GlennV Senior Member Joined: 27 Oct 2011 Posts: 29 Location: UK Expertise: I love coffee
Posted Sun Mar 11, 2012, 6:38am 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 ...
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.
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?
I could have ground even finer
I could have steeped even longer, although the brewer is so small it loses heat fast (even w/insulation)
I could have used a lower brew ratio
I could have aged the coffee a few more days (it's 6 days off of roast)
I could have stirred a little more while brewing
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!
Posted Mon Mar 12, 2012, 2:26am Subject: Re: coffee refractometer
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.
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.
TonyVan Senior Member Joined: 24 May 2010 Posts: 276 Location: Pacific Northwest Expertise: I love coffee
Espresso: GS/3, La Pavoni Grinder: Macap M7K, Rocky Drip: Kone
Posted Mon Mar 12, 2012, 4:47pm Subject: Re: coffee refractometer
...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.
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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