Posted Wed Sep 22, 2004, 5:15pm Subject: Help! Shots bitter with new Expobar
I just received my refurbished Expobar Pulser today from WLL. After setting it up and letting it warm up for an hour, I then did a 8oz cooling flush to cool down the HX and made my first shot. I immediately noticed a bitter taste. I thought maybe I didn't flush it long enough, so I made another and it was the same. I tested the temperature using the styrofoam cup test with a calibrated digital thermometer. The temp was reading 210 degrees even after a 8oz flush. I figured the pressurestat was set too high so I tested it using this method. "Cheap pressure gauge!" The boiler pressure ended up being 1.2 bar. I then lowered the pressurestat to 0.96. However, I am still getting 207 temps even after flushing the HX. What could be wrong?
I knew I saw this earlier. Took me a while to find it. The table quoted below correlates pressure to the fluid temperature. This is RELATED to the brewing pressure but ther are other variables (such as ambient temp, brew path length and material, etc.. Looks from your original post like you may want to try lowering the boiler pressure again (the chap below is running at 0.8 bar).
At a boiler pressure of 1.3 Bar your boiler temp is about 125 C or 256 F , seems to me plenty hot enough. For your information I have added a pressure / temp list based on the "steam tables"
Perhaps you need to have your pressure gauge checked, I keep my machine, a two piston Futurmat Rimini, at 0.8 bar. this pressure gives me a perfect brewing temperature. Remember, no matter how high the pressure, your machine should still preheat for at least 30 minutes before use.
jrtATL Senior Member Joined: 20 Feb 2004 Posts: 1,035 Location: Austin TX Expertise: I love coffee
Espresso: Expobar Office Control Grinder: Mazzer Jolly; Cunill... Drip: Melitta Clarity Roaster: Drum on a Weber grill; HG/DB
Posted Wed Sep 22, 2004, 7:35pm Subject: Re: Help! Shots bitter with new Expobar
Hi. If you are using a gauge like the one mentioned in the thread you reference, don't place too much stock in the numbers listed on the gauge. Just because the gauge says "1.2" doesn't mean your pressure is actually 1.2. Gauges, in my experience, can make precise measurements, but they do not always communicate the measurements accurately.
For example, the gauge I installed in my expobar reads 0.3 when the machine is completely cool and I have let out all pressure. I know that my gauge results are skewed by 0.3. So, if I want a setting of 1.0, I will set my machine so that my gauge reads 1.3.
All of this to say that a boiler pressure gauge is great to tell you the difference between your starting and ending point of the adjustment, it just may not tell you exactly wht the "true" pressure is.
To get you boiler where you want it, you will need to spend an hour or two playing around with it. Jim Schulman (another_jim) has posted a great article on how to adjust your pstat without using a gauge. I followed his advice while using a gauge, and it worked like a champ. Basically, you flush the group, and then take a styrofoam cup reading to see what your temp is. Then adjust your pstat a little and wait for the boiler to cycle a time or two. Then, take another styro reading. Keep working your way down until you get it where you want it.
I widdled my brew temp down to 89C the other day (looking the the Italian Institute's 88C recommendation).
One final thought (especially since I have rambled on...), double check your styro cup method. Make sure that your thermometer is not touching any part of the group while you run the test. That would definitely skew the temp up.
Good luck, and keep us posted.
"I've appeared before every court in the state. Often as a lawyer." - Lionel Hutz, Esq.
Posted Wed Sep 22, 2004, 8:04pm Subject: Re: Help! Shots bitter with new Expobar
Well, I've managed to get the temp down to 202 after flushing. However, the steam is now pretty weak (it takes 2mins10sec to heat 10oz of 40degree water to 150 degrees) and the boiler pressure is now registering at 0.48 bars (7psi). I'm trying to figure out possible sources of error, but I have yet to find any. The thermometer reads 212 exactly when placed in boiling water. I've compared the tire pressure gauge to two others I have, including a digital one, and it is within 0.5psi of the others. I think I'll give WLL a call tomorrow and see if I can get this figured out. Thanks for all the help.
Posted Wed Sep 22, 2004, 8:58pm Subject: Re: Help! Shots bitter with new Expobar
The implication of both your pressure and temp measurements being correct is that your heat exchanger is some how transferring more heat than the designers intended.. One possible explanation for this phenomena, is that the brew water is spending more time in the heat exchanger than it should. Another is that there is less water in the HX to heat. Have you done a water debit test to determine if your pump is providing the proper volume of water? Basically you’re looking for the pump to push 60 –100ml of water out of the group in 10 seconds. If you get less than this that is your problem..
Okay! Last theory then. There is a small hole in your heat exchanger and the venturi effect of the water flow is drawing a slight amount of very hot boiler water into the brew water stream. Far fetched, perhaps, but as Sherlock Holmes has said, "Once you eliminate the impossible, that which remains, no matter how improbable, is the solution.
If it isn't this, we have to assume that your machine is possessed by an evil spirit and you need to call a priest. If no priest is available then Jim Schulman or Dan Kehn should do.
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