While this works for keeping the head from overheating during an idle; it reduces the efficiency of the system for keeping the head at temp during pulling shots in a row.
This may be perfect for the home user in search of precision, infrequent shots.
The heat sink idea may have one drawback. If the temperature in the HX tube drops, it may cause the boiler heater to run more and counteract the heatsink.
Sounds correct. How 'bout (getting crazy now) wrapping heater wire around the part of the tube that exits the group (re-enters the boiler) so the boiler's none the wiser?!
I also like Paul's idea of salvaging parts from a junk machine to tinker with.
Ok guys, keep the ideas coming. We'll get an elegant and cheap solution to the E61 precision-seeker. The article and referenced articles were too cool. I hadn't seen them before and I know there's a solution waiting for us.
Information on this is usually buried in old Faema tech manuals (which few people ever read) and are almost impossible to find, but E61 head temperatures are controlled three ways. In fact all flow through designed heat exchange machines are done this way:
Base pressure stat settings where one bar equals 253 degrees. Pressure stats can be more accurate than PIDs if you get one of the small ones built in Los Angeles by Little Giant. .05 bar to activate which gives a reaction range of 1 degree f. Temperature differentials between boiler and head also self regulate static head temperatures during switch cycling.
Heat exchangers have cold water injectors that can be modded to increase or decrease the thermal differential between initial extraction temperatures and saturation extraction temperatures. In the early days, you could order different tubes for the purpose. Italian roasters could specify certain tubes for there coffee blends. As you get into the nuances of heat exchangers and Italian theories of extraction, you may grow to appreciate your machine over that of twin boiler designs.
Most important for americans; a flow restrictor in the heat exchanger is inserted at the upper pipe fitting of commercial machine to regulated the static head temperature (non use). You can use a ball valve to find your own sweet spot.
If you have a pre-infused machine, you'll want the water to run a little 'crispy' in the first 5 seconds of the extraction and then drop to the desired brew temperature. E61's are designed that way. Excessive head flushing defeats the purpose. Head temperatures for these machines should NOT run under 240-245.
If head temperatures are too excessive, especially if boiler setting exceed 1.3, the flow restrictor is the best bet. Otherwise a pressure setting of about .9 would produce better results, especially with darker coffees.
As you get into the nuances of heat exchangers and Italian theories of extraction, you may grow to appreciate your machine over that of twin boiler designs.
What do you mean? I am new at all of this. Your post intrigued me. Any good sources you can point me to re: Italian theories of extraction?
I used to write for Fresh Cup and will soon be contributing to Coffee Geek. Hope to cover some of this in the next few months provided I can deflect the stones and coffee pucks I expect to get thrown my way.
Italians usually care about selling machines; the old timers that really know what goes on inside them have faded from the scene a bit in favor of trained engineers who spend most of their days trying to make super-autos not break.
The referance to heat exchange pipes and Faema's I read in an old service manual several years ago. THe E61 was invented by Vergani (I know that spelling is suspect) and revolutionised everything in espresso machines. There still isn't a better head design out there--it is the standard by which everything is measured.
The idea is that you brew at two temperatures, not one. Come in hot to elevate the puck temperaure as quickly as possible and open the cellular structure of the coffee to better accept the extraction. Do so at a reduced pressure so that that it opens the pores without flushing the oils, etc. Have the extraction pressure rise to coincide with the reduction in temperature coming from the exchanger (cold water injector) and the extraction is near perfect.
Its called thermo-compensation; all commercial machines do it, some better than others. Putting mods on pro-sumer machines that pro-s have used for years makes more sense. Simplicity in design fosters perfection in the cup.
Feama used to push the notion that their machine were so efficiant at extraction that you needed less coffee per shot. Twin boiler machines can't do this. Which is why all the fuss about tamping. If your machine is dialed, tamping is more or less redundant on pre-infused machines IMHO.
Italians tend not to write much down. You gotta give them a glass of wine and pich their brains. Besides, they don't think Americans know anything about espresso machines--kinda snobbish that way.
Welcome Micheal, I think you've just taken the "who is this guy?" record for a first post.
For the record, I have a small Isomac, E61 head, but a small 1.2 liter boiler. The heat exchanger is a straight tube running parallel to the heater, which is good, since it remains relatively stable while steaming, since it gets some heat from the heater (which runs while the steam valve is open).
When I did the head temperature measurements. I found a 6 to 7 ounce flush (after a long idle) reduces the initial temperature to brewing range (90C to 95C at the top of the puck). Of course, if one measures, a la Schomer, with a thermocouple in the basket, it takes several seconds for the puck to come up to brewing temperature from the initial 80C - 85C.
If I understand your post correctly, you're saying if one flushes less, and allows the overheated water to enter the puck, the temperature will stabilize to the right brewing range in the first 10 seconds, before the water flows, while the pressure is ramping up. I'll have to try this.
Two questions:
Doesn't the overhot water create some extra bitterness at the initial contact if one does this?
If one is pulling lots of shots in row, the head and HX water are at the right temperature from the beginning of the shot to the end (I get roughly than 1/3C variation during a shot when everything is running right). I suppose the HX water doesn't overheat very quickly, since it's circulating through the group during the time the PF is being reloaded. So I can't see how the Faema dual temperature theory would apply to a "busy machine."
By the way, according to Mark, and many members, the most impressive straight espresso performance comes from the Isomac Zaffiro, a single brew boiler, no HX, machine with an E61 head and a vapor pressure thermostat.
I used to battle the starbux techs in Seattle (10 years ago, the statutes are up) over where to best measure the temperature for setting up the machines. LM Thermo-couple (factory models) can't read traditional machines right. They were so obsessed with the gauges they never bothered to look at the coffee.
THe Italians were trying to get a standard set a few years ago as to what defined an espresso machine, the key factor being that it brew at 202 degrees give or take a touch. The idea is that you an run hot if the pressures is low, changes the extraction characteristics. If you start hot under pressure, it does mess things up a bit. When espresso machines from Italy were first responding to 'the need for endless steam, they sacrificed coffee quality for steam pressure. The flow restriction devices started showing up when boiler pressures hit 1.4.
Espresso machines work in duty cycles, like most other pieces of equipment. THe elevated group relative to the boiler is what makes the flow through heat exchanger work. It heats up at close to the same rate as the boiler. Brew a shot, the whole therm-syphon, thermo-compensation thing happens. Dump the grouonds, grind the next shot steam some milk and the twenty or so seconds that go by is enough for the thermo-syphon (think ocean thermal gradients here) to elevate the head temperature again. THe boiler temp would elevate in responce to the demand on the machine, creating the temperature diff. making the whole thing come back to balance.
If you did do non-stop shots, the balance would, indeed be off. It usually doesn't happen. you buy bigger machines according to your demand. THe factory tech manual for Marzocco discourages flushig the head beause of the demands on the boiler--thows off the temperature stability. Heat exchange machines can have the same problem, though the thermo-syphon effect (that also slows down to maintain head temp when the boiler refills) mitigate some of that.
Horizontal heat exchangers are only slightly less efficiant (compared to Pavoni/Faema/ San Marco, etc) with off vertical designs, but the syphon operation still holds. It all comes together because hot water rises into a cooling head exposed to air.
Another thing about cycle times. As steam pitchers increased in size, once very capable machines had a hard time keeping up. Espresso machine productivity actually rises (along with quality) when baristas throw away the gallon milk pitcher and go back to sub litre varieties.
The single boile Zaffiro operates the same way as a Cimbali or Spaziale system in many respects. A static boiler/head temperature setting that is reduced as cold water enters the common boiler. My Brasilia Club--not a fancy machine mind you, but it looks nice on my counter--produces a first rate shot as well. The temp controls are notoriously wide from on to off, but there is pipe that draws the hotter water from the top of the boiler, only to have it directly cooled from wter entering t about the same point. In multiple groups share the same boiler, they can't each share in the thermo-compensation effect.
Vapor pressure thermostat doesn't sound right though; a single boiler machine cannot use a pressure stat (except for piston/hydraulic machines) as the pump pressure pushe 9 plus bars. Most pressure stats operate in the 0-2.5 range. When the pump comes on, the element would shut down. the thermostat is probably the same as Brasilia/faema home units. Just a couple of Italian companies make them now.
On top of your brewing head is a nut, under which is a device called a gicluer/gicleur. Its a tiny hole (.7mm) in a brass nut that creates a pressure drop on the output side of device. Acts like an expansion valve. Ever wonder how you get 202 f water out of a boiler operating at 253 f? Every 1/10 of a bar rise equals 2 degrees f.
Oh, and temperatures are the same for machines no matter the altitude; they don't use pressure differential stats, they balance against a spring that isn't affected but athmospheric pressure.
But I think I'm wandering here. Its late.
Don't forget that the heat pre-infusion device takes up some of the hot water, so its difficult to know how long it takes for the water to cool when running it without coffee.
ljguitar Senior Member Joined: 28 Jan 2003 Posts: 2,450 Location: Cheyenne Expertise: I live coffee
Espresso: Expobar Pulsar Grinder: Mazzer Super Jolly, Solis Drip: Bunn Roaster: iRoast2
Posted Fri Jan 16, 2004, 7:54am Subject: Re: e-61 machine flushing...a note to Michael Teahan
Michael_Teahan Said:
Oh, and temperatures are the same for machines no matter the altitude; they don't use pressure differential stats, they balance against a spring that isn't affected but athmospheric pressure.
Hi Michael and thanks for 'wandering' for us. It is good to know that living at 6300ft above sea level isn't necessarily fighting substandard conditions for espresso builders (though some have indicated such). Roasts do go quickly here, and water boils much lower temp (3 minute egg becomes 6.5 minutes).
It would be interesting to know how that affects we high altitude espresso folks.
Could you please wander a bit more in a little more street vernacular about temps being the same for all machines regardless of altitude, and how should we approach the shot (we are owners of an Expobar HX)? Should we just hit the button (usual procedure) or bleed the head before pulling that first shot of the morning?
Michael_Teahan Senior Member Joined: 15 Jan 2004 Posts: 131 Location: Los Angeles Expertise: Professional
Vac Pot: Vintage for collecting only Roaster: None
Posted Fri Jan 16, 2004, 9:47am Subject: Re: e-61 machine flushing...a note to Michael Teahan
Larry,
Because the pressure stat diaphram against a spring, not ambient athmospheric pressure, it is a sealed system unaffected by altitude. Boiler temps relating to pressures are as follows:
1.0 bar = 253 1.1 bar = 255 1.2 bar = 257 1.3 bar = 259
You can get a 4 degree swing just in the p-stat differential setting. Thermo-syphon compensates for a bit of the fluctuation, however.
I honestly haven't worked with too many of the pro-sumer machines, but my guess is that they are set to Italian specs, where the ideal p-stat setting are closer to .9 bar. Head temperatures will be a bit lower than boiler temperatures but still hotter than extraction temperatures.
Most information, even in the trade, is anecdotal. Like roasters, information is guarded and foggy at best.
10 years ago it was about big boilers--which I always thought was stupid. Then it was about tampers in twelve different shapes and sizes--don't mean to mislead; I have a nice SS tamper and I like to use it cuz it keeps the counter clean. Now everyone is obsessing about temperature stability.
Espresso is like cooking; all the ingredients matter, not just the stove or the pan. Old lever machines in Naples make coffee that will make you cry, and nobody checks temperature or watches for extraction times.
You get better as you work with the machines, adapting to its particular characteristics. It comes with time. Obsessing about the guts of the machine sometimes places too much emphasis on the wrong side of the portafilter.
Yes, bleed the head in the morning, Not so much for temp as to evacuate stale water from the group. You don't cook with hot water from tap, after all.
The only time we ever tested the head temperature this way was with the Marzocco temperature portafileter, letting the portafilter rest in the head to get a read on the static temp.
Strabucks couldn't get a Brasilia they were testing to fall below 236 no matter how hard they tried--though it was a modded machine unaffected by steam pressure changes.
The temp drop through the brew cycle is small. You can try an infrared thermometer on the top of the head (where the flow through circuit resides--but you will likely get different temps at different parts of the head. Try adjusting the pressure stat first to find a range that works best with your coffee. If the pressure is too low to steam well, you can then take a look at flow restricotrs to lower head temp or a different gicleur in the head. If you remove them thay scorch the espresso pretty badly.
There was a cartoon I saw years ago that sums up the Italian process of testing equipment: The germans, when outfitting exhaust systems to their new Porsche had every kind of meter and guage plugged into every oriface to test the effect of each system as they changed it. The Italians, working on their new Maserati, would sit quietly drinking espresso and listening intently to the note of each exhaust pipe as they were mounted until the lead engineer pronounced, "That one, that one right there sounds about right."
Gotta love the Italians, its really kinda like that.
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