whether the thermometer is in a glass, receiving water directly from the brew head or through the pf seems not to matter. The styrofoam cup method produces similar results, as does the temperature taken at the steam outlet with the setting at steam (which I thought would be hotter).
I have so far searched in vain in an attempt to discover if the problem might be anywhere other than in the thermostat and, if not, if the thermostat is adjustable, and if not, is it replaceable?
Posted Wed Sep 18, 2013, 9:42pm Subject: Re: How to calibrate the temperature of a Gaggia Coffee/Classic
It is very difficult to tell water temperature measuring in a cup. First, is the machine warm with PF in place. It helps hold in heat at the group. I have tried to use a Styrofoam cup and get repeatable results. It I used an instant digital thermometer and if I preheated everything then I could get close. The temperature of 200F water falling into a cup and waiting for a thermometer to react is falling rapidly as you measure it, thus the low readings. Have everything heated to 190F - 200F, then dump the preheat water, and then immediately run the test and see the temperature. Styrofoam cup has low thermal mass and does not add or subtract much heat. See Styrofoam cup method here
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