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GlennV
Senior Member


Joined: 27 Oct 2011
Posts: 29
Location: UK
Expertise: I love coffee

Posted Sun Mar 11, 2012, 7:38am
Subject: Re: coffee refractometer
 

If I've interpreted it correctly (with the last column being the estimated amount of coffee solids left after you've taken out the samples) then the precision in your range test is quite remarkable - when I've used a standard digital refractometer I've see the equivalent of the 1st decimal place fluctuate. I'm almost sold on one of these Lab ones ...
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andys
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andys
Joined: 10 May 2003
Posts: 813
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Sun Mar 11, 2012, 11:23am
Subject: Re: coffee refractometer
 

Netphilosopher Said:

Initial brew and Deyhdration:

22g Coffee
232.1g brew water

199.6g Produced Coffee
1.95% TDS (VST measurement)

49.3g Wet Puck of Spent Grounds, Wet (into oven for dehydration)
185.5g Coffee Sample (into oven for dehydration)  (Coffee lost during sampling = 14.1g)

Stabilized dry masses:
4.2g Dried TDS
17.5 Dried grounds

(both measured at room temperature once dry and stabilized by leaving in oven for the day with the oven off)

Backcalculated strength from recovered TDS: 4.2/185.5 = 2.264%
TDS in "lost" sampled coffee = 2.264% * 14.1 = 0.319g

Complete TDS = 4.52g
total recovered = 17.5+4.52 = 22.02 (22g)

Posted March 10, 2012 link


Steve:

As I've previously said, I ran various evaporation experiments a while back and had great difficulty getting consistent results: collecting every bit of spent grounds, knowing what oven temps to use and when to stop drying, preventing rapid rehydration from the atmosphere, etc.

The example above is amazing: you go through all that, somehow lose 5.2g of mass to unknown places (22.0 + 232.1 does not equal 199.6 + 49.3), and still achieve perfect 22.0 gram solids recovery? Wow.

Based on the literature, the dry coffee probably had some moisture content, 1%-2%, which would mean a few tenths of a gram. Apparently you were able to dry the two fractions down to exactly the original moisture content?

I'm not disputing your results, I believe you got what you got; but there's no way I'm gonna try to duplicate it. After using the refractometer and learning some of the procedures for getting good data with it, I sure don't want to go back to dehydration!

I don't feel I have golden taste buds, but unlike you I usually find the VST refractometer-derived results correlate well with the generally accepted taste ranges. In other words, when my VST yields are around 17%-18% the flavors usually seem dry and/or tart. In the 18.5-19.5 range I like the balance. If I get up around 20% it sometimes seems a little overdone, but I do not find the overwhelming bitterness and creosote that you found. Granted, I am usually tasting espresso, not an Aeropress concentrate like you appear to be brewing. I don't see why that would make a difference, but I don't know the answer.

People I respect who probably DO have golden taste buds also seem to agree with their VST refract results: George Howell, Dave Walsh, Scott Rao, James Hoffmann, etc.

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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Netphilosopher
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Joined: 14 Jan 2011
Posts: 1,602
Location: USA
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Posted Sun Mar 11, 2012, 3:12pm
Subject: Re: coffee refractometer
 

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iHaveFeet
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Joined: 5 Oct 2008
Posts: 105
Location: Victoria, B.C.
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Espresso: Mypressi Twist
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Posted Sun Mar 11, 2012, 6:42pm
Subject: Re: coffee refractometer
 

Netphilosopher Said:

AndyS (or anyone else) - do you have any recipes for brewed coffee that will result in TRULY overextracted coffee.

Posted March 11, 2012 link

Why not boil some espresso grind on the stove for half an hour or so? If the VST doesn't measure THAT as being over extracted then you can be 100% certain something fishy is going on. :D

Been highly enjoying following this thread, even though most of the discussion is out of my league. :)

Brendan
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andys
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andys
Joined: 10 May 2003
Posts: 813
Location: NY
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Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
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Roaster: PIDed Popper
Posted Sun Mar 11, 2012, 7:34pm
Subject: Re: coffee refractometer
 

Netphilosopher Said:

AndyS (or anyone else) - do you have any recipes for brewed coffee that will result in TRULY overextracted coffee

Posted March 11, 2012 link

Hi Steve:

I'm not sure any "recipe" is a sure thing (for reasons discussed below), but I gave it a try tonight at your request:

  • Preheated, inverted Aeropress with custom 1" thick hideously ugly insulation
  • 12.1g dry coffee dose
  • ground on Baratza Virtuoso setting 13 (my usual setting is ~18)
  • 199.5g water just off boil
  • gently stirred for 5 sec once every minute
  • Reverted Aeropress and began gently pressing at 6:30 min
  • finished pressing at ~8:00 min
  • yielded 176.4g beverage
  • stirred beverage and removed ~4ml into clean dry syringe
  • mounted filter and pressed ~2ml into room temperature demitasse
  • cooled in covered demitasse for 1 min
  • used clean, dry pipette to transfer a few drops on prism
  • after about half a minute got stable readings of 1.44%-1.45%

This came out to a 21% extraction yield. Sorry, it is only mildly overextracted (to my taste), not "TRULY" overextracted. I tried Steve, I really did.

It is late here and I don't want to be up all night. But I took a tiny sip and it was quite strong and somewhat harsh with a mildly bitter tinge. 98% of cafes in the USA would be PROUD to serve it. (Although they'd be too cheap to use that much dry coffee.)

Why wasn't the yield higher?

  1. I could have ground even finer
  2. I could have steeped even longer, although the brewer is so small it loses heat fast (even w/insulation)
  3. I could have used a lower brew ratio
  4. I could have aged the coffee a few more days (it's 6 days off of roast)
  5. I could have stirred a little more while brewing
  6. I could have used a different coffee (this one seemed unusually light).

Of all these factors, I think the coffee itself is critically important for proper extraction. Many 3rd wave roasters are trying to preserve varietal flavors by living on the bleeding edge of light roasting. If they somehow fail to get enough heat to the interior of the bean at the right time, or they pull the batch too early, it just doesn't taste or extract properly. Using the refract regularly, you can see this, even with the same varietal by the same roasting company from batch to batch.

You don't say whose beans you're using, and you don't have to name names, but have you tried another roasting company? Try a moderately roasted or even dark roasted batch from someone else, let it rest for at least a week, and then see what kind of yield you get. When brewing, use a fairly low brew ratio, fine grind, plenty of steep time and agitate regularly. To be on the safe side, in case a lot of fines have come through your paper disc, use a syringe filter before measuring with refract!

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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andys
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andys
Joined: 10 May 2003
Posts: 813
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Mon Mar 12, 2012, 3:26am
Subject: Re: coffee refractometer
 

TonyVan Said:

It's always been my (possibly mistaken) impression that "fines-is-fines" and their mean and median size within the fines portion of the typical (bimodal) distribution curve was essentially unaffected by grinder's adjustments (within the espresso range).  

If so, then the "extra-fine fines" that might theoretically be generated by slightly tighter grinding (at least within your context here of moderately under-dosing a basket) probably don't really occur.  This appears to be borne out in your conclusion that you don't notice silty espresso.

Posted March 10, 2012 link

Good point, Tony. I'm not sure of the answer.

Even if the median size of the fines doesn't change, there might be a higher percentage of them due to tighter overall grinding. If that is the case, more particles on the small end of the fines distribution curve might be available to sneak through the filter.

The fact that I usually don't notice them could simply be my lack of awareness. To a certain extent, it could be a machine thing. Kees might say that my Speedster's progressive preinfusion setup cuts down on the number of fines that migrate to the bottom and therefore are in position to make it through the holes. Sometime I'll install a "progressive preinfusion defeater device" on the machine to enable easy A/B testing of this and other preinfusion-related effects.

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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Netphilosopher
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Joined: 14 Jan 2011
Posts: 1,602
Location: USA
Expertise: Just starting

Posted Mon Mar 12, 2012, 4:45am
Subject: Re: coffee refractometer
 

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mitch236
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Joined: 7 Nov 2003
Posts: 64
Location: Delray Beach
Expertise: I love coffee

Espresso: Linea Single Group (PID,...
Grinder: Mazzer Robur E
Posted Mon Mar 12, 2012, 6:24am
Subject: Re: coffee refractometer
 

tek Said:

That is great feedback. Which version do you guys have, Lab or Standard?

Posted March 9, 2012 link

I bought the lab version also.  I'm sure the regular version would be good enough though.  I'm just an over the top kind of guy.  Anyone remember Home Improvement?
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TonyVan
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Joined: 24 May 2010
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Expertise: I love coffee

Espresso: GS/3, La Pavoni
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Posted Mon Mar 12, 2012, 5:47pm
Subject: Re: coffee refractometer
 

andys Said:

...To a certain extent, it could be a machine thing. Kees might say that my Speedster's progressive preinfusion setup cuts down on the number of fines that migrate to the bottom and therefore are in position to make it through the holes. Sometime I'll install a "progressive preinfusion defeater device" on the machine to enable easy A/B testing of this and other preinfusion-related effects.

Posted March 12, 2012 link

Thanks - that may be a chunk of the answer. I've had a (manifestly unproven) suspicion that sophisticated pre-infusion or ramp-to-pressure schemas from makers such as KVDW or LM may account for some of the quality and especially the oft-mentioned "forgiving nature" of these particular machines.   Andy, when you DO develop a PPDD (hey - will there be a special package deal when purchased with a Schnozzola?) it'll be interesting to see what you can tease out.

Sorry to all for any interruption - this was a little tangential to the central discussion of this thread, which is very interesting and getting somewhere, so thanks and now back to our regularly scheduled programming.
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andys
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andys
Joined: 10 May 2003
Posts: 813
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Mon Mar 12, 2012, 6:06pm
Subject: Re: coffee refractometer
 

Netphilosopher Said:

I'm asking for a recipe we (this to anyone else with a VSTcr) can replicate, with a coffee we can replicate.

Posted March 12, 2012 link

Everyone's grinder is different, everyone's water is different, we stir differently, and the batch to batch Eight O Clock coffee is probably a little different in Michigan than it is in NY.

Even when we try our best to follow a standard recipe, the results inevitably vary.

The kind of "recipe" that I'd favor would be something like this:

"Aeropress, 12g dry coffee, 200g water @200F, 4 min steep time, grinder set at whatever it takes to achieve a 19.5% extraction yield."

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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