WonderClown Senior Member Joined: 17 Apr 2007 Posts: 217 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Sat May 2, 2009, 9:38am Subject: TDS: PPM vs. percent
So I just got an HM Digital TDS meter (TDS-3) for other purposes, and decided to test my coffee strength. I'm reading around 1210ppm. The SCAA Golden Cup standard, I understand, is 1.25%. That's suspiciously close, except for an order of magnitude -- 1.25% should be 12500ppm (=12.5ppt=1.25pph). My coffee is not an order of magnitude weaker than it should be. Am I wrong that 1% = 1pph = 10ppt = 10,000ppm?
Of course, if I'm right, and I should be reading roughly 12,500ppm for a "gold cup", then that is over the range of my meter. I would expect it to just read its max, or flash an error code, rather than giving me roughly the reading I expect, except an order of magnitude off. I found a thread over on coffeed.com where somebody is getting similar readings:
Anybody care to make some guesses or offer enlightenment?
EDIT: I answered my own question by preparing some salt solutions of different concentrations. When used with something over its maximum range, instead of reading the max or flashing an error code, it gives a low reading. It's almost like it "wraps around", which doesn't make much sense for something like this. Anyway, there you have it, for future reference -- don't use HM Digital TDS meters for measuring coffee directly. You have to dilute it first to get it into the TDS range of the meter. (Make sure to dilute with distilled water.) I haven't tried this yet, but I assume it will work.
Posted Sat May 2, 2009, 10:51am Subject: Re: TDS: PPM vs. percent
WonderClown Said:
So I just got an HM Digital TDS meter (TDS-3) for other purposes, and decided to test my coffee strength. I'm reading around 1210ppm. The SCAA Golden Cup standard, I understand, is 1.25%. That's suspiciously close, except for an order of magnitude -- 1.25% should be 12500ppm (=12.5ppt=1.25pph). My coffee is not an order of magnitude weaker than it should be. Am I wrong that 1% = 1pph = 10ppt = 10,000ppm?
Of course, if I'm right, and I should be reading roughly 12,500ppm for a "gold cup", then that is over the range of my meter. I would expect it to just read its max, or flash an error code, rather than giving me roughly the reading I expect, except an order of magnitude off.
You are correct, of course: 1.25% = 12,500 ppm. The SCAA Golden Cup program had been incorrectly saying 1.25% = 1,250 ppm for years until they quietly changed their charts in Atlanta this year.
If you're truly interested in measuring your coffee strength, get a refractometer from George Howell Coffee Company. It will be far more accurate than the conductivity meter.
WonderClown Senior Member Joined: 17 Apr 2007 Posts: 217 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Sat May 2, 2009, 10:59am Subject: Re: TDS: PPM vs. percent
andys Said:
If you're truly interested in measuring your coffee strength, get a refractometer from George Howell Coffee Company. It will be far more accurate than the conductivity meter.
I'd be happy to get within +/-10%. It's definitely not worth $300+ to me for this purpose. I didn't even buy this meter specifically for coffee, but rather for checking reverse osmosis membrane performance -- I just figured that now that I have a TDS meter, I might as well test my brew strength. (And the RO filter is not specifically for coffee -- I know that RO tends to produce water softer than you want for coffee.)
Luca Moderator Joined: 27 Jan 2004 Posts: 2,658 Location: Melbourne, Australia
Espresso: H: Maver W: FB-80 Grinder: H: Super Jolly W: Brasilia... Vac Pot: Hario TCA-2 Roaster: Sample Roaster at Work
Posted Sun May 3, 2009, 2:46am Subject: Re: TDS: PPM vs. percent
andys Said:
You are correct, of course: 1.25% = 12,500 ppm. The SCAA Golden Cup program had been incorrectly saying 1.25% = 1,250 ppm for years until they quietly changed their charts in Atlanta this year.
Interesting that you should say this. I asked this question during the golden cup certification program and the instructors didn't really seem to know the answer.
I'm told that new SCAA Executive Director Ric Reinhart has been aggressive at trying to reform the screwed up Golden Cup program. But change doesn't come easily, even when it's obvious the old program was flawed.
I wasn't at the show, so I'm just getting this info second hand.
I believe the SCAA instructors abandoned the approach of subtracting the ppm of the brew water from the measured ppm of the finished coffee. Although this method is technically correct, the fact that coffees are now correctly measured at ten times what they used to be makes it nearly irrelevant (ie, the old mistaken way: 1300ppm coffee - 200ppm water = 1100ppm extraction; the new correct way: 13,000ppm coffee - 200ppm water = 12,800ppm extraction).
Supposedly the SCAA bought multiple units of Terroir's new software and refractometer, but the Golden Cup instructors stuck to their old inaccurate TDS conductivity meters and continued to use paper charts.
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