mitch236 wrote:I don't blame you!
I wonder if you could explain exactly how use the results to change your brew parameters? I have one one on order but haven't played with it so am not sure how it fits in with my workup routine.
Before we go down the rat hole on this, I would ask everyone to re-read my post over on CG. I spent a great deal of time wording it. I wanted to be as clear as possible about what the device is and is not, and how I use it. I did not say the VST Refractometer is something I use on a daily basis as a tool for pulling shots, like my 0.1g scale, which I use (twice) for every shot I make.
As I said, I use my VST Refractometer primarily when dialing in a new coffee. In that endeavor, I'm experimenting with different grind settings, doses and temperatures, so I find it very useful to follow the extraction yield as I vary those parameters. My expertise in this is less than the more experienced home baristas on this site, so I'm less able to do it by taste as well as they do. Also, as I mentioned, it's easy for the tongue to get overwhelmed by strong flavors during a dialing-in session, at which point it's easy to get confused about what I'm tasting and which direction to go. Taste memory is notoriously unreliable, at least for me, and it's easy to forget what something tasted like in the time it takes to prep the next shot. The refractometer provides an unbiased number that can help me cut through the taste confusion.
Of course, I can detect extreme flaws. Heck, the flow rate often tells me all I need to know. I've certainly spit out my share of sink shots, too. But as I approach the sweet spot, and the differences get a little more subtle, it's great to know if I need to grind a little finer or a little coarser, bump the temperature one way or the other, etc. Once in the 18%-20% range, it's useful to move around in that zone to explore the range of flavors, using the refractometer to make sure I know where in the range the drink landed. This is not an ultra-precise process because the extraction yield varies with what we've all come to know as "shot-to-shot" variation. If you plot multiple pulls, the extraction yields won't be exactly the same, but will cluster around an average value.
For this reason, as I said on CG, you can't use the refractometer to adjust for subtle nuances. The instructions for brewing Tchembe 90+ on the Compass Coffee site come to mind.
. Here they make slight tweaks to the brewing recipe to bring out different flavors. I haven't tested this in depth yet (just got a couple of bags in), but I'm skeptical that the refractometer can assist in something like this. If pulled properly, both recipes will end up close to or in the 18%-20% zone. I don't think you can use the refractometer to pinpoint the exact crossover point, unless the yield percentages are widely separated at either end of the scale. If they're too close together, shot-to-shot variation will swamp the data. Your tongue will be your only guide at this point, but at least the refractometer will continue to confirm whether or not you've stayed in the optimum zone, and will tell you which direction you've moved the extraction.
My post also refers to using the VST Refractometer to diagnose extraction flaws due to factors like coffee aging, roasting faults and equipment problems. Although my data on this is incomplete, I happened to notice an increase in extraction yield when I switched from an Everpure Claris system back to my old cation system. One difference between those systems is that the water from the cation system has considerably higher %TDS (about 150 ppm versus about 80 ppm.) Previously, I had noticed that shots pulled on my espresso machine tended to be at the bottom end of the sweet spot or slightly under extracted. It was actually difficult to over extract shots. Meanwhile, coffee brewed on my Technivorm could be varied all over the range from horribly under extracted to horribly over extracted. The difference was that the espresso machine was being fed by the Everpure system, while the Technivorm was using unfiltered tap water (%TDS, hardness and alkalinity all in the 150-180 ppm range.) I need to do more work on this, but it's possible the refractometer can be used to determine the impact on extraction of varying mineral concentration in the water.
I should also point out that, as a home barista with only 2 1/2-years of shot-making experience, I have found the VST Refractometer, and the PC/iPhone software to be excellent learning tools. While Jim has taken great pains to explain what governs taste in espresso preparation, for me seeing the results in the form of numbers has been a great help. For example, prior to getting the device, I was confused about the roles played by the grind and the dose in determining flavor. Some of the advice posted here has been hard for me to understand. With the refractometer, I quickly learned that grind and flow rate determine the balance of flavors, while the water ratio (amount of coffee / amount of water) determines the strength. These things interact to form the thing we call taste, but the way in which they do has become much clearer in my mind since I started making extraction yield measurements.
One thing that really surprised me was that I could vary shot time within a certain range and the extraction yield would be about the same. For example, let's say I dial in a 14g normale at 30 seconds to produce an extraction yield of 19%. Once I get that recipe down, I can produce a ristretto by cutting the shot short by say, five seconds, or a lungo by letting it run five seconds longer. The extraction yield doesn't move much, but the strength of the coffee does. I'm just holding the amount of coffee constant and varying the amount of water and contact time. My understanding is that this is how they produce ristrettos and lungos in Italy -- they don't vary the grind or dose, they vary the shot time. Note that there's a somewhat narrow range where this works. If you get too far from the center, under extraction or over extraction can result.
To reiterate the original point, once I'm done dialing in, the refractometer goes back in the drawer. Assuming I've dialed in successfully, my tongue is more than adequate for determining whether the extraction meets my expectations. My equipment is so consistent and so reliable that shots rarely depart from expectations in a big way, unless I make a preparation error (usually quite visible, even with a spouted PF, via altered flow rate, shot time, extraction color, etc.), or (rarely) the coffee is nearing the staling point or ambient humidity has drastically changed. I usually know what to do to correct the shot, which is usually to do it over again more carefully. On rare occasions, the anomaly persists, and that's when I pull out the refractometer.
Before I forget, there's a clarification I need to make: In different places here, I've referred to the device as the VST Refractometer or just "refractometer". Although I've used the latter term for convenience, there's an important distinction. The VST product is much more than just a measurement device. I have found the ExtractMojo program and MojoToGo app to be very useful analytical and learning tools. They've been a big part of clearing up my understanding of coffee extraction, and they are of great help in evaluating recipe variations. I'm sure I would be lost if I had just an instrument that reported the refractive index or even just %TDS. The calculations performed by the software, the dynamic extraction chart, the ability to vary the computational parameters, and the ability to evaluate different recipes are all features that I consider an integral part of the VST system.
In conclusion, while I feel the refractometer is an excellent tool for dialing in and diagnosing extractions, and is a great learning tool, I do not see it as something one would use on every shot. Given the measurement process, that would be completely impractical and counter-productive (the ultimate goal is to enjoy the coffee!) I also think the value is quite limited for anyone who does not have reasonably consistent espresso equipment. You can't learn anything about varying extraction parameters if your grinder is putting out a different particle distribution on every grind or you can't return to a particular grind setting and get very close to the grind you had before. The refractomter will tell you that the extraction yield changed, but you won't know whether it's your technique or the equipment. I suppose if your technique is good, the refractometer will be able to quantify for you just how inconsistent your equipment is.
I think the home-barista sweet spot (no pun intended) for the VST Refractometer is the owner of medium-to-high end equipment who can afford to spend the money, has the passion to invest in espresso, wants to learn more, and may not necessarily have highly-refined cupping abilities (yet.) If I owned a cafe, I would definitely use a VST Refractometer for dialing in, barista training, quality control and troubleshooting. Also, similar to a Scace Thermofilter, it's very appealing to lab-equipment junkies and sticklers for accuracy like me
[EDIT: Seeing as how the discourse has been so congenial, I have changed the title of this thread. Let me add that I have no affiliation with VST, other than as a customer.]