# Filling the boiler and making multiple drinks on a Gaggia



## fatboyslim (Sep 29, 2011)

Since the Gaggia Classic has been around for a long time and is basically the benchmark entry level espresso machine, people must have obviously found the best way to get thermal stability and optimum steam pressure from this great little machine.

So I have two questions. I know there are ways to manually fill the boiler or at least add more water to make a shot without needing to refill and just wondered what peoples tricks and tips are for this.

Also I've found that if I make two flat whites in a row on my Baby Class, there will be a noticeable taste difference between the two.

So what is the best way to ensure thermal stability when brewing shots and also how do you maximize steam pressure?

Appreciate peoples tips and tricks


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## maarten_booij (Jan 28, 2011)

Hi fatboyslim!

I know where you are coming from. I have tried many things to get the right temp and steam in the boiler just to steam enough milk for 2 cups at once. What I do is fairly straight forward.

I let the machine warm up for 20-30 minutes in steam mode. Right before I want to steam i purge the steam wand for about 8 seconds. After closing the steam valve, fill up the boiler by turning on the brew switch, but immediately when the sound of the pump changed switch it off (to prevent damage to the pump). The boiler light will have turned off, so the heater elements are working. Wait a couple of seconds and start steaming the milk. Do not wait until the boiler light is on again, since the heater elements will be switched off.

When doing this I always have enough steam to for 2 cups of milk in one go.

For the right brewing temp, I just purge the head long enough for the brew light to switch off. I wait until the brew light switches back on again and immediately start brewing the shot. But don't put the portafilter in the head already while waiting for the light to turn on, since your coffee will taste burnt.

Doing this gives me a consistent taste. Mind that a naked portafilter helps quite a lot with consistent taste, since a temperature difference in a normal portafilter might influence the taste as well (if it was quite cold, my espresso would taste very sour)


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## fatboyslim (Sep 29, 2011)

Clearly a very experienced Gaggiaist









Thanks for those tips. I'll try them out.

What about if you are making two flat whites using double shots?

Would you make 2 doubles (one after another) then steam the milk for 2 flat whites at once?


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## jimbow (Oct 13, 2011)

If you want to overfill the boiler I remember reading that this is possible by running hot water through the steam wand. The steam pipe is further up the boiler than the brew water outlet so selecting the steam function, opening the steam wand and running the pump will allow more water to fill the boiler.

I think this is one of the reasons that the Gaggia descaling instructions specify running the solution mostly through the steam wand - to overfill the boiler so that the scaling solution comes above the scale line (where the water line normally is) within the boiler.

To be honest though I am not sure whether this would be much use for the purposes of temperature stability within the shot. The Gaggia's boiler design means that fresh, cold water enters the boiler at the bottom and as it is heated, rises to the top where it exits to the group head or the steam wand. If the boiler was overfilled, then the hottest water would probably be above the outlet to the group head.

I used to run about 3 flOz through the group head or enough water to make the thermostat kick in (whichever happened sooner). Then, once the boiler was up to temperature, and the temperature ready light switched on, I would wait a further few seconds for the water to reach temperature (the thermostat is on the outside of the boiler).

Steaming for prolonged periods on single boiler dual use machines is tricky not so much because of the size of the boiler but because they are thermostatically controlled. On machines with dedicated steam boilers a presurestat is used to control the heating element so that there is a constant supply of steam pressure even during use. As described above, with the Gaggia, it is possible to fool the thermostat into keeping the element on during steaming by starting to steam *before* it switches off and the temperature ready light comes on.


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## brun (Dec 26, 2011)

jimbow said:


> I used to run about 3 flOz through the group head or enough water to make the thermostat kick in (whichever happened sooner). Then, once the boiler was up to temperature, and the temperature ready light switched on, I would wait a further few seconds for the water to reach temperature (the thermostat is on the outside of the boiler).


thanks, ill give this a go when using mine


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## maarten_booij (Jan 28, 2011)

fatboyslim said:


> What about if you are making two flat whites using double shots?
> 
> Would you make 2 doubles (one after another) then steam the milk for 2 flat whites at once?


I actually never make 2 flat whites, and I think it is pretty hard to get consistency in that with a (small single boiler) gaggia classic. I prefer to make the milk first, since it takes quite some time for the boiler to warm up to steam temp from brewing temp, while cooling down is quicker (plus when brewing after milk you will have fresh perfect crema for latte-art).

If you want to make 2 flat whites, I would probably have two separate pitchers of milk, steam them both, and afterwards pull the shots of espresso. I have never done or tried this so it is only a theory in my mind, could be very different in the real world (although making coffee can be compared to a science, it is just as much an art, as common sense doesn't always give you the best taste).


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## onemac (Dec 15, 2011)

maarten_booij said:


> For the right brewing temp, I just purge the head long enough for the brew light to switch off. I wait until the brew light switches back on again and immediately start brewing the shot. *But don't put the portafilter in the head already while waiting for the light to turn on, since your coffee will taste burnt*.


When I run 3oz through the brewhead before brewing my shot, in the time it takes me to empty the glass and dry it, the brew light is back on before I get the portafilter located and the glass on the tray. Do you think I've left it too long and the temperature is not quite up there or do you think the timing is about right? Sometimes I locate the portafilter before drying the glass so knowing this may affect the taste is a great help. Thanks.

Al


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## maarten_booij (Jan 28, 2011)

onemac said:


> When I run 3oz through the brewhead before brewing my shot, in the time it takes me to empty the glass and dry it, the brew light is back on before I get the portafilter located and the glass on the tray. Do you think I've left it too long and the temperature is not quite up there or do you think the timing is about right?


It really depends on the taste you prefer and the type of coffee you use. Some coffees are better at 96, some at 94, and without PID it is very hard to determine the temp exactly. I usually don't bother drying the cup after purging. I just throw the water in the sink and brew the shot in the wet cup. Just try it...if it makes a difference in the taste of your shot (either negative or positive) you can adjust your method to that. Otherwise you can also try to purge in a different cup, and have another pre-heated cup at the ready.


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## onemac (Dec 15, 2011)

Thanks Maarten. It's just another variable I can dismiss in the quest. Had a hard time dialling in the Lusty Glaze today and most of the shots tasted burnt - you might have hit on the reason.

Al


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## jimbow (Oct 13, 2011)

The main reason for temperature surfing like this is to force the boiler to return to a consistent temperature. Although a temperature around 92-94 (depending upon the coffee) would be ideal, the main thing is consistency. I found with my Gaggia it was very difficult to get the water too hot but it could be too cold (at the bottom of the thermostat temperature swing). Of course, if the grounds are subjected to heat prior to brewing then that could impact the flavour as you suggest.

Could the flavour you are experiencing be bitterness? If so, try cutting the shot a bit shorter if it is blonding and/or perhaps grinding coarser. What brew ratio are you using and how long is the pour?


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## fatboyslim (Sep 29, 2011)

I believe there have been answers as to why this is not so easy already mentioned here but I forget them; after I get my Classic up and running with the PID I really want to mod it to pre-heat the water entering the boiler.

Several ways I can think to do this is:

1) to gently preheat water before putting it in the water tank (by gently I mean something like 30 degrees? just to avoid big cooldowns as the boiler empties)

2) To attach a small chamber from the pump and before the boiler which takes in radiant heat from the boiler, preheating brew water (saw some guy had successfully managed this on another coffee forum)

3) Greatly increasing the tube length from the pump to the boiler using conductive tubing which would warm up using radiant heat from boiler (could be coiled around the boiler)

Any thoughts on this? Just trying to see if any of these ideas are feasible and also trying to save money by not buying a hx machine


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## jimbow (Oct 13, 2011)

I remember reading a number of threads on this. The second idea is sometimes used on higher-end double boiler machines where the brew water is heated prior to entering the brew boiler via heat exchange inside the steam boiler. In a single boiler machine like the Gaggia a thermoblock could be used in place of the heat exchanger and should yield similar results. I saw a thread where someone had done just this; casting an aluminium thermoblock which they then attached to the side of the boiler so that it was passively heated by conduction from the boiler and the brew water was gradually preheated to the boiler temperature on its way to the boiler. The results recorded looked very encouraging indeed.

I would advise against the first idea as heating the water before the pump could change the density of the water which could in turn affect the operation of the pump and create inconsistent/incorrect pressures.


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## maarten_booij (Jan 28, 2011)

Yeah, I have seen all 3 ideas on other forums. The guy who managed to cast an aluminium heat exchanger had many (many!) problems and spend countless hours to prevent it from leaking (there is minimum 9 bars on there!). Preheating water in the water tank will indeed be bad for your pump, although 30 degrees wouldn't be too bad I guess, although I highly doubt if an increase of

I was thinking myself of making option 3. I have seen a guy on another forum who managed to extend the tubing with copper pipes, winding it around the boiler as to preheat the water coming in. I have even been thinking of putting lint-heaters / rope heaters around some of the tubing. The problem with these options are that the OPV is directly connected to the boiler, which means if you extend the tubing before the OPV, some of your pre-heated water is diverted into your tank which heats up the water in the tank, which is bad for your pump. The only option I see is to open the current OPV fully, and putting a second after-market OPV in with copper tubing in between. This way the water coming into the boiler is raised, diverted water by the first OPV will not be pre-heated and you still have proper pressure control.

To sum up: This is very complicated and hard to get waterproof I think. So I rather work a couple of extra hours so I will have saved enough money to buy a rocket / expo bar in a while


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## fatboyslim (Sep 29, 2011)

Why not just place new preheat tubing after the OPV? Couldn't the tube from OPV to water tank be diverted to drip tray?

I am also thinking this is the best solution if we can work around a few problems.

I'm about to become a student again so my future budget is non-existent. It will be all about modding what I have


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## maarten_booij (Jan 28, 2011)

Since the OPV is directly bolted on the boiler, there is no tubing to be replaced by new preheat tubing. Of course the diverter tube from the OPV can be diverted to the drip tray. Quite interesting actually







You are getting me excited again


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## maarten_booij (Jan 28, 2011)

Does anybody know if the OPV is still reliable under high temps (90 degrees)?


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## fatboyslim (Sep 29, 2011)

Maarten or anyone, could you explain a bit more about how the OPV and solenoid works so I can try and think of a way round it?

I have a spare solenoid but is it possible to rig it up not attached to the boiler? If so where would you put it in relation to a preheat chamber or tube?

I definitely think this is worth while thinking about since even with a PID I'm getting brew temperature fluctuations of about 5 degrees.

Definitely need to preheat brew water somehow.


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## maarten_booij (Jan 28, 2011)

Solenoid is not important for your goals. OPV is. I'm not totally sure about the precise inner technical workings of the OPV, but I do know the function. The OPV is connected between the pump and the boiler. The pump is working at about 15 bar pressure, but the ideal pressure for espresso is about 9 bars. The OPV (over pressure valve) diverts enough pressure by diverting water back into the water tank so that the pressure going to the boiler (and so to the group head) is the set pressure. You can change this set pressure by adjusting the screw inside the OPV.

I think it is possible to have an OPV which is not directly connected to the boiler, but with the gaggia classic it seems (imo) very difficult since it is bolted straight on and so part of the sealing of the water system. That's why I thought about setting the standard OPV of the classic on max pressure (15 bar) so it is not functioning as an OPV anymore, and put a second after-market, in-line, OPV between the standard OPV and the pump, setting that pressure to 9 bars. You could then put a pre-heating system (either thermo-block or active heating element) between the after-market OPV and the standard OPV.

For more info on OPV's check: http://coffeetime.wikidot.com/opv-over-pressure-valve


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## fatboyslim (Sep 29, 2011)

Thanks for that info.

If you were to add a preheat chamber or tube before the OPV that could produce water at a constant temperature, then couldn't you adjust the OPV to still produce 9 bar pressure at this new water temperature?

If I play around with this, what are the signs of espresso being extracted at too high or low a pressure?


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## jimbow (Oct 13, 2011)

The vibe pump in espresso machines produce fluctuating pressure profiles (due to the vibratory nature of the pump) up to 15 bar. The average pressure the pump is outputting is probably much less. One of the functions of the OPV is to effectively level out the upper fluctuations so as not to exceed 9 bar.

If the brew water is coming through at too high a pressure I expect it would overcome the resistance you have created in the filter basket (through appropriate combinations of dose, grind and tamp pressure) too easily and the pour will be too fast. Of course you could work around this by creating greater resistance in the basket but that would lead to more pressure within the basket and probably increase the rate of extraction.

On the other hand, if the brew water is coming through at too low a pressure I would expect the resistance in the basket would be too great for it to overcome and choke the machine. Lowering the resistance to compensate would restore the flow but lower the rate of extraction due to lower pressure in the basket and any changes made to lower the resistance. If the pressure is too low you might also notice less crema produced.


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## maarten_booij (Jan 28, 2011)

fatboyslim said:


> If you were to add a preheat chamber or tube before the OPV that could produce water at a constant temperature, then couldn't you adjust the OPV to still produce 9 bar pressure at this new water temperature?


Yeah, you could, but that creates the problem that preheated water will be diverted by the OPV into the water tank, effectively heating the water that is going into your pump, which can cause damage to the pump. That's why a different OPV is needed before the pre-heating chamber/tubing so that water that is diverted to the water tank is still cold.


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