The Conical or The Flat: Which is Best?

Anyone who has recently shopped for a drip coffee brewer will have noticed that modern brewers usually come with a "semi-conical" or "flat bottom" filter basket. The improved flow through the coffee grounds, the increased extraction uniformity, and the correspondingly improved taste are eloquently represented by fans of semi-conical baskets. Confusingly, fans of flat-bottom baskets would claim almost the same advantages for their chosen method. However, until now there has not been any rigorous science to back up these claims.

In 2017, the University of California Davis Coffee Center was asked by the SCA to conduct research aimed at extending and updating the classic drip brewing control chart. In the process of this research, the researchers decided to discuss the issue of flat-bottom versus semi-conical filter baskets. In all of the experiments the researchers used the Sage Precision Brewer.

Before answering which is method is better however, the question, "Is there even a difference?" must first be answered. Although many coffee lovers may present passionate and convincing arguments, there is always the possibility that there is simply no obvious or statistically significant difference. To start the researchers used "discrimination testing," (or, triangle tests) to assess if there's a disparity. In these experiments, three cups of coffee were presented to a panellist, two of which were similar and one of which was different. The panellist was then required to spot the difference. 

The results to the first experiment were both exciting and counterintuitive! The researchers found that when comparing the shape of the flat vs. cone basket, regardless of whether using a medium or fine grind, the different cup was correctly defined by a statistically significant majority of panellists.

So, for those coffee fans who argue that the geometry of the basket affects the taste, the results of this experiment agree!


On the reverse side, however, the experiments also showed that the difference in grind size could not be identified by the non-expert panellists. So, for coffee lovers who defend the need to make constant precise adjustments to the grind size, it looks like out that the average Joe can not taste the difference, at least as far as drip brew is concerned (and at least over the range of grind size used by the researchers) - Note that for “medium grind” the researchers had a median particle size of 1,065 microns, whereas the “medium-fine grind” had a median particle size of 799 microns, a 25% difference in size.

Now, to address the question of what the difference is, the researchers then performed a series of detailed “sensory descriptive” experiments. For this, they trained (expert) panelists to assess the intensity of various flavor attributes, such as “smoky,” “citrus,” “bitter,” etc, using a total of 26 different flavor attributes, training them on the WCR tasting lexicon with appropriate sensory references

Among other findings, the researchers found that for light roasted coffee baskets that are flat-bottomed produce flavours with more dried fruit, sweet, and floral flavour intensities, while conical baskets produce more citrus, berry, and acid. 

So, which filter is the greatest? 

For now, though, you might want to know: which is the best basket shape? The response, of course, is that "best" is whatever brewing method tastes the best for you, and it is up to each person to decide. At the very least, though, you can use the hard data in this article to shed some light on the debate the next time anyone starts debating the merits of flat-bottom vs. conical filter baskets.

Thanks for reading. We are not sure whether this article has made your buying decision any easier, but we think the take home point is, whatever method you choose, have fun using and enjoying the unique characteristics which it highlights. If you can, why not even experiment with both yourself!


Article adapted from SCANews post. For full article please see the following