Author Topic: Measuring Brew Strength - Optical Refractometer - try it travel thread!  (Read 11628 times)

ecc

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This was tougher to write up than I imagined.  If you don't get it, it is likely because I am not explaining it well.  Please ask questions!



The overview (poor mans extract mojo):
Optical refractometers have been used for a while to provide a practical and quick method of determining relative sucrose content of produce.  Basically, if you can get enough light through a liquid, you can tell how dense it is by how much it bends light.  The refraction is indexed onto a scale, various refractometers have different scales and ranges.  Someone in a lab coat spends a huge amount of time correlating the refraction index to sucrose content, or tds in coffee, or you can just use it as a relative measure to compare between two samples.

Quick Directions for use:
 -- Let a coffee sample cool to room temperature
 -- use a pipette, a clean stirrer/straw and the finger over the top trick to get liquid up, or somehow drip enough liquid to cover the lower glass plate
 -- gently lower the plastic cover onto the glass plate, you may need to do this a few times to eliminate bubbles between the lower glass plate and the plastic cover
 -- point the business end towards a light source, look in the other end
 -- the brix scale is indicated by the amount of the scale covered in blue

TDS is 85% of Brix,  use this extraction chart as a guideline as to what the tds "should" be for your coffee:water ratio.  Note how the 19:1 ratio has the biggest window of "acceptable" tds values.  Please don't let this dogma blind you from the value of objective measure, comparison between brew methods, consistency, quickly adjusting grind for new brewing methods, etc.  I end up always skewed to the strong side, but then my water:coffee runs more like 16:1 .

Enough for now, lots to talk about! Sign up for a spot in the travel loop, ask a question, or hit the flameguns!


Travel loop:
B|Java
« Last Edit: February 26, 2011, 09:32:35 PM by ecc »

BoldJava

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #1 on: February 26, 2011, 10:04:16 AM »
Cool.  First port of call:  Lake Cheddar.

I have the TDS meter figured out so I will run with the wolves and compare the two.  Write up pending.

B|Java

Tex

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #2 on: February 26, 2011, 11:42:02 AM »
I've been intrigued by this and have wondered about the merit of its use for coffee. Would a refractometer show anything other than the percentage of solids in the coffee? How would this be useful when SO's have varying flavor characteristics that add to the coffee strength (mouth feel?)?

I'll be watching the results of everyone's use to see if I might want to use mine. BTW: A friend at A&M had a spare that I was be able to swap a Gaggia pump for years ago - now where did I put that bleepin' thing?

Offline John F

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #3 on: February 26, 2011, 12:13:46 PM »
Tex..

TDS meter gives you solids brix/refractometer is sugar.

As for your question of usefulness...depends on who you ask.
« Last Edit: February 26, 2011, 12:16:39 PM by John F »
"At no point should you be in condition white unless you are in your bed sleeping with your doors locked."

Lee Morrison

ecc

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #4 on: February 26, 2011, 12:16:24 PM »
Some interesting further reading, http://www.jimseven.com/2009/06/16/extractmojo/, and a corrected link to the brewing control chart mentioned in the middle of blog entry.

Here is a goldcup brochure as well.

Brix is just the calibration scale used to display the refractive index.  Most TDS meters measure ohms.
« Last Edit: February 26, 2011, 12:18:36 PM by ecc »

Tex

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #5 on: February 26, 2011, 12:19:36 PM »
Tex..

TDS meter gives you solids brix/refractometer is sugar.

As for your question of usefulness...depends on who you ask.


OK, then that begs the question: The same bean at different roasts will have varying amounts of dissolved sugars, so you'd use this tool to determine the roast level to aim for?

ecc

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #6 on: February 26, 2011, 12:32:43 PM »
Tex..

TDS meter gives you solids brix/refractometer is sugar.

As for your question of usefulness...depends on who you ask.


OK, then that begs the question: The same bean at different roasts will have varying amounts of dissolved sugars, so you'd use this tool to determine the roast level to aim for?

No, this is like expecting the electrical resistance to have the same correlation to tds in water vs. coffee.  Remember, we aren't measuring sucrose or dissolved solids directly, we are using a (hopefully) well established relationship between those properties and something way easier to measure.

Tex

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #7 on: February 26, 2011, 02:14:09 PM »
Tex..

TDS meter gives you solids brix/refractometer is sugar.

As for your question of usefulness...depends on who you ask.


OK, then that begs the question: The same bean at different roasts will have varying amounts of dissolved sugars, so you'd use this tool to determine the roast level to aim for?

No, this is like expecting the electrical resistance to have the same correlation to tds in water vs. coffee.  Remember, we aren't measuring sucrose or dissolved solids directly, we are using a (hopefully) well established relationship between those properties and something way easier to measure.

Good enuff reason NOT to go digging around in the garage.

Offline MGLloyd

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #8 on: February 26, 2011, 02:58:21 PM »
Speaking as a former analytical chemist, I am unsure how measuring the TDS correlates with the subjective sense of taste.  Your preferred coffee concentration may not be my preferred coffee concentration. 
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ecc

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #9 on: February 26, 2011, 03:23:19 PM »
Speaking as a former analytical chemist, I am unsure how measuring the TDS correlates with the subjective sense of taste.  Your preferred coffee concentration may not be my preferred coffee concentration. 

I totally agree.  I am skeptical as to the validity of an ideal and universal extraction rate, brewing concentration, roast profile, etc.  I also suspect that the research and data backing the gold cup standard might not be the most rigorous.  I don't think that precludes me from thinking the measurement is useful and/or interesting, and I do believe it has made my cup a little better.

This refractometer (0-10Br) is useful for brewed coffee only.  It can measure how consistent your brew strength is from day to day, from method to method, from person to person.  It can also provide a quick way to adjust grind/brew time for a new brewing method, or map/check approximate grind settings across grinders.




Offline John F

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #10 on: February 26, 2011, 03:26:34 PM »
Speaking as a former analytical chemist, I am unsure how measuring the TDS correlates with the subjective sense of taste.  Your preferred coffee concentration may not be my preferred coffee concentration. 

As a non chemist coffee fool I've been saying the same thing from the first time I ever heard about using TDS meters and refractometers with coffee.

Knowing how many PPM of random solids are in a cup does not tell me what they taste like. I see the usefulness for standardization but that is about all.
"At no point should you be in condition white unless you are in your bed sleeping with your doors locked."

Lee Morrison

Offline peter

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #11 on: February 26, 2011, 03:38:11 PM »
Speaking as a former analytical chemist, I am unsure how measuring the TDS correlates with the subjective sense of taste.  Your preferred coffee concentration may not be my preferred coffee concentration. 

As a non chemist coffee fool I've been saying the same thing from the first time I ever heard about using TDS meters and refractometers with coffee.

Knowing how many PPM of random solids are in a cup does not tell me what they taste like. I see the usefulness for standardization but that is about all.

But, if someone has the same coffee, ground at the same coarseness, and the same water, can't they bracket their brew ratios, checking the PPM/brix of each one until they find a ratio that tastes 'right' and then use that ratio going forward and check with the gadget in subsequent days to see if the ratio is holding true?

How's that for a run-on sentence, complete with commas and apostrophes?  Jeffo should comment now.   ;)
Quote of the Day; \"...yet you refuse to come to Me that you

ecc

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #12 on: February 26, 2011, 03:39:52 PM »
Speaking as a former analytical chemist, I am unsure how measuring the TDS correlates with the subjective sense of taste.  Your preferred coffee concentration may not be my preferred coffee concentration. 

As a non chemist coffee fool I've been saying the same thing from the first time I ever heard about using TDS meters and refractometers with coffee.

Knowing how many PPM of random solids are in a cup does not tell me what they taste like. I see the usefulness for standardization but that is about all.

Knowing the ratio of coffee to water does not tell you what it tastes like, nor does measuring the brew temperature, the brew time, or checking to see how hard/soft your water is.

Just another tool...

Offline John F

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #13 on: February 26, 2011, 04:16:27 PM »
But, if someone has the same coffee, ground at the same coarseness, and the same water, can't they bracket their brew ratios, checking the PPM/brix of each one until they find a ratio that tastes 'right' and then use that ratio going forward and check with the gadget in subsequent days to see if the ratio is holding true?


I can't figure out what you are asking and I'm still inclined to say no.

In fact I'm pretty sure it's no.  ;)

Rephrase please....
"At no point should you be in condition white unless you are in your bed sleeping with your doors locked."

Lee Morrison

crholliday

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Re: Measuring Brew Strength - Optical Refractometer - try it!
« Reply #14 on: February 26, 2011, 04:20:13 PM »
I'm pretty sure Peter is describing some baselining for 'standardization' of a single coffee.

I think John's answer will then be 'yes'.

:)