Socratic Coffee is doing another massive test as we speak with 3 different refractometers, dehydration and calibrated samples etc. I'm looking forward to them putting this to bed once and for all...

jpender wrote: For example, the unfiltered sample 1 measured about 0.3% TDS lower than sample 4. But when filtered, sample 1 measured 1.3% higher than sample 4.

You cannot compare values from the from filtered and unfiltered tables because they are not the same sample. Take a look at sample 1 from Atago filtered and unfiltered. One has a shot dose of 40.4 and another one has a shot dose of 40.

bachampion wrote:Socratic Coffee is doing another massive test as we speak with 3 different refractometers, dehydration and calibrated samples etc. I'm looking forward to them putting this to bed once and for all...

Hmm, not that many details and that was 20 days ago. Do you have more information?

No results yet but they have updates (last one was 6 days ago).

So far they have put in 20-30 hours into this experiment.

The VST filters are quite high quality and contain a prefilter to stop them from clogging, which allows them to be used multiple times bringing costs down. However I'm not sure how many uses you can on a single filter. 2? 3? more?

You can get a similar filter to the VST branded one (which contain a pre-filter) for slightly less money if you hunt:
https://scientificfilters.com/store/gla ... rs-cf59258
Note: Just make sure to purge a few ml each time to make sure you're getting a fresh sample when reusing filters.

I use 0.45um Nylon filters without a prefilter. They do clog quite quickly, so they're single use only. Iirc I paid about $65-70 off Amazon for 100 of these. Although subsequently I found the same ones on ebay (different brand name, same supplier product) for about $40 usd. You'll want to get Nylon instead of PTFE for coffee, and 0.45um size.


In terms of the question: are filters required? There was a older thread where Vince from VST talks about the requirement for filtration. IIRC Vince said in their testing that results can vary without using a filter. Sometimes results are okay and spot on, other times they're not. I wish I could remember the factors he described which influenced results. I'll try and dig up the thread (it's quite old now 6-10years?).

Follow up to last post. I found this classic thread comparing paper filter methods for brew coffee:
https://www.coffeegeek.com/forums/coffe ... 84&Page=12

There's quite a bit of interesting info in the thread. Such as how/why the TDS can climb if you re-sample the same coffee several days later.

I'll keep looking and see if I can find the espresso one talking about filter requirements.

felyko wrote:You cannot compare values from the from filtered and unfiltered tables because they are not the same sample. Take a look at sample 1 from Atago filtered and unfiltered. One has a shot dose of 40.4 and another one has a shot dose of 40.

Thanks for correcting me. I should have read the paper more carefully.

nickw wrote:Follow up to last post. I found this classic thread comparing paper filter methods for brew coffee:
https://www.coffeegeek.com/forums/coffe ... 84&Page=12

There's quite a bit of interesting info in the thread. Such as how/why the TDS can climb if you re-sample the same coffee several days later.

I'll keep looking and see if I can find the espresso one talking about filter requirements.

Very interesting. Thanks for sharing.

felyko wrote:You cannot compare values from the from filtered and unfiltered tables because they are not the same sample. Take a look at sample 1 from Atago filtered and unfiltered. One has a shot dose of 40.4 and another one has a shot dose of 40.

I misunderstood their second hypothesis:

Socratic Coffee wrote:2) samples using the VST syringe filters would have significantly different TDS readings compared to the TDS readings of samples without the VST syringe filters

It could be construed to mean two different things.

I got a used lab centrifuge because I have no desire to pay >$1 a filter.



Produces a result free of undissolved solids with no recurring costs after the initial investment of ~$200 (there are some cheaper models on ebay as well, I found several not quite as nice model <$100 "buy-it-now" options after placing my $200 bid cap on this one). Even buying in packs of 500 ($795 for 500 filters, $1.59 each and over $500 more than my centrifuge already) and 2 uses per filter ($.80/use), it takes less than 300 shots to pay off. With me pulling 2-5 a day and measuring each shot, it's a no-brainer.

Here's some more info on the subject for the interested: http://kostverlorenvaart.blogspot.com/2 ... ifuge.html