Uses and Abuses of Refractometers

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AssafL
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#1: Post by AssafL »

So many years have passed since my first post on H-B. It was La Macchina Fluffinata, my first attempt to reconcile distribution and normalization problems a new grinder I purchased (Mazzer Mini E) had developed. Luckily refractometry, well known in other aspects of cooking kicked in and showed us we could measure where the Mini E failed. Lately I have had a flurry of discussions about refractometers with several "scientists" over PMs and decided that it would make an interesting 1000 post to summarize what we discussed.

Refractometers are a useful device in the coffee lab. In combination with a 0.1g scale, it can provide objectivity in an otherwise very subjective effort to "improve" our coffee. I use double-quotes on the word "improve" since even deciding if some change results in an improved coffee is subjective.

But one gets the sense that refractometer readings are often misinterpreted - causing grinders like the EK43 to receive much attention (and dumping the Titans as a byline). I do think good baristas realize this (if not aware of why the refractometer math fails) - so (as one glaring example) I remember the EK43 sitting in the back of Sightglass Coffee while they were adamant that the Robur is as good as if not better. This was while some were continuing "the EY is important" path.

What can a refractometer do -
  • 1. Gauge the economic yield of a grinder. Economic yield is the amount of raw material needed for a unit of beverage or a gram of instant coffee. A higher EY achieved with a grinder or a roast profile means you'll need less raw coffee for an identical output. Example: Identical shots between a Robur and an EK43 will cost about 30% more on a Robur. For Nestle, higher EY always means less waste and a higher bottom line. For us hobbyists - it is up to the individual hobbyist to decide if economic yield is important. Robur's are still titans and many great coffee shops still prefer them. The cost is that you must updose the Robur.

    2. Associate EY statistics with grinder quality. EY statistics can and should be used to determine the quality of a grinder. An especially important optic into grinder performance is the need to WDT. If the output of a grinder improves by more than 1% after WDT - the normalization of the grinds is severely wanting. Examples: According to several tests Robur's (others) and Unaligned VL (mine) result in wider EY spreads (same coffee, same formula) than a Mythos, aligned VL and a Monolith. Inconsistent results means the Robur is less able to control the density in the puck.

    3. QA detect changes in process: If there is a change in EY that is outside the normal EY spread - it necessarily means something changed. Example: It could be as mundane as different coffee or coffee staling (time to reevaluate formula) - or it could be a major issue like a new batch of roasted coffee is underdeveloped or that whoever replaced the burrs caused alignment issues.

    4. Training tool for process & standard language . The proper utilization and interpretation of a refractometer reading requires the user to understand brewing mechanics and forces a common language. Example: Yield, Dose, Extraction Yield, etc. are all terms that became much more consistent after the introduction of the refractometer. However, under & over extraction (as related to flavor) are as obtuse as they were 10 years ago.

    5. Meteorologist: Sudden changes in EY due to clumps, static, etc. Example: Many a recent complaints on H-B regarding static happen during a dry spell in the complainer's city, state or country. What worked yesterday suddenly fails. Did the grinder break? Not necessarily. Before you buy a new grinder check weather.com and RDT.
What a refractometer cannot do -
  • 1. Correlate EY to flavor. Brew Control Charts can only work for a specific grinder, specific grind setting and a specific coffee (that together define the solubility of the puck). Switching grinders, grinder setting or coffee will lead to a different EY result since more (or less) of the puck will participate in making the cup. This does not affect the economic yield (Nestle will have to still buy more coffee for a low EY grinder) BUT it has major implication for the flavor (is the part that participates over or under extracted). Example: This is the mechanism that allows an identical calculation (say 21%) to be at once under-extracted and sour (e.g. for an EK43) and over-extracted and bitter, watery and astringent (for a Robur). This is also the same mechanism that explains why Robur 3-gen shots require so much updosing. Since a smaller portion of the puck participates in the brew.

    2. Tell you if you over or under extract*. One has to rely on flavor for this. * One caveat - if you dialed your grinder using flavor and measured it - comparing the next shot is valid as long as timing and parameters are held constant (this is the QA scenario). Of course if the next shot has severe channeling - the reading, obviously, will be misleading. It will be a low economic yield shot, but severely over-extracted flavors from the puck area where water got through.

    3. Equate higher EY with a better grinder. Higher EY does not necessarily mean a better grinder. All EY values means is does require larger doses for achieving an equivalent EBF with higher EY grinders.
    Example: Robur's are still titans and many great coffee shops still prefer them. The cost is that you must updose the Robur.

Example Use cases:
  • 1. Identifying an underdeveloped roast - identical grinder. Preferably identical coffee (two roasts). If one has a consistently higher EY - it is a more developed roast. Note - I do not know what happens farther into second crack. It may well be a maxima somewhere near FC+.

    2. Identify Grinder Faults - My current model for a grinder is: comminution -> filter -> normalizing -> distribution.
    a. Identifying misaligned burrs - two identical grinders w/same burrs - one has a higher EY after WDT - it is probably better aligned.
    b. Normalizing issues - if WDT increases EY consistently - the normalizer should be examined (paddles added, etc.).
    c. Filtering - Lower EY - More boulders get through (lower effective dose).

    3. Consistency checking (QC) - if EY is inconsistent - then you have a process or grinder problem.
Unclear Use Cases:
  • 1. Dulling burrs - in theory dull burrs create more fines. More fines should extract higher - but to achieve flow grinder gap is widened - so EY will go down. But not as a direct result of the burr.
Supportive Software:
  • 1. VST Coffeetools is a great calculator but unfortunately, makes an explicit connection between EY and flavor by introducing their "interactive" Brew Control Charts (while failing to canonize EY for the coffee and grinder at hand). It is misleading at best. It is recommended but with severe caution as to interpreting the readings.

    2. Atago Coffee PAL just shows you EY and lets you decide what to do with it. It is mundane - but it is not misleading.
Comments welcome (please feel free to shoot down errors and omissions).
Scraping away (slowly) at the tyranny of biases and dogma.

RyanJE
Posts: 1519
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#2: Post by RyanJE »

Interesting post! So one part I personally dont understand....
AssafL wrote:2. Associate EY statistics with grinder quality. EY statistics can and should be used to determine the quality of a grinder. An especially important optic into grinder performance is the need to WDT. If the output of a grinder improves by more than 1% after WDT - the normalization of the grinds is severely wanting. Examples: According to several tests Robur's (others) and Unaligned VL (mine) result in wider EY spreads (same coffee, same formula) than a Mythos, aligned VL and a Monolith. Inconsistent results mean the Robur is less able to control the density in the puck.
I think its fairly common practice for people to WDT the monoliths. Does this imply quality issues with them because of the need to WDT? I am not sure I see the correlation of what you are proposing.
I drink two shots before I drink two shots, then I drink two more....

nuketopia
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Joined: 8 years ago

#3: Post by nuketopia »

AssafL wrote: 1. VST Coffeetools is a great calculator but unfortunately, makes an explicit connection between EY and flavor by introducing their "interactive" Brew Control Charts (while failing to canonize EY for the coffee and grinder at hand). It is misleading at best. It is recommended but with severe caution as to interpreting the readings.

Comments welcome (please feel free to shoot down errors and omissions).
I have used the VST software package with the VST-III refractometer. It had a learning curve. There is no "..explicit connection between EY and flavor.." in the software as you put it.

From a prior discussion I had with you on the topic, you are still persisting in misunderstanding the terms and use of the tools.

The error is yours, not VST's.

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AssafL (original poster)
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#4: Post by AssafL (original poster) »

RyanJE wrote:Interesting post! So one part I personally dont understand....

"2. Associate EY statistics with grinder quality. EY statistics can and should be used to determine the quality of a grinder. An especially important optic into grinder performance is the need to WDT. If the output of a grinder improves by more than 1% after WDT - the normalization of the grinds is severely wanting. Examples: According to several tests Robur's (others) and Unaligned VL (mine) result in wider EY spreads (same coffee, same forumla) than a Mythos, aligned VL and a Monolith. Inconsistent results means the Robur is less able to control the density in the puck. "

I think its fairly common practice for people to WDT the monoliths. Does this imply quality issues with them because of the need to WDT? I am not sure I see the correlation of what you are proposing.
Well - the better a grinder is the less WDT needed. My Mini E needed a shaker. My Versalab at low speed hardly any.

The Brita Folmer book hints at normalization as a key factor in the performance of Nespresso capsules.

As to whether a specific grinder needs WDT or not is dependent on model and serial number and how well the user upkeeps the grinder aligned and sharp.
Scraping away (slowly) at the tyranny of biases and dogma.

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AssafL (original poster)
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Joined: 14 years ago

#5: Post by AssafL (original poster) »

nuketopia wrote:I have used the VST software package with the VST-III refractometer. It had a learning curve. There is no "..explicit connection between EY and flavor.." in the software as you put it.

From a prior discussion I had with you on the topic, you are still persisting in misunderstanding the terms and use of the tools.

The error is yours, not VST's.
Okay - errors are always on me. I love errors.

Sure. VST enables one to set a target target range. And a sophisticated user will do that. We all do.

But for a newbie, assuming the target is correct for his grinder, for his coffee, for his grind setting is tempting - and wrong.

Perhaps it isn't a tool for beginners? Maybe.
Scraping away (slowly) at the tyranny of biases and dogma.

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HB
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#6: Post by HB »

nuketopia wrote:From a prior discussion I had with you on the topic, you are still persisting in misunderstanding the terms and use of the tools. The error is yours, not VST's.
AssafL wrote:Perhaps it isn't a tool for beginners? Maybe.
Sigh. The subject of refractometers invariably leads to heated disagreements; I'm locking this thread for the weekend. Please take this time to review the site's Guidelines for productive online discussion, notably Be respectful and Encourage positive, shared discourse. Thanks.
Dan Kehn