So I tested my pour-over coffee with cheap a Brix refractometer... - Page 5

Coffee preparation techniques besides espresso like pourover.
Pressino

#41: Post by Pressino »

By potentially more accurate I should have instead said potentially more precise, since with the 0 to 10 scale it will be easier for an observer to repeatedly read the refractometer index when coffee with the same TDS are tested. Not quite as good as having some sort of vernier scale but with a similar benefit to make readings more precise. By resolution I was referring to the number of digits displayed on the digital meter.

I understand exactly what the author reported in the article I cited. I know the limits of handheld optical refractometers versus more accurate and precise lab instruments, since I began using them in college and afterward in my work.

I really don't have anything more to add to my previous comments and I'm certainly not looking to argue with those (and perhaps you are one) who have invested a lot of money in things like the VST refractometer and believe the money has been well spent. More power to those folk. If someone gave me one for free or they were under $100, I would probably get one. It would certainly be easier to use than the optical device. I really do know how to use my optical one to get the most accurate and repeatable measurements of which the instrument is capable, and that works just fine for me. 8)

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Brewzologist
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#42: Post by Brewzologist »

jpender wrote: I guess it depends on what you are happy with. If you have a device that has an uncertainty of ±0.1% TDS, for brewed coffee that will translate into an extraction yield uncertainty of about 1%. So suppose you make coffee, measure it and get an EY of 20%. Then you make another cup and get an EY of 21%. You won't know if the second cup was more extracted or if it's just measurement noise.
FWIW: what I'm happy with is using an optical refractometer more as a trending device. When dialing in a new recipe I ultimately go by taste, but since my taste is subjective I can (and do) fool myself into thinking I've gone too far one way or the other at times. Say I'm trying a new pour-over method, or coffee/water ratio for a bean and I think I'm tasting under/over extracted notes. So I pull out my my optical refractometer to see where my trend is heading from sample to sample; say 20, 23, 26% EY. I know that any one of those numbers cannot be relied upon to be accurate. But the trend, coupled with my taste experience, provides some level of correlation to help me offset any sensory bias as I dial-in a recipe.

Is this a reasonable use of an optical refractometer, or am I all wrong here?

jpender

#43: Post by jpender »

Brewzologist wrote:...So I pull out my my optical refractometer to see where my trend is heading from sample to sample; say 20, 23, 26% EY. I know that any one of those numbers cannot be relied upon to be accurate. But the trend, coupled with my taste experience, provides some level of correlation to help me offset any sensory bias as I dial-in a recipe.

Is this a reasonable use of an optical refractometer, or am I all wrong here?
If that resolution still helps you dial in then it's totally reasonable.

I also have an inexpensive refractometer, one with a 0-18% Brix range. My thought was to use it for espresso where less precision is needed. I did an initial test where I pulled three shots. For each shot I prepared filtered samples for both the refractometer and my kitchen oven. In the past I've mailed samples to people with VST refractometers who were willing to test them. My oven dehydration results matched the VST results to within 0.02% TDS. So it's a reasonably accurate, albeit time consuming, method.

When I compared the optical refractometer readings to my oven results the refractometer readings differed by +0.05%, -0.01%, -0.16% TDS. That was actually kind of encouraging. But when I tested the same three samples the next day with just the refractometer they had all shifted by 0.1 Brix. So something I was doing, maybe related to the temperature, was resulting in inconsistency.

I've been meaning to do some more tests but with the pandemic my wife is working at home and she hates coffee. The smell of coffee samples drying in the oven is definitely not her favorite thing!