BeanScene Magazine

I recently had the privilege of representing Australia in the World Brewers’ Cup, a competition in which participants are asked to brew three cups of coffee and scores are awarded almost entirely based on cup quality. This year, the event was held in Maastricht in the Netherlands and in travelling there, I encountered the same question that many of us have faced at one time or another: how to brew coffee while travelling. 

There is a variety of brewing equipment that is small, cheap, easy to use and easy to clean up after; qualities that also make such equipment ideal for home use. The weak link in the chain always seems to be the grinder. Conventional wisdom has it that you should always avoid pre-ground coffee and buy the best (and therefore, perhaps, the biggest) grinder that you can afford. Like all conventional wisdom in coffee, it should be verified by blind tasting.

For this experiment, I was joined by Market Lane Coffee’s director of coffee, Jason Scheltus for a blind tasting of the same coffee prepared using different grinders.

A Quick Recap: Brewing Ratios

So how do you go about comparing grinders in a fair manner? After all, how can you be sure that taste differences between grinders are due to the differences between the ways in which those grinders grind coffee rather than grind settings?

The answer to this question lies in research that dates back to at least the 1950s and that forms the basis of the “Gold Cup” certification programs run by the specialty coffee associations of Europe and America. An exploration of the history of the program is beyond the scope of this article, but if you are interested I would heartily recommend reading the book Uncommon Grounds by Mark Pendergrast.

In essence, brewed coffee can be quantified in terms of strength and extraction. Strength refers to how much of the brew is made up of dissolved coffee and is usually expressed as a percentage of total dissolved solids (TDS). Extraction refers to the percentage of the mass of ground coffee that is dissolved in to the water. The two are related by the equation: (Extraction (%) x Weight of Coffee (g))/Water (g) = Strength (%). If all variables except for extraction are identical between two cups, the extraction percentage must also be identical.

However, this doesn’t tell us about the taste of the resultant cups because even though the amount of the compounds extracted from the ground coffee might be the same, their nature might be different. It is speculated that this difference could arise because different compounds have different solubilities in water, which means that, in theory, different grinders could produce different cups at the same TDS because of the grind profile produced by those grinders. The upshot of this is that I feel it is useful and practical to compare coffees extracted from different grinders dialled in to produce the cups of the same TDS.

Measuring Total Dissolved Solids

TDS can be measured directly by devices that can read out physical properties of brewed coffee relating directly to strength. The two main commercially available TDS meters measure the conductivity of the brew solution or the angle at which it refracts light. The United States’ Voice Systems Technology Inc. has recently focussed on popularising the use of refractometers in combination with its ExtractMojo software.  For this test’s purposes, I used the VST Lab refractometer, which I found much more useful than the standard Reichert refractometer sold by VST and certainly worth the additional cost over that model.  For anyone interested in conducting TDS measurements by any method, I would caution them to make sure that the samples are cooled as much as possible before taking readings and to take multiple readings until the number stabilises. I also found the iPhone version of the ExtractMojo software to be convenient, even though the same results could be achieved with a notepad and a calculator.

Apples and Apples

Blind, methodical and systematic sensory evaluation of grinders seems to be an area on which little has been written. Rather than focussing on fine degrees of difference, we put together a lineup of drastically different grinders. Grinder No. 1 is a $3000+, 20-kilogram flat-burred behemoth that can fairly be said to be the industry standard cupping grinder. Grinder No. 2 a $300 small electric conical burr grinder, as well as a similar competitor we’ve called Grinder No. 3. Grinder No. 4 is a $75, ultra-portable hand-cranked ceramic conical burred grinder, rounded out the spectrum.

All grinders were dialled in and evaluated using Market Lane’s Finca La Fany from El Salvador. We chose this coffee because it provides an extraordinarily clean and balanced “classic” cup as opposed to a cup whose attraction is exotic flavour nuances. The taste results given later in this article are relative to the potential of the coffee that we felt was achieved. The grind settings on all grinders were calibrated to deliver a 1.15 per cent TDS cup at a brew ratio of 13.2 grams of coffee to 240 grams of water. For the calibration, coffee was brewed in a clever dripper, which is essentially a filter cone with a valve on the bottom, for 2.5 minutes before releasing the valve. 

The calibration process showed some interesting practical concerns in dialling in the grinders. The venerable Grinder No. 1 has a steel snout through which the coffee exits. Chaff and static sticks to the inside of the snout and the grinder is equipped with a spring-loaded knocker to dislodge this chaff. We found it important to discard the chaff and not to use it. Despite having settings for multiple brew methods on its LCD display grind size readout, the Grinder No. 2 was incapable of grinding coarse enough for our purposes until we opened the grinder and removed a number of spacers below the lower burr. Dialling in Grinder No. 4 was a straightforward process, with the burr separation changed simply by tightening or loosening a nut, but I found myself wishing for a point of reference. By contrast, Grinder No. 3 was quite easy to adjust.

The Results

Samples ground on demand on the four grinders were joined by a fifth sample ground the day before on the top end grinder in a blind tasting lineup. We decided to test the grinders through the traditional “cupping” method, as this allowed for the simultaneous preparation and evaluation of multiple cups of each sample. Given that the grind settings had been calibrated to deliver the same extraction, I secretly wondered if any differences would be discernible, let alone significant. To my surprise, we were presented with five quite distinct cups. 

The pre-ground cup delivered high bitterness and a long, dry and dirty aftertaste. As the coffee sat, the bitterness subsided and the body and mouthfeel were distinctly higher than the other samples, but the overall result was distinctly on first tasting undrinkable and poor after the bitterness had subsided somewhat. Grinder No. 3 delivered an unremarkable and muddy cup, with medium scores across the board; average.

Grinder No. 1 delivered a clean, well-rounded cup with low bitterness, medium-high acidity and sweetness and medium body; excellent. Grinder No. 2 allowed the coffee to express itself in a similar way to Grinder No. 1, but more muted overall, with medium-low scores for body, acidity and sweetness and a short aftertaste. The cups improved significantly in each of these aspects as they sat and continued to brew, though the aftertaste did become slightly chaffy. Overall, the result was good to very good. Grinder No. 4 delivered a good overall result, with a short aftertaste, but the cup was overlaid with a chalky, papery quality.

While I hope that this review sheds light on the subject, the results should certainly not be taken as a comprehensive evaluation of all grinders on the market. Rather, I think that two limited conclusions can be drawn. First, that the difference between the cups produced by different grinders cannot be eliminated by calibrating them to achieve extractions of the same strength. Indeed, the differences in performance between Grinders No. 2 and 3 shows that even grinders of a similar price range and burr type can deliver quite different results in the cup Second, that the advice to avoid pre-ground coffee is probably pretty sound.

Luca Costanzo runs coffeereviewaustralia.com and placed third in this year’s World Brewer’s Cup. Luca would like to thank Market Lane Coffee for the use of its facilities and Jason Scheltus for his help as a guest reviewer.