I recently purchased a Giotto Premium and so far have had a hard time getting the temperature profiles right. I just bought Eric's thermometer adapter (which is simply awesome by the way...). I calibrated it and installed it last night and have been playing around with it.

My system is set up at 1.2 bar boiler pressure. The steady state grouphead temp is a whopping 220 degrees.

I followed some of the other posts in the forum as well as the docs on Eric's FTP site. I started by flushing the GH temp down to 185 and then letting it bounce back to 198 before pulling the shot. It probably takes about 10-12 ounces of flush to get it down to 185. Having seen the profiles that were published, I was expecting it to take about 60-90 seconds to pop back up to shot pulling temp. On my machine it took just over 200 seconds. When I pulled the shot it came out extremely bitter. My theory is that the water in the HX became superheated during the time it took the GH temp to rise back up and ended up scorching the coffee. Is this possible? I suspect the group head can only move the temperature of the incoming water so much even if it starts at the right temp.

To shorten the wait interval, I flushed the next shot down to 190 and it took it less time to come back up to temp. I didn't measure the exact time, but I would guess ~120 seconds. The shot tasted much better, but still wasn't quite right. I'm jacked up on caffeine now, so I can only run so many experiments per day...

When doing the flush, wait, brew method, is there a target time frame for getting the grouphead up to temperature? It seems like the ideal would be for the water in the HX loop to come up to approximately the desired brew temperature and have that coincide with the GH temp. Does anyone know how long that is? Has anyone tracked the temp of the water in the HX loop versus the GH?

Why does my machine take so much longer to recover from 185 than the other machines that have been posted? Do I have some kind of flow restrictor in the HX loop?

Kenja,
That's too low for a cooling flush for the giotto. My gh also hovers around 220' at rest, which is normal. You only need to flush down to 201' (or 205' or so), wait 10 seconds or so, and pull your shot. 185 is going to cool the gh too much and I bet the temperature is diving down during your shot because you wasted the heat capacity of the gh to stabilize your shot temp. And when you're watching the temp gauge, waiting for it to come back up - that's not the water temperature, that's the air temp in the gh, and when you pull your shot, it will change wildly once the hx water hits it.

Watch the temp on your temp gauge during the shot to see what is going on. Play around with the rebound time and cooling temp, but I normally cool to 205' ish and have a 10 second rebound and pull - or cool to 201', 20 sec-ish rebound and pull. Experiment around with it, but either way, the whole pull is going to be around 205 (for the 205, 10 sec) or 201 (201, 20sec), depending on the cooling flush temp and rebound time. Different blends will like different temps, ymmv.

Have fun!
Geoff

Thanks for the feedback. Are you using the same gh themometer setup that I am? I'll give that a try tomorrow morning. It sounds like your using more of a flush 'n go approach with minimal recovery time.

I am still curious why it seems to behave differently than the other E61 machines that have been discussed in the forums.

kenja wrote:I am still curious why it seems to behave differently than the other E61 machines that have been discussed in the forums.

They all behave a bit differently, and Geoff's recommendations match my recollection of testing the Giotto Premium. Big flushes, fast recovery; the Expobars run even hotter. Eric provides an excellent "what and why" in Theory behind flushing an E61 HX machine.

It might be worthwhile taking a breath, stepping back and remembering that the purpose of Eric's device is to allow you to repeat your best shots, whatever the reading that your thermometer gives you. The thread "Errors in Temperature and Pressure Measurement" gives you some idea that the absolute temperature that your thermogadget is displaying is likely to vary fairly considerably from the actual value. It's quite possible that your readings are as much as 8F different from other people's readings!

After all, surely the goal is espresso that tastes good, not espresso that's brewed at a particular temperature?

Cheers,

Luca

My system is set up at 1.2 bar boiler pressure. The steady state grouphead temp is a whopping 220 degrees.

Yikes ! and Ouch !

I just turned Anita's pstat up quite a bit in an attempt to simulate your 220 F grouphead temperature and, as it takes this climb in temperature a while to stabilize, I'll post a flush graph and a shot graph later on.

My first thought is that you should give a call to your machine vendor and ask whether or not a thermosyphon restrictor is installed in your Giotto. Based on your temps and the fact that the Vibiemme and Giotto share the same boiler, I would say you do not have a thermosyphon restrictor in your machine. But, based on the time it took you to recover to 198, that has me thinking.

My second thought is that you MIGHT do yourself a big favor and turn the pstat down such that it reads 1.0 bar max. or take it to 1.10 bar first. The difference you may notice in steaming capability may not even be readily apparent. Furthermore, and to echo what Luca said, I measured an 8% difference between the machine boiler pressure gage and a very accurate 0-30 psi gage.

The little digital thermometer you received hopefully had a tag on it and, if I remember correctly, it read 211.5 when surrounded with steam at 211.7. If yours did not have a tag, then it was the one that fell off but the same readings apply. The very tip of your thermometer should extend 3/8" past the end of the threads.

With the machine fully warmed up and simply idle for at least an hour, observe the difference in grouphead temperature simply by removing or installing an empty portafilter.

I tried the 201 flush with a 20 sec recovery and the result was pretty bitter. I then tried a true flush-n-go down to 198 and then another one to 200. Neither one was particularly satisfying, but was neither clearly bitter or sour. My wife seemed to like the 198 better than the 200 in a heads up taste test, but I couldn't pick a clear winner. The flavors were very muddled and not as clearly defined as they normally would be. I'd say the shots tasted similar to my old machine when I had too fine of a grind and a slow extraction. These shots were right about on target, though, at ~25 seconds for 2 oz.

I've seen conflicting reports on the temperature variation between the thermometer and the PF brew temp. I realize the thermometer doesn't give you a real picture of what's going on, but on a flush-n-go, do you think I should I be shooting higher or lower?

I'll try lowering the pressure and see how that works. I bought the machine second hand, so I don't know who to ask about the restrictor.

I'm using my own roast which is tiring me out... My IRoast is very busy these days with all the experimentation. Maybe I should buy a couple pounds of Stumptown until I get this dialed in.

Kenja

Ken -

I bought the machine second hand, so I don't know who to ask about the restrictor.

Ah ha!

I BELIEVE that your machine is "scaled up" on the heat exchanger surfaces and likely others. That is why the recovery time is so long. Take a look at what Anita did in my next post (maybe in a while) - she is very clean - I just did a boiler/hx inspection. I set the pstat to ~1.51 bar (as read on the machine's gage) to produce a grouphead temp of 219.5 F.

After all, what's a half degree amoungst friends?

I suppose it is possible. The guy only used it for three months in Portland which has soft water. It seems like a long shot.

Ken

Well, here are the flush and shot graphs as promised - below is the flush and shot together.



Here is a magnified view of the shot profile.



Yes, three months and the machine should be very clean but here is another test - see how long it takes the machine to reach that 220 F in the morning. A typical time would be 60 minutes.

I find it both interesting and expected that we take about the same amount of flushing water (11.5 oz) to reach essentially the same temperature (185). After all, the machines have the same grouphead but all else is quite different and it shows in the results. So, what may be reasonable practice on one machine may not be on another which sure is pretty logical.