STRONG COFFEE strongly believes that for the best tasting cup of coffee, you should skip the sugar/milk and go straight for the SCIENCE. Today our dollop of SCIENCE will be assisting us in our quest to make the perfect cup of coffee by using the refraction of light to discover the perfect extraction.
“What makes coffee taste great is the ability to trap both available solids from the ground coffee and escaping volatile gases into a liquid state, so that when you drink the coffee, your nose and tongue work in concert to provide you a memorable experience.” In order for our coffee concert to rock your face off, we need to make sure our extraction is in tune.
By definition, extraction (in chemistry) is a process consisting in the separation of a substance from a matrix. In our case, the substance is drinkable coffee and the matrix is ground coffee. Water moves into the coffee particles, it dissolves or suspends different substances and extracts them from the solids. Hot water also cooks as it extracts, forcing chemical reactions that transform some of the substances into other things. Once the desired amount of solubles have been dissolved in the water, there needs to be a balance of that coffee flavor to the liquid that completes the cup. In most instances, it will ideally be less than 2% coffee solubles, and more than 98% clean hot water.
When coffee is under extracted you get a sour and/or grassy cup. When it’s over extracted it will taste bitter. In fact, Starbucks found that it can use 20% less coffee by grinding finer and overextracting which you may have noticed has caused their coffee to taste more bitter. Damn you Howard. With so many variables (water temperature, grind size, brew time, agitation, coffee/water ratio, water profile, coffee density, roast level) how are you supposed to know when you have achieved proper extraction? Please welcome SCIENCE to the stage. SCIENCE will be playing the refractometer.
A refractometer is a device used for the measurement of how light, or any other radiation, propagates through that medium. “A coffee refractometer includes a prism that receives a brewed coffee sample, thus forming a prism-sample interface. A processor or microcontroller controls a light source to provide incident light to the prism-sample interface. The prism-sample interface refracts light toward a photodetector. A temperature sensor provides temperature information to the processor. The refractometer includes a memory store that stores a TDS (total dissolved solids) formula that expresses the TDS of brewed coffee as a function of the index of refraction of brewed coffee and the temperature of brewed coffee. The processor determines the TDS of the brewed coffee sample by accessing the TDS formula in the memory store and employing the determined index of refraction of the brewed coffee sample to find the TDS from the TDS formula. The refractometer displays the resultant TDS % on a display of the refractometer and/or transmits such information to an information handling system.” Until recently this super geek toy would of cost you upwards of $10,000.
Thankfully VST Labs has released what they call ExtractMojo. ExtractMoJo is, very simply, a refractometer paired with the universal brewing control chart. In essence, the chart provides a graphical representation of strength, extraction and brew formula in an easy to read format.
So basically you brew your coffee, take a sample, shine some light through it and you get a number. When you plug in the number along with the amount of water and coffee grinds, it tells you the brew strength and extraction yield. By plotting those on the chart, you know whether or not you’ve brewed a decent cup of coffee. The ideal range is between 1.2 and 1.55 percent. A app called MoJoToGo even repackages the ExtractMojo software into an iPhone app.
At the end of the day, the refractometer can only tell us what percentage of the material was dissolved, not what type. Even if the extraction shows to be perfect, it does not mean that we extracted the right soubles. Or at least ones that we prefer taste wise. In our opinion, you should always shoot for the top middle section of the chart and DRINK STRONG COFFEE.