An iPhone App, a Refractometer, an Objectively Perfect Cup of Coffee

By Jennifer Welsh | September 20, 2010 4:58 pm

coffee---flickr-user-roreA new iPhone app, linked with a refractometer and decades of coffee science, can help you brew the perfect cup, for only $350. Don’t believe that such a thing is possible? Gizmodo sums up the natural inclination against believing that science can tell us what tastes best:

People accept scientific measurements as the truth about a lot of things. Mass. The temperature at which water freezes. The size of the earth. But it’s hard to swallow the idea of scientifically measuring how something tastes. Taste is subjective. Right? Not anymore—thanks to MoJo, a gadget that quantifies a cup of coffee’s flavor.

And while some people might spend outrageous amounts of money on that perfect bean, Vincent Fedele tells Gizmodo’s Matt Buchanan that “most of us blow it in the last 5 minutes”—i.e., improper brewing.

To tell the difference between good coffee and the bad, most coffee specialists refer to Scott Rao’s book Everything But Espresso. The best cup of coffee, as determined by chemist Ernest E. Lockhart and the National Coffee Association, has two important numbers. The first is the brew’s strength, or total dissolved solids (TDS) of 1.2 – 1.55 percent. The second important, defining number is the brew’s extraction rate, the perfect brew extracts only about 18-22 percent of the flavor from the bean. Getting both of these numbers in the correct range can be difficult:

It’s a remarkably tiny spot to hit. But uh, how do you get there? If the brewing control chart is a map, ExtractMoJo and MoJoToGo are the GPS. ExtractMoJo is, very simply, a refractometer paired with the universal brewing control chart, an updated version of the original chart from the 1960s. MoJoToGo repackages the ExtractMojo software into a super-handy iPhone app.

The refractometer determines the speed of light moving through your coffee, and therefore its concentration. The computer- or iPhone-based software can tell you the TDS and the extraction rate of your cup based on that concentration number and the amount of water and coffee grinds that went into the cup. Plotting these numbers on the Universal Brewing Control Chart tells you how good or bad your cup will be.

But the application, combined with an obsessive personality, could lead to disaster, judging by what’s happened to Buchanan:

I tear through a $16.50 one-pound bag of coffee in about three days, making coffee over and over again, seeking the mythical number 19. I use a version of the French Press technique from Everything But Espresso. Start the kettle. Weigh the beans. Grind the beans. Wait for the water to reach 206 degrees. Pour 400g of the heated water onto the grounds. Start the timer. Pat the coffee bloom. Dunk the coffee bloom. Wait 4-5 minutes. Plunge. Pour. Check result in MoJoToGo. Curse.

Related content:
Cosmic Variance: Making Coffee
Cosmic Variance: Coffee Rituals
Cosmic Variance: The Science of Coffee
Discoblog: What Happens When a BP Exec Spills His Coffee–and More Cathartic Comedy

Image: Flickr/rore

  • greg

    But the whole MojoToGo thing represents everything misapplied about science. Subjective things like taste can be partly measured, but it’s sheer idiocy to believe there’s a numerical formula to unlock the “perfect” coffee — despite years of Martha Stewart espousing the virtues and accessibility of “perfect”.

    Good coffee has a lot of science that is not acknowledged relative to its supposed art. But it is cynical efforts like this, poised to profit from the “perfect” mantra emanating from food TV saturation, that confuse the pedestrian act of measurement for honest science.

    If measurement were science, we’d have Nobel Prizes for weathermen.

  • Jennifer Welsh


    I don’t know about you, but I would still like to try a cup that lands in that “perfect” area instead of my usual street-cart brew. Maybe I’m just an unsophisticated coffee brute!

    Thanks for reading and leaving your opinion!


  • Mark

    Okay, I’m interested in knowing more about Buchanan’s results, eg – a scatter plot of the results of the attempt to hit the 18% – 22% range. You know, the basic range, mean, mode mantra.

    Or, if he’s not that careful, (anal?), of a note keeper, at least an idea of how consistent his results might be. Consistency and only having one dependent variable might help.

    And, I’d assume that he at least tasted the results of his efforts; what were his beliefs in how it tasted?

    At first I feared I was going to have to switch to an iPhone, refractometer and this app, but now I think I’ll stick with what my own taste buds tell me and not get into another endeavor that will test the strength of my marriage.

    Thanks, Jen, for the great reporting.


  • Jay Warner

    Mr. Buchanan probably does need to tighten up his experimental methods. Restricting to 2 or 3 variables, for one thing, and _carefully_ performing a properly designed experiment (DoE) That’s what a DoE is – preplanned testing with interpretable results. I would also urge him to take two response (outcome) measures – one his magic number of 19 [units?], the other a taste test of some kind. It is harder to quantify ‘taste,’ but some people do it for beer already, on two or three axes (variables). Surely coffee experts do as well.

    To encourage Mr. Buchanan, I report development, through suitable experimental methods, of a ‘perfect’ recipe for baking bread in a bread machine. It’s not a kind available in a recipe book, it comes out within a narrow range of size and quality almost every time, and it flexes enough to predict recipes for slightly alternate types of bread. Mr. Greg (9/21, 2:46 pm) probably wouldn’t understand.


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