Posted Thu Mar 1, 2012, 12:32am Subject: Re: coffee refractometer
I don't know your situation vis-a-vis your need for a grinder, but I can say that I've been very pleased with my VST LAB Refractometer, ExtractMojo PC program and MojoToGo iPhone app. I'm a customer, not a beta tester, so I can give you the consumer perspective. I second everything Andy has said about the instrument and software. The instrument is exquisitely made, a true piece of lab gear. It's easy to use, easy to clean and extremely rugged. I'm satisfied that it's more than accurate enough for my needs, and it has been very helpful both as a learning tool and as a frequent aid in coffee preparation.
The unit I have measures %TDS only, not refractive index as Andy said (maybe he has an earlier version.) But I don't need the refractive index because my interest is solely in using the refractometer to explore coffee extraction, so %TDS is the measurement value I need. The ExtractMojo and MojoToGo software both take %TDS as input and compute the all-important extraction yield based on the dose, water volume and other factors, which is the number I'm really after.
As Andy says, the PC program has many adjustable parameters that allow you to customize the calculations and work out doses and water volumes for various applications with both brewed coffee and espresso . I've learned a lot just changing the parameters and watching the effect on the extraction chart. The iPhone app is ideal for quick computations and recipe storage/reference at the coffee bar. I strongly recommend the PC app, but if you spend a lot of time in front of your coffee equipment pulling shots and brewing, you'll eventually want the iPhone app, too.
I've had the products for about five months. I use them whenever I'm preparing a new coffee for the first time. I've also run measurements when I've encountered unexplained flawed extractions, and in several cases have been able to use the information to determine the cause. For example, I had gotten into the bad habit of not resting my freshly roasted espresso beans long enough, and was able to see from the changes in extraction yield over time just how much rest produced the best results. I was also able to confirm that properly freezing and thawing coffee hasn't negatively impacted flavor, though staling progresses more rapidly after thawing. And in one instance I was able to confirm a flawed roast on the part of a roaster, possibly due to persistent bad weather at his location. Very cool stuff.
While I use the system mostly for espresso, it's been quite helpful to me in making brewed coffee in a Technivorm MocaMaster I got for my birthday last fall. I've spent a great deal of time over the past three years learning to make espresso, but I really don't know much at all about optimum grind, dose and extraction time for drip coffee (despite making hundreds of mostly bad pots of the stuff over my lifetime.) The VST refractometer and ExtractMojo have been very useful for establishing a general recipe and range of grind settings that work well for the equipment I use and the coffees I drink, allowing me to judge the effects of various tweaks in preparation (dose, grind, steep time, stirring grounds during steep versus not stirring, etc.) In most cases, the effects on extraction yield are readily apparent. My next project will be to use the VST Refractometer to explore recipes and techniques for the two vac-pot systems I have.
Of course, taste is the final arbiter, and I'm sure VST would heartily agree with that statement. I can certainly taste when an extraction is well balanced or has gone awry. But my ability to precisely identify the flaws, and figure out what to do about them, isn't all that great. Maybe it's because I'm not a trained cupper. Or maybe it's really hard to do: tasting is a highly subjective process, and once you start assaulting your taste buds with strong espresso, your sense of taste quickly gets saturated and is less effective at detecting nuances. The repeatability and total objectivity of the refractometer make it a valuable adjunct to my taste evaluations. I certainly wouldn't use % extraction yield in lieu of taste for deciding if an extraction is good or not, but it's a valuable piece of information for understanding what the extraction has produced and how it might be improved.
Further, the refractometer isn't going to correlate things like "wild blueberry notes laced with milk chocolate overtones" with a precise %TDS or extraction yield. There's not enough precise repeatability in coffee making to do that. What it will do is let you know when your recipe gets you into the zone of extraction yield that has been proven to balance flavors best and please a broad spectrum of coffee drinkers (generally 18%-20%.) Most likely, that's the range where the subtle and interesting flavors of single origin coffees will present themselves, though tweaking the extraction within the optimum range can change the emphasis (I'm primarily talking about espresso here, where small changes can make a very big difference.)
I've taken detailed notes on all my extractions measured with the VST Lab Refractometer, and have been planning on writing a comprehensive review of the products and my experiences with them. Unfortunately, the real world has sucked up a great deal of my time in recent months, so I haven't gotten to it yet. I hope the brief description above is helpful in the meantime. Feel free to ask questions.
mitch236 Senior Member Joined: 7 Nov 2003 Posts: 64 Location: Delray Beach Expertise: I love coffee
Espresso: Linea Single Group (PID,... Grinder: Mazzer Robur E
Posted Fri Mar 9, 2012, 11:34am Subject: Re: coffee refractometer
I received my refractometer about 4 days ago and found out something very interesting. I've been struggling for quite some time trying to get my shots to taste right. Now I know exactly why my shots rarely taste great. I am chronically underextracting. As to why this is happening is now under investigation but I think this points to one of the greatest features of the device. Unless you have one of the "golden tongues" come to your house and help diagnose your extraction issues, you probably are chasing your tail. This device has the ability to diagnose issues very quickly and help you overcome them. Even if you don't subscribe to the notion that a shot can be dialed in with a refractometer, you should realize this tool is invaluable as a diagnostic device capable of saving endless hours of frustration. Also, unless you've been to one of the top cafe's, you may not even know what a great shot should taste like.
Since my setup underextracts no matter how I try to manipulate it comes down to one of two issues: Either my water has too low TDS (it is 50 ppm) Or my machine's pump pressure is too low (it is currently set just below 9 bar by the integral pressure gauge which could be wrong)
I'll know the answer to the pressure issue tomorrow morning. The water TDS issue will be dealt with in a few weeks.
Bottom line: If you can easily afford one, get it. Yes, I've heard the complaints about the filters being expensive but in the grand scheme a dollar isn't really much money. Yes, I've heard it is tedius to perform the measurements. That's true but not as bad as it sounds. If you can't afford to buy one, try like heck to rent one. I don't know if rentals exist (mine is NOT for rent) but ask around. For me, this device has proven to be invaluable.
Posted Fri Mar 9, 2012, 3:56pm Subject: Re: coffee refractometer
First major check is a dehydrated beverage/spent grounds check. Prolly get to it tonight or tomorrow morning.
I plan on brewing 22.0g of coffee in the Aeropress, 230g brew water. This should yield 200g of coffee, give or take. I'll be using a paper filter. If the extraction is correct, the brew should be around 2.2% strength, and I plan on recovering about 4.4g of solids when the beverage is dehydrated, and the remaining in the dehydrated spent grounds (17.6g)
Sounds good. I always had trouble knowing when the grounds and/or beverage were properly dehydrated. And I found it disconcerting to watch the masses spool up on the scale as they regained moisture from the air. But you seem to have worked it out. Again, I'm looking forward to your results.
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