Espresso Brewing Control Chart - Page 2

Beginner and pro baristas share tips and tricks for making espresso.
King Seven

#11: Post by King Seven »

Would be interesting to see the difference between refractometer and baked puck data, to see if there is some sort of correlation between the two, to allow you to factor in accurately what you might not be able to see with the refractometer?

gscace

#12: Post by gscace »

What I should have done while I was there was to pose that question directly to George Howell and his minions to see if they had the data and if they had thought it through. I suspect one still could do so by phone.

-Greg

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another_jim
Team HB

#13: Post by another_jim »

Iirc, Andy did some experimenting along this line several years ago and got a strong correlation between the refractometer readings and the baked puck data. So the refractometer readings, properly scaled, can be used as a measurment of extraction. However, there wasn't enough of a data set to determine whether the correlation was unaltered when using different coffees, baskets, grinders, etc. Worst case, the refractometer readings need to be scaled differently under different conditions.

I'm not sure how much data Vince collected, and whether a peer review would pass on his scaling algorithm. When I first heard about it, I was personally loath to take on the job of collecting a dataset large enough to create a sound conversion table (for instance, I doubt the SCAA did enough in the 50s for their conversion from conductance to yield to be sound, their raw data never saw the light of day, nor did it make it into a peer reviewed article)

On the other hand, in a shop environment, a conversion table is not necessary. Suppose the refractometer (or conductance) reading is monotonic with the solid + solubles concentration in the cup. That is, reading = function(solids + solubles) and the function is invertible. Let the inverse be S(*) the unknown scaling function that converts the reading back to the concentration. This scale is monotonic, and can be treated like the actual measurement in arbitrary and unknown physical units. Like units of old, they can be different from coffee to coffee and shop to shop, but within a tight context, they work.

Basically, one can, for every setup (grinder, blend, baskets), take refractometer readings and divide them by shot weight to get this arbitrary but accurate extraction measure. One can therefore reliably use it to learn how that measure changes when changing dose, shot time, etc., and which extraction level tastes best. One can then spot check that the same extraction value is being maintained in operation. This is no different than what one would do if the scale was correct.

So I think Vince's system can work whether the scale is correct and transferable or not, as long as it is consistent in any one setting. On the other hand, the same can be said for a $30 brix meter on its own. The software also has convenience and administrative tools; and for a cafe that may make it very worthwhile. I'm less sure if these extras' are valuable in a home setting.

Personally, since there are many brix meters available with a wide range of costs and features, I would prefer if we used raw brix and brix*shot_weight/dose_weight readings to communicate concentration and the extraction measures. That way we can compare notes, and discuss possible conversion algorithms in the open context of scientific discussion. If we use the Terroir system while it is unpublished, we are using something that seems very odd to me, a physical unit which is proprietary and trade secreted.
Jim Schulman

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Elbasso

#14: Post by Elbasso »

While reading up on refractometers I got slightly confused about Brix. Wikipedia states: Degrees Brix is a measurement of sucrose in a liquid. Is the Brix mentioning in this topic therefore misplaced? Or does it correlate to brewing ratio somehow?

CHeers,

Bas
Creativity is the sudden cessation of stupidity.

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another_jim
Team HB

#15: Post by another_jim »

On "brix meter" refractometers, the most common kind, the refraction angle from the refractometer is converted into a brix reading, which is the amount of dissolved sugar in the liquid. The amount of dissolved sugar will be directly proportional to the amount of total solids that get into the cup for a given coffee and brewing method. Whether it is the same proportion for all coffees and brewing methods remains to be seen. Since the amount of sugars in coffee varies by varietal, region and degree of roast, I doubt it.
Jim Schulman

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AndyS (original poster)

#16: Post by AndyS (original poster) »

gscace wrote:I asked Barry (Jarrett) about this system at the show....
Greg: Of course a refractometer measures only dissolved solids. That does not mean it cannot be used to derive excellent results in measuring espresso solids yield.

Sorry guys, I don't have time for a long post now. But this weekend I will try and furnish some actual data to try and balance the mix of misinformation and wild speculation that has suddenly appeared in this thread.
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

gscace

#17: Post by gscace »

I confess to being pretty ignorant, for sure.

-Greg

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AndyS (original poster)

#18: Post by AndyS (original poster) »

gscace wrote:I asked Barry (Jarrett) about this system at the show because I was sorely tempted to part with the money. Barry said that the refractometer didn't measure non-soluble components and that non-soluble components account for a large part of the espresso experience.
Has Barry actually compared results obtained from dehydration to those obtained using accurately calibrated refractometers? I doubt it.

Perhaps non-soluble components account for a large part of the "espresso experience", but that doesn't mean they're a large part of the extracted mass; Illy says that masswise the insolubles comprise about 10% of the total. This is a small enough part of the whole that the method will be pretty accurate even if the solubility varies.

[Say you had two coffee that were very different, so that the insoluble fraction was 8% for one and 12% for the other. And say the refractometer scale, which uses only the soluble portion, returned a 20% total solids yield for each one. They would still be within 1% of each other if the total extracted solids were measured by dehydration. That's good enough to hit the sweet spot.]

Greg, the use of refractometers for brewed coffee has tons of science behind it, and Terroir has extensively tested their instrument and software to measure it. The brewed coffee refractometer is the one that was for sale at the show.

The use of refractometers for espresso is still in the early stages. There are only a handful of the Terroir-calibrated espresso instruments in existence. They won't be ready for distribution until June at the earliest. But so far they seem to be operating well. I recently did several rounds of tests comparing dehydration to the espresso refractometer and Vince at Terroir did a bunch in Boston. The refractometer technique takes care, and therefore it's not infallible, but believe me, dehydration testing is not infallible either.

Below is a graph showing total solids yield derived three ways: drying the puck, drying the espresso, and using an earlier version of the Terroir Espresso Refractometer. There are some weird outliers, but in general the agreement is very good. Below that is a chart showing the actual data. ["nD" stands for refractive index, IOW, the refractometer reading]





-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

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AndyS (original poster)

#19: Post by AndyS (original poster) »

another_jim wrote:On "brix meter" refractometers, the most common kind, the refraction angle from the refractometer is converted into a brix reading, which is the amount of dissolved sugar in the liquid. The amount of dissolved sugar will be directly proportional to the amount of total solids that get into the cup for a given coffee and brewing method. Whether it is the same proportion for all coffees and brewing methods remains to be seen. Since the amount of sugars in coffee varies by varietal, region and degree of roast, I doubt it.
Wrong, wrong, wrong, wrongity wrong.

"Brix Refractometers" read the change in density resulting from ALL the dissolved components in solution, not just sugar. They are calibrated to read % sugar, but this calibration is accurate only for sugar solutions, and obviously, the solubles in coffee are NOT pure sugar.

In addition, since refractive index varies with temperature, Brix Refractometers are often "temperature compensated" to give accurate results over a reasonable range of temperatures for sugar solutions. Since the curve of refractive index for sugar solutions vs temperature is different from the corresponding curve for coffee solutions vs temperature, errors can be introduced when brix instruments are used for coffee. A "Coffee Refractometer" or an "Espresso Refractometer" is programmed with temperature compensation curves different from those appropriate for sugar.
another_jim wrote:Personally, since there are many brix meters available with a wide range of costs and features, I would prefer if we used raw brix and brix*shot_weight/dose_weight readings to communicate concentration and the extraction measures. That way we can compare notes, and discuss possible conversion algorithms in the open context of scientific discussion. If we use the Terroir system while it is unpublished, we are using something that seems very odd to me, a physical unit which is proprietary and trade secreted.
The "Terroir physical unit" is not proprietary or "trade secreted." On the contrary, the coffee instrument reads TDS (total dissolved solids). The espresso instrument (under development) reads TBS (total brew solids, ie, dissolved + undissolved solids).

These are NOT proprietary measurement units, they are exactly the everyday units that we need to do this work.

If you are skeptical that the Terroir refractometers work as advertised, you could buy or borrow one and run your own dehydration comparison. But to ignore the logical measurement units that have been around for 60 years, and propose a new standard measurement using brix, is a huge and totally unnecessary step backwards (IMHO).

P.S. The technology that makes the Terroir instruments work IS proprietary, but I guess once the patents are published (late this year?), you'll be able to read all about it.
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company

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another_jim
Team HB

#20: Post by another_jim »

Andy, you're absolutely right on the refractometer and the units, but I'm not ready to concede my main two points, which are:

-- The consistency of correlation of refractometer readings to solids concentration and extraction is not known. Your data are a start, but it'll take data from a variety of settings to get some certainty. Pure noise is less of a problem, since that can be dealt with by doing multiple readings (good practice in any case, since there's always operator error, and a huge plus for a simple, non-destructive method like the refractometer over puck baking). I'm more concerned with systemtic errors due to different conversion constants for different coffees, grinders, baskets, etc.

-- The conversion that Terroir uses is unpublished. Until it is, it would be better to communicate with the most widely available units, e.g. brix for refractometers and CaCO3 concentration for conductivity meters.

These points are temporary. More testing will reveal the method's limit conditions, and a patent application will state the conversion algorithm.

BTW, while algorithms are patentable, a patented conversion algorithm may not be much protection. Anyone who has college algebra can do a Taylor expansion of the algorithm for the numerical range of interest, then use any equation that has the same expansion for that region as the "new improved" conversion algorithm.
Jim Schulman