I just realized an error in the way I thought things were plumbed which invalidates my hypothesis. I was going under the belief that the pump isolates the brew boiler from the grouphead, which I quickly found out was wrong when I looked up the Brewtus schematic.
So now there is no mystery either with the test results, as the presumed low pressure conditions inside the brew path never gets created for any significant amount of time as soon as the 3-way switch is activated. Looks like the only way now to further investigate my original issue, sourness in the cup, is via a pressurized measurement of the brew path via a Scace device or Eric's E61 grouphead thermocouple. On Feb 6, 4:43 am, cgfan <[email protected]> wrote: > I just ran a series of tests taking the temperature of the brew water > at the point where it passes the 5mm E61 grouphead bolt. Note that > these measurements were taken with a blind portafilter and the 5mm > grouphead bolt removed where a 0.2 degree accurate temperature probe > was loosely inserted. In this way the measurements were essentially > taken at atmospheric pressure, and not at the typical brewing > pressures during an extraction. > > This is justified per the reasoning in my last, last post above. That > is the initial brew-water which leaves the pump at the very start of a > shot, which is the water that will largely contribute to the > extraction of small volume shots such as the ristretto, will > essentially be nearly at atmospheric pressure as the air in the brew > path has not yet been displaced. In fact any shot whose volume is > smaller than, or close to that of, the volume of the entire brew path > may be subject to this effect. > > It is suspected that for all operating points whose combined desired > brew temp and temperature offset exceeds 100 deg C, then the brew > water will instantly cool to 100 deg C (and give up some steam in the > process), resulting in a cooler shot than expected. Note that this is > the case even if this brew water were to subsequently repressurize due > to the presence of tamped coffee in the p/f. The initial "fill" of > water in the brew path is not likely to regain much, if any, of this > lost temperature. > > So to test this hypothesis I ran a series of tests with the target > temp set to 96 deg C, but with an offset that was varied from -1 to -9 > deg C. As expected the data shows that there was no change to actual > depressurized water temps until the combined desired brew temp and > temperature offset dropped below 100 deg C. > > Note that before running each test I waited until the brew boiler > light switch ON, then swtiched to OFF. This insures that the brew > boiler temperatures were at their maximum possible temperature (an > entire hysteresis step, in my case 1 deg C, above the target boiler > temperature). > > Expected Estimated > Boiler Temp at Temp at > Setpoint Offset Temp G/H bolt P/F > > 96.00 -9.00 105.00 99.00 96.78 > 96.00 -8.00 104.00 99.00 96.78 > 96.00 -7.00 103.00 99.00 96.78 > 96.00 -6.00 102.00 99.00 96.78 > 96.00 -5.00 101.00 99.00 96.78 > 96.00 -4.00 100.00 99.00 96.78 > 96.00 -3.00 99.00 97.39 95.17 > 96.00 -2.00 98.00 96.78 94.56 > 96.00 -1.00 97.00 94.17 91.94 > > Note that the temperature measured at the G/H (where the 5mm allen > bolt normally resides) does not change until the boiler temperature > drops to 100 deg C or below. > > This perhaps explains my inability to eliminate sourness in the cup by > increasing either the set point or the offset temps, as my typical > setting of 96 with an offset of -8 already placed the brew water > boiler to exceed 100 deg C. > > This left me with no more "room" to affect an increase in brew water > temps for such a short shot. I would have to expel more than a brew > path's volume of water before I'd get the benefit of any 100+ deg C > brew boiler water. > > Note, however, that this hypothesis predicts that even a flush will > not take care of this effect, as a flush occurs practically at > atmospheric pressure. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Brewtus" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/brewtus?hl=en -~----------~----~----~----~------~----~------~--~---
