Filternatives

I admit, when I ordered his VST Refractometer, Vince from VST labs already suggested I might order extra syringe filters but at the time, 50 of those seemed a lot to get started. Of course I rushed through most of them in the first week so I ordered 50 more. They don't come cheap though: $89 for fifty plus $34 for shipping to NL.

As I ordered 500 pipettes and a box of #7syringes locally from Hinmeijer, I wondered if compatible filters could also be found nearby. René Hinmeijer is looking into this and Adriaan, a fellow roaster from the Dutch forum, quickly found a possible alternative from an Asian company reselling German filters: Minisart by Sartorius. These cost me not much more than the postage of the original VST filters. They are "high flow" syringes with 0.2 micrometer pores. I do not know the pore size of the originals though.

Since the special filters are not necessary when measuring coffee that has passed through paper filters, like drip coffee, I also got a Hario V60 Dripper.

If the measurements of the VST and the German filters come close, the latter would be a great alternative and if a particular measurement is most critical, I could double check the measurement with the original filter, to be sure my readings are compatible with what others would get with the same lab standard.

I took 20g of Finca Tamana beans roasted 17 february (Tonino # 84 today) and pulled 30g espresso. Cooled in a larger ceramic cup, stirred well, filled two identical syringes, screwed a VST on one, a Minisart on the other and pushed a few ml's with each into their own identical shot glass.

Even though the Minisart is a "high flow" filter, it took much longer (and more power) to push enough fluid out of it. Afterwards, on close up pictures of the filter, it showed two cracks. I can understand why the manual advises to "take care when using syringes with a volume less than 10ml since they can generate a pressure greater than the maximum operating pressure of the Minisart unit."

Next I took two brand new pipettes and did my measurements after first calibrating the refractometer and cleaning the eye of the meter with alcohol between measurements.

The Minisart sample showed 11.1 % TDS and the VST sample showed 11.2 % TDS.

So that's very very close and if subsequent comparisons turn out as good, this will be a fine alternative as long as I keep my glasses on and take care not to explode the filters.

The drip alternative (the leftover poured onto a filter which I made wet with tap water first) showed 9.8 % TDS on the first ml's that passed. I should try this again, this time on a dry filter paper and with more espresso, taking the time to let it all drip through.

Extraction ready to measure

VST filter and Minisart sister

Two samples from same extraction

Minisart after use, notice the hair cracks

Both syringes & filters after the job

Result of VST measurement visible

The drip test, not as close to the original: diluted & not fully filtered yet