cpreston wrote:Going back to the beginning of the thread, I had asked if 10+ degrees F variation in my kitchen would affect accuracy and got (helpful) responses that it shouldn't affect the refractometer reading . But what about the nominal 0.85 brix to tds conversion? Someone posted a chart showing substantial temperature sensitivity in that relationship. I would presumably get different tds in winter vs summer, no?

Also, would this affect only the Milwaukee? The VST as I understand it does the conversion internally.

All of the commonly available refractometers have automatic temperature compensation built in. With some, but not all, the user must perform a initial calibration manual calibration at room temperature and then the unit will be accurate across all credible room temperature variations. What gets missed is the sample should be cooled to close to room temperature or the results will also be off. For most cases coffee temperature will not be a source of significant error as long as the actual measuring techniques employed sample to sample are consistent.

Peppersass wrote: We're looking for the optimum extraction yield, where the coffee tastes best, which is not necessarily the highest extraction yield. There's only a narrow set of cases where higher is often better, and that's very light-roasted coffee. These coffees can be really hard to extract, and sometimes even when the %EY looks like it would be good (say, 20%), they still taste sour. Sometimes this is due to underdevelopment, but in some cases light roasted coffees taste better at high extraction yields that would make us spit out coffee extracted from a darker roast.

I have found extraction yield measurements to be very useful, but they're not the be-all and end-all of coffee preparation. They can be very helpful for beginners, can assist when dialing in, can help to maintain quality and can be very useful for troubleshooting. They can be tools of the trade. But they cannot substitute for evaluating taste.

I am on cool down for poor tone. And rightly so btw! So I only get one post a day right now;).

I would like to use that one post simply to thank Peppersass for coming back. This post was simply fantastic.

Blindly searching for higher EY% is absolutely not our goal. Learning how to use our taste buds in a consistent way to bring out the amazing qualities of each fruit is the goal.

I believe that, for the beginner, a refractometer is like a set of scales, or a timer, or a PID, or a distribution tool, or a trick tamper - an aid to help attain consistency - and that a more experienced/talented/skilled barista can be consistent without using scales, or a timer, or a machine with a PID, or distribution tools, or trick tampers, etc. None of these aids are necessary; they just make the process faster/easier/requiring less skills development. For example, one could say that someone who can cut shots by watching the stream (blonding) is more skilled than someone pulling shots using scales and timers; but this begs the question whether one wants to (eventually) become a better barista, or (just) consistently make a great cup of coffee. For the beginner, becoming consistent is paramount, as consistency is necessary before one can become proficient in using taste to dial in a coffee.

Peppersass wrote:... %EY has other uses as well: QA and troubleshooting. ...

These are great examples of refractometer usage that are beyond assisting attaining consistency on the handle side of the portafilter. For these uses, there are many arguments in favour of using more accurate/precise refractometers (and conversion algorithms). I had a Milwaukee; I found it inadequate for both of these uses simply due to only being able to display to 0.1 Brix.

I really like what Apogee has presented here. I also use a Milwaukee Brix refractometer for my espresso making and sometimes check with an optical instrument-- found remarkable correspondence in my readings. I find these measurements are fun to do and give me some information to think about AFTER I've sipped through my drink. As many have said here-- the important factor for consistency is to measure at room temperature. Research refractometers are routinely themostatted......

I've been impressed by how the tone of this thread has improved since the cooldown, and I think this thread proves that that feature has been a useful innovation on HB. With that said, here's my take on this issue, which is pretty close to Dan's.

Those who follow my roasting posts know that, when it matters, I am all about data collection in service of quality and consistency. Similarly, when I pull shots, I often keep track of dose weight, length of cooling flush (as a temperature proxy), beverage mass, and extraction time, aiming to pull a desired brew ratio each time. If my prep is bad, I'll know it because the shot will flow too quickly compared with other, comparable shots. I don't mess around with bottomless portafilters unless something is going really wrong, as I don't need to get squirted in the eye to know that a shot is flowing too fast.

Most importantly, I taste each shot (that is the point of the whole process after all). I've never bothered to measure extraction yield because I don't see how it would add to what I am already tracking. If a shot tastes bad, I adjust it based on taste. Early on, when I still didn't know much about what I liked, taste-wise, I would just try things all over the extraction spectrum to get a basic starting point, and make smaller adjustments from my best initial experiment to dial in balanced and repeatable shots.

Here's where I think most of the refractometry talk misses the mark, at least from the perspective of home users who can taste almost every shot they pull. Coffee might reach a target yield that is supposed to be good based on conventional wisdom or past experience, but still not be the best shot that I can make with that particular coffee. Without being able to adjust by taste, you cannot make these kinds of adjustments. And if taste judgments will always trump yield measurements, what value does it add to track the yields? Also, it has been noted in some recent discussions by talented pro-baristas who do play with refractometers that once you start varying pressure profile, starting temperature, or ground coffee temp, you can get very different tasting shots at the same extraction yield. So if you tie yourself to keeping everything but grind and extraction time constant and never exploring the broader space of variables, you will miss out on a lot of the possibilities that coffee has to offer.

In short, I think learning to listen to your palate (and learning how to make adjustments based on it) is one of the most important skills a new barista must learn, and I worry that too much focus on measuring extraction by other means than taste will delay that development.

OldNuc wrote:What gets missed is the sample should be cooled to close to room temperature or the results will also be off.

This is true. Precision refractometers are designed to operate in a fairly narrow temperature range that's close to typical room temperature. They'll work at temperatures outside the range, but the accuracy specs only apply to the designed temperature range. As I recall, improper cooling of the sample was one of the flaws in the first Socratic study.

To be precise, best results are obtained by equalizing the temperatures of the sample and the refractometer. Nominally, that's close to room temperature if the refractometer has been in the room for a while.

I let the cup sit for about one minute, then cool a few milliliters of the sample (filtered if espresso or press) in a heavy-bottomed glass for 30-60 seconds. Storing the glass with the refractometer helps to ensure they're at the same temperature. The ratio of the small amount of sample liquid to the mass of the glass ensures rapid cooling, and swirling the sample in the glass speeds up the cooling even more. Then I place 1-2 ml of the sample the refractometer window, close the cover and wait another 30 seconds for the temperature to equalize.

Good point about consistency. Always use the same sampling procedure.

[creative nickname] wrote: It has been noted in some recent discussions by talented pro-baristas who do play with refractometers that once you start varying pressure profile, starting temperature, or ground coffee temp, you can get very different tasting shots at the same extraction yield. So if you tie yourself to keeping everything but grind and extraction time constant and never exploring the broader space of variables, you will miss out on a lot of the possibilities that coffee has to offer.

Apogee Technique

3) Set temperature to 200 and don't change it*

[Creative Nickname] is absolutely right; Pro-baristas open up the variables of pressure and temp to bring out the flavors they wish in their coffee.

I would love to start an "advanced refractometry" thread with the help of you all, when I get there (or have Peppersass write it now!). Focused on opening up new variables with refractometry, and assuming a heightened sense of taste and routine consistency (gained from beginner's refractometry) to bring out the best in each fruit varietal. Getting past my pay grade here...

I will just mention as softly as I can, this thread is for beginner's learning how to brew by taste and feel by using a refractometer to help us fix our technique and differ between under extraction and over extraction. Then differ between over extraction and a dirty machine. Then differ between good roasters and bad roasters. Then differ between young, peak and past peak post roast aging. Then...insert other basic thing you all have wonderfully and amazingly at times developed.

I'm going to share my experience that varying grind and/or pressure and/or temperature and/or shot time to change EY% and TDS% (to meet the beginner's first goal: 19.5g dose(20g VST, 1:2 BR(brew ratio dose:beverage), 20 EY%, 9.65 TDS% and nail it every time); and in parallel, brewing better tasting espresso was an absolutely overwhelming group of tasks to me and it only had me think there was magic because all of those things were changing. It had me drink Keurig.

My name is Apogee, and I drank 3 cups of Keurig "Dark Magic" everyday for 3 years. I want to thank you for listening.... I needed help. Bad.

Apogee technique: lock temperature at 200, test it and don't change it, lock pressure at 9 bar, test it and don't change it; lock shot time at 28-32 (shot yield takes priority, test it and don't change it, review Perger's great work on dosing, yield and time); and...

ONLY CHANGE GRIND for now I ask as a beginner. It is "the VARIABLE" (Step 5). Even I can change grind. I can do 1 task right!

Thank you again to the comment quoted above. It is an excellent post and I, personally, aspire to bring those additional variables into my technique...but not yet.

Forum member SlowRain is teaching me patience;) Namaste

Apogee wrote:I am on cool down for poor tone. And rightly so btw! So I only get one post a day right now;).

I would like to use that one post simply to thank Peppersass for coming back. This post was simply fantastic.

I always like to see and enjoy the Love, Harmony and respect to each other in this forum


Behold, how good and pleasant it is
when brothers dwell in unity!
It is like the precious oil on the head,
running down on the beard,
on the beard of Aaron,
running down on the collar of his robes!
It is like the dew of Hermon,
which falls on the mountains of Zion!
For there the LORD has commanded the blessing,
life forevermore.

4) Pre-infusion: Set a long, reduced pressure preinfusion for 7-10 seconds and dont change it*

Pre-infusion lets me grind finer and achieve a higher EY% and TDS% up to a point.

I tested none which results in more frequent channeling, I tested longer than ten seconds with no benefit; so I found 7-10 seconds gave me the best EY% and TDS%. I believe this is because whenever I nailed a shot, on my machine, drips would start coming out at 8-11 seconds; I believe this may be machine specific. Matching pre-infusion to this natural machine timing does not seem unwise in retrospect.

Anyway. You try different levels of pre-infusion and test it, and then don't change it.*

Haha i got it in yesterday but don't have any coffee espresso worthy at the moment. May just have to make due tomorrow anyway:)