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Measuring Brew Strength - Optical Refractometer - try it travel thread!
ecc:
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
BoldJava:
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:
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?
John F:
Tex..
TDS meter gives you solids brix/refractometer is sugar.
As for your question of usefulness...depends on who you ask.
ecc:
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.
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