Recent Studies on Coffee: Part 2 - Semi-Conical vs. Flat Bottom Brewers

Here’s part two in our mini series exploring some of the recent scientific studies done on coffee. This time, we’re looking at The Effect of Basket Geometry on the Sensory Quality and Consumer Acceptance of Drip Brewed Coffee. Rather than simply comparing different basket geometries, they compared different basket geometries with different roast level coffees as well as at different grind sizes. Here’s the full study: https://pages.uoregon.edu/chendon/coffee_literature/2019%20J.%20Food%20Sci.,%20%20Basket%20geometry%20from%20sensory%20--%20no%20control%20for%20concentration.pdf

Basically, the results are that consumers notice a difference in flavor and have a preference between semi-conical and flat-bottomed brewers, but the difference and preference is not nearly as significant as the differences in flavor and preferences generated by different roast levels and grind sizes.

However, there are some major issues to address…

Figure 1 is massively concerning to us - the distance between showerhead and coffee grounds with the flat bottom basket is 7cm but the distance between showerhead and grounds with the semi-conical is only 4cm, so the same flow rate from the showerhead is giving massively different agitation to the slurry. The amount of agitation plays a huge role in how much extraction a given brew has. We understand of course that if you use the same dose with both baskets, if you are just looking at swapping baskets on a given brewer that this difference is going to be a thing, but it means that the experimental results are NOT just comparing basket shapes x roast or x grind, they are comparing (basket shape + agitation) x roast or x grind, which is a totally different thing. If one were to replicate this experiment, but by pouring with a kettle from a constant height above the slurry (a simple way to do this with excellent consistency would have been to use a modbar pourover system and adjust the height of the spray head so that the height above slurry is a constant), you might get entirely different results.

Another potential issue with this study is the tasting temperature - it seems too high. 65 C is 149 F. It's much easier to taste coffee at more like 120-130 F.

One massive thing, which they do mention, but we feel needs to be stressed, is that a significant portion of the difference in perceived flavor is due to differences in strength rather than extraction yield. There have been studies published on this effect in the past, and it would have been quite easy to dilute the stronger brews down to the same TDS as the weaker brews so that the tasters could have identified solely the differences in extraction, rather than extraction and strength at the same time.

Finally, 50% of the tasters normally put some type of sweetener or milk/cream/etc into their coffee. Why are these studies not done with people who only drink black coffee? The tasting in this experiment was all done with just black coffee. These tasters, when actually brewing at home, will put something in their coffee. So this is not representative of what consumers will do at all. It is not relevant in any way whatsoever if a person who normally puts milk in their coffee says that they prefer the darker roast flat bottom basket brew (black) over the darker roast semi-conical basket brew (black) (or whatever example you want to pick) as they will never be choosing between those things as a consumer.

They should have had the people who normally put something in their coffee put that something in their coffee for this experiment (which of course would pretty significantly change the experiment), or excluded them from the experiment entirely. This may be less of an issue than it initially seems, as the most liked coffees were the ones described as sweet, berries, etc and least liked were burnt, smoke, ash, etc.

In conclusion, we don’t really think there’s much of any conclusion that you can or should draw from this experiment, apart from the obvious fact that some consumers prefer lighter roasts over darker (and vice versa). We certainly do not recommend picking a flat bottom (or a semi-conical) basket brewer based on the results presented in this study.