Comparing filters, centrifuge and no filter

Someone asked me what's the difference between filtered and unfiltered espresso on the refractometer and I had to admit I hadn't thought "out of the cup" yet and never tried.

Now I did: I took 18g of a dark (Tonino #63) blend in the Reneka basket, ground it a bit too fine I guess and had a very slow extraction which I helped a bit by pushing up the lever on my Londinium. 29g espresso out.

Calibrated the VST refractometer at 19.9°C ambient and temp climbed to 20°C in the process so no need to recalibrate before I finished.

I poured the espresso into a large heavy cup and swirled to get it to cool down relatively quickly, then took measurements, after that put 7g in the centrifuge and repeated the measurements, adding the centrifuged one.

Before using the filters, I sucked up and pushed out the espresso with the syringe to get an optimal mix and I pressed out the drops straight onto the VST prism. Pressed GO three times on all samples.

SA=Sartorius filter

Shortly after half-cooling down:

VST filter: 9.5%
NO filter:  9.6%, 9.7%, 9.8% then staying 9.8%
SA filter:   9.6%

Then I did the centrifuge and after 10 minutes when the centrifuge was ready, using fresh filters on the more completely cooled sample, stirred well again:

VST filter: 9.8%
NO filter:  9.9%
SA filter:   9.8%
Centrifuged sample: 9.8%

I would need to do this more often, and preferably hear from others who are able to repeat this, but to me it indicates that a filter is useful, the VST filter assures you you are measuing the same way as the next guy, the cheapo filter I found is okay, but even NO filter works with just a small error if you stir very well and use a thoroughly cooled sample (and clean the refractometer well).


Devin Lee zei…
Can different cetrifuge rpm cause another result? e.g 7000 rpm 10000 rpm or pretty slow speed like 1000 rpm. I consider more cheeper auto centrifuge, or low price hand centrifuge.
Frans zei…
Deze reactie is verwijderd door de auteur.
Frans zei…
Thanks for your suggestion!

I compared the high speed program to a new program I entered:

30 seconds to 1000 rpm
4 minutes of 1000 rpm
1 minute to full stop

and the refractometer measured the exact same value on both samples.

So you don't need a super duper centrifuge!
Devin Lee zei…
Thank you! Have you ever try to measurement with extreme long preinfusion shot? In HB forum, there are no different yield between huge pre-infusion shot(W/ 3~4 notch finer grind) and standard shot(w/normal grind). I have great appreciation to your efforta and experiment. Thank you again.
Frans zei…
Hi Devin,

You're welcome! Yesterday I managed to get the extraction from 19 to 19.5% but the extreme pre-infusion and slow extraction time made the shot last 2 minutes and I did not like the taste. This morning too, when I tried both the HG One and the Mazzer at very fine grind, I did not get near 20% but I did dislike the dark oily extraction. 16-17 % seems more to my taste. I should try my Vario Home grinder, and also I must still repeat the extraction on the Rocket E61, might be very different.
Devin Lee zei…
If excepting taste favor is possible, very finer grind with extreme pre infusion could make more higher extraction? Does it make a sense? I made couple of shots from k10f with much finer grind with long p/i, and got favorable flavor. I used Light roasted bean for filter brew. If finer grind w/ long PI doesn't make highr extraction, I'll wonder about the cause.
Frans zei…
Age / freshness of beans could be a factor. On 5 weeks old beans that I roasted myself, I had a relatively fast flow AND 20.5 -- 21.5 % extraction over two shots just now. The taste was not spectacular.