Posted Fri Dec 27, 2013, 10:06pm Subject: Expobar Office Lever (thermosyphon restrictor and cooling flush)
I just bought an Expobar Office Lever. WLL says they now install a thermosyphon restrictor on all new units (basically a small penny sized copper disk with a small hole). I think they have done this for almost 2 years now? They claim a brewhead temp of 200 degrees using this device with the restrictor in place. I heard it was running at about 215 before they made this change?
My question: do I still need to do a cooling flush if they are correct at saying the machine now idles at a stable 200 degrees? If you think I still need to flush, what would be the proper routine with a hot machine (15-30 minutes after start-up, or idling for an hour or so.) I would understand if it needed a flush before the first shot, but what if I am pulling 3-4 shots in a row, back-to-back, do I need to flush before each new shot? What would be the flush and wait time? What would be better flush-and-wait, or flush-and-go? Any other ideas on flushing with this machine?
Also. If there is a need to flush would Eric's E61 thermometer be a good idea, and does anyone know if this device voids the warranty on espresso machines?
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 8,137 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Vene. A1, La Cimbali M32 Grinder: Azkoyen Capriccio, Major Vac Pot: 40s era Silex Drip: Msl. Com. brewers Roaster: gave it a try, decided no
Posted Sat Dec 28, 2013, 6:45am Subject: Re: Expobar Office Lever (thermosyphon restrictor and cooling flush)
Yes, you still need to flush, the restrictor does nothing to alter the HX brew system. The HX tube, becomes the same temp as your boiler when the machine sits for a while. Thus, the water in the HX becomes the same temp as the steam boiler. Well you still need to flush unless you like brewing at steam temp water and scalding your grounds.
You still need to flush ANY machine between EVERY shot, to clear the spent grounds from the brew group, so while you are at it, just make sure you did not wait too long between shots and make sure you are not over temp, you have to flush ANYWAY!
Learning your machine will take time, pretty soon, you will be working and not even thinking about the tech side of things but only by using your machine will you become used to the routine of your machine, every machine is different.
It may only take 5 minutes for the water in the HX system to become over temp, possibly less or more, only use will tell you.
Do you even know what over heated water looks like? Have you ever seen a flush on a HX when it is needed? Check out the short video I did on my machine to show this. You need to do a cleaning flush between EVERY shot, don't forget that!
jonr Senior Member Joined: 25 Jun 2013 Posts: 315 Location: Americas Expertise: I love coffee
Posted Sat Dec 28, 2013, 7:25am Subject: Re: Expobar Office Lever (thermosyphon restrictor and cooling flush)
You (and most people) would benefit from a thermometer that sits just above the coffee and measures brew temperature for every shot. I ran like this for a long time, until I really understood how conditions and procedures influenced brew temp.
There's a proper temperature range (about 3F - 4F) for any given bean or blend. You flush to get the brew water into that range. The ideal temperature range for all coffees is between 196F and 208F. The majority of coffees prefer something around 199F or 200F, with an acceptable "error bar" of around plus or minus 1-1/2F (plus or minus 1-1/2F from "on the money" is a 3F range ... get it?); with some coffees more tolerant to temp variation than others.
The Office's group (which includes the group head and some other stuff) is an E-61 clone, employing the principle of thermosyphonic convection to stabilize and control its temperature. If the brew water is slightly too hot or too cool, the massive group will transfer or absorb heat energy and help correct it. But there's only so much a stabilized group can do. You have to at least get close.
As Wayne explained the HX reservoir sits inside the boiler; and eventually the water in the HX will equilibrate to the same temperature as the boiler. When brew water is pumped from the HX to the group, cool new water enters the HX, mixes with what remains. That's how the cooling flush works to temp the brew water.
But pump enough water and eventually the water in the HX becomes too cool.
If the machine's idled for a long time, you need to do a longer flush than if it's only idled briefly. If the machine is being used to draw a number of shots in quick succession, the water in the HX may become too cool and you may have to wait until it's sat long enough to "recover."
It may sound complicated, and in truth, it takes practice to get right.
However, the most difficult part is training yourself how to "dial in" the proper temperature by recognizing what too hot, too cold and "just right" taste like. By the time you've learned to balance the bitters (too hot) and sours (too cold) to get to the best balance, you'll have all the control of the machine you need to nail the temp every time.
Perhaps the hardest thing to develop is confidence. Remember that if it doesn't taste too sour or too bitter -- it isn't.
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