Zentrifugalbeschleunigung
I'm so happy with this machine, in part because I learn beautiful new words from the manual, like Zentrifugalbeschleunigung. Abbreviated RZB for relative Zentrifugalbesleunigung. It's the German word for the g-force endured by the sample that's spinning around the centrifuge axis.
The synonym is just as beautiful: Schleuderziffer. With technical manuals like this, who needs poetry?
This value is more meaningful than just the RPM (rotations per minute) because a compact sample spinning closer to the axis experiences less centrifugal force than a sample that's hanging further away from the center of the rotor.
The machine has a display / keypad combination to enter these values and then it calculates and displays the realtime Zentrifugalbescheunigung during the procedure.
The previous owner never used the programmable options (he just inserted a sample, set the speed, pressed start and after a given time pressed stop) so I found it especially thrilling to have the machine activate this part of its capabilities for the first time.
I also measured the exact distance of the top of the fluid to the axis/center of the rotor and to the bottom tip of the fluid in the glass tube. If this value is fed into the machine it not only displays the rotations-per-minute but also the relative centrifugal force on the sample.
In the current program, the machine takes 60 seconds to slowly build up a speed of 3500 RPM, maintaining this speed for 7 minutes before braking at a very moderate force aiming to come to a full stop in 120 seconds, and below 500 RPM there is no braking force anymore, just free running slowing down to a full stop.
I measured the ambient temp, took 20g beans for the VST 20g basket (grinds measuring #99 on the Tonino scale), extracted 30.3g using the Londinium (releasing steam just before locking in the PF to activate the heating element to build up maximum pressure in the boiler / pre-infusion, lowering the lever again as the first drops fell from the naked PF, so a sort of "Fellini move" to get extra pressure on the first moments of extraction), stirred the extraction vigorously with the syringe, taking a 7g sample for the centrifuge, a 5g sample for the VST filter and drinking the rest.
Before this, I weighed the glass tubes until I matched two that are 15g each. I filled one with 7g water, the other with the 7g espresso and ran program #1 specified above.
Meanwhile I calibrated the VST refractometer with distilled water from the old precision lab fluid dispenser in the picture (a very nice contraption of fragile glass tubes into valves and a volumetric regulator).
Then I stirred, VST-filtered and measured three times the sample I saved: 10.9, 11 and 11, so noted 11% TDS
Next I took samples (with different new pipettes) from the very top of the centrifuged sample, from the middle and from close to the bottom: 11.1% -- 11.2% -- 11.1% so it seems it doesn't matter much how high or deep I go to get my sample with the pipette.
Noting the VST filter sample as 11% TDS and the centrifuged sample as 11.1% I would get 17.3% or 17.4% extraction (rounding off to one decimal).
Again, the centrifuge seems a fine alternative to filtration.
Below is a picture I made yesterday of the sediment in the glass tube. I would like to weigh it but it's probably so very light, the few remaining drops of fluid in the tube will probably weigh more so it would be hard to estimate the weight of the sediment.
The synonym is just as beautiful: Schleuderziffer. With technical manuals like this, who needs poetry?
This value is more meaningful than just the RPM (rotations per minute) because a compact sample spinning closer to the axis experiences less centrifugal force than a sample that's hanging further away from the center of the rotor.
The machine has a display / keypad combination to enter these values and then it calculates and displays the realtime Zentrifugalbescheunigung during the procedure.
The previous owner never used the programmable options (he just inserted a sample, set the speed, pressed start and after a given time pressed stop) so I found it especially thrilling to have the machine activate this part of its capabilities for the first time.
I also measured the exact distance of the top of the fluid to the axis/center of the rotor and to the bottom tip of the fluid in the glass tube. If this value is fed into the machine it not only displays the rotations-per-minute but also the relative centrifugal force on the sample.
In the current program, the machine takes 60 seconds to slowly build up a speed of 3500 RPM, maintaining this speed for 7 minutes before braking at a very moderate force aiming to come to a full stop in 120 seconds, and below 500 RPM there is no braking force anymore, just free running slowing down to a full stop.
I measured the ambient temp, took 20g beans for the VST 20g basket (grinds measuring #99 on the Tonino scale), extracted 30.3g using the Londinium (releasing steam just before locking in the PF to activate the heating element to build up maximum pressure in the boiler / pre-infusion, lowering the lever again as the first drops fell from the naked PF, so a sort of "Fellini move" to get extra pressure on the first moments of extraction), stirred the extraction vigorously with the syringe, taking a 7g sample for the centrifuge, a 5g sample for the VST filter and drinking the rest.
Before this, I weighed the glass tubes until I matched two that are 15g each. I filled one with 7g water, the other with the 7g espresso and ran program #1 specified above.
 |
| Ready to measure |
Meanwhile I calibrated the VST refractometer with distilled water from the old precision lab fluid dispenser in the picture (a very nice contraption of fragile glass tubes into valves and a volumetric regulator).
Then I stirred, VST-filtered and measured three times the sample I saved: 10.9, 11 and 11, so noted 11% TDS
Next I took samples (with different new pipettes) from the very top of the centrifuged sample, from the middle and from close to the bottom: 11.1% -- 11.2% -- 11.1% so it seems it doesn't matter much how high or deep I go to get my sample with the pipette.
Noting the VST filter sample as 11% TDS and the centrifuged sample as 11.1% I would get 17.3% or 17.4% extraction (rounding off to one decimal).
Again, the centrifuge seems a fine alternative to filtration.
 |
| Measurements ready |
Below is a picture I made yesterday of the sediment in the glass tube. I would like to weigh it but it's probably so very light, the few remaining drops of fluid in the tube will probably weigh more so it would be hard to estimate the weight of the sediment.
Weighing the residu can be quite a task, Wybo writes me in Dutch. It involves washing a few times with a few ml's of distilled water (along the inside wall of the tube), centrifuge this off a few times, decant, then dry in a desiccator, weigh, clean tube and weigh again, using a precision balance to 0,1 of a milligram...
"Gewichtsbepaling van het residu is inderdaad lastig. Je zou het eerst
twee of drie keer moeten behandelen door:
1. spoelen met een paar milliliter gedestilleerd water (langs de
buiswand rondom naar beneden spoelen,
2. Afcentrifugeren
3. Decanteren
En tenslotte drogen in een exsiccator, wegen, buis schoonmaken en
opnieuw wegen. Je houd maar een paar milligram over, waarvoor je dus een
balans nodig hebt die tot tiende milligrammen of minder gaat."
Reacties
Maar dan heb je ook nog een balans nodig die tot tiende milligrammen gaat.