#4: Post by MoJo » April 10th, 2011, 12:17 pm

1) Barista Magazine is not a scientific journal, and this is not a scientific article.

2) The reference list included of studies on coffee and cholesterol, not filter baskets. AFAIK the claim that properly designed filter baskets reduce diterpenes by half (p.75, first column, first paragraph) is unsubstantiated by these references. It is certainly not supported by any evidence in this article.

3) The graphs in Fig.3-4 are presented as though they were actual data, when it's obvious that normal distributions have been artificially generated to illustrate a point.

4) Statements about hole area being "unmeasurable" (p.76, second column, last paragraph) are demonstrably incorrect. Hole number and area are readily computed by well-known image processing operations. It's true that average hole diameter may not be meaningful when there is huge variability in hole size and shape, but that's a different claim entirely.

e) The implication that histograms were developed by VST (p.76, second column, first paragraph) is absurd.

f) Statements about basket shape and hole area are presented without supporting evidence. For example, it makes sense that there will be dead spots in the extraction when the holes do not cover the entire bottom of the basket. But it does not follow that slanted basket sides will cause dead spots.

Again, let me emphasize that I regard this as important, pioneering work. My thanks to Vince Fedele for his publication, and to Andy Schecter for bringing it to our attention. I hope it will be followed up by more careful studies that either back up or refute the claims in the article. Such studies may provide a major step forward in both the theory and practice of espresso extraction.

I too remain skeptical of claims that espresso nirvana may be achieved through better filter baskets. But I'm open to any new ideas that are backed by persuasive evidence. For example, if TDS consistency improves with certain filter baskets, I'd be in the market.

Hi John, and thanks for your comments.I don't see where barista MAG claims to represent itself as a scientific journal, nor do I state anywhere in the article that it's intended to be a scientific one. In the limited space available, naturally, some supporting documentation could not be included. Including what you propose would have taken tens of thousands of words, charts, graphs and summary findings, but this article was limited to 3K-5K words, and intended to address the general barista and specialty coffee community.May I suggest you please re-read that section, I believe you mis-read or mis-interpreted it. It does not say that diterpenes are reduced by half, rather, it says that sediment levels can be reduced by about half. From Hilbrich, Daniel A.: The compounds cafestol and kahweol are present in the fine particulate sediment, in the lipid fraction (coffee oils) (both which pass through metallic filtration), and as pointed out by some of the references, have been extensively studied by medical researchers and have been conclusively shown to substantially elevate serum, cholesterol, triglycerides, and liver function tests.That said, using the references provided, you can readily find your own supporting evidence, by following these references to others, including medical references and various patented processes on filters that provide plenty of support for the implied corollary that if the sediment can be reduced to half, then some of the compounds cafestol and kahweol present in the fine particulate sediment are also reduced.From there, the article describes clearly how you can further measure the difference in non-dissolved solids as a fraction of total brew solids using readily available methods. Finally, it states that you can see a significant spike in the measurable particulate component when using a filter that has some significant percentage of its holes that are over-sized versus a targeted average.There are few to no references to filter baskets to quote from. The only other reference I'm aware of is M. Petracco of Illy, who mentions non-dissolved solids are typically 10% as a percentage of TBS (total brew solids = dissolved plus non-dissolved solids), which agrees with what we measured in some typical filters. It was not the intent to provide the entire method and supporting evidence, there simply was not room, but it is easily reproducible, using the method described.Thank you for pointing out that "it's obvious the distributions have been generated to illustrate a point". You are 99% correct, that is exactly what was done, and the intent was for illustrative purposes, as you surmise. The original caption said "Illustration of..." versus "Example of..." but those captions were lost in the original formatting and layout. In the original presentation of materials those graphs were excerpted from an animation that illustrated how [mean] particle size moved as a function of grind setting, and stated exactly that point, unfortunately the word "Example" replaced "Illustration" in the caption. That said, it was obvious to you, and so I hope it's obvious to other readers as well, thank you for pointing it out. The graphs were not, however, artificially created, they were normalized from actual distribution data of particle and hole size distributions, emphasizing the mean. Another point from the illustration statement that was left out of the article was that the particle size [normalized] distribution ignored the smaller bi-modal component, usually around 20-80µm in size, showing the majority components usually ranging 200-800µm in size. That said, I hope you understood the intended point of the "illustration", as it provides important background as to why you can measure some filters that produce 4-5% non-dissolved fraction of total brew solids (sediment) while other filters produce 9-12% non-dissolved fraction of TBS, whose shots can taste vegetal, and provide an unpleasant, chalky mouth feel, and contain approximately double the amount of [undesirable] sediment. It was also meant to illustrate why in some filters, users frequently have a great deal of difficulty pulling shots consistently when particle size is smaller than or significantly overlaps the mean hole size distribution, and grind settings seem extremely sensitive.Not sure what your objection is, John. VST didn't make that statement, the metrology lab made the statement, because the apparatus to make the measurement was not known or was otherwise unavailable to perform the required task. Calls to a number of other metrology labs in the U.S. resulted in similar dead ends.The "demonstrably incorrect" comment, I assume means that it was demonstrated that certain image processing operations could be performed, was true only after VST developed a system and methodology to do so, and to come up with meaningful ways to actually use the data as applied specifically to espresso filters. If that pre-existied, no one I could find was aware of it either inside of the filter manufacturing industry or outside, where one would normally look to find it. Your comment seems to imply that the process as applied to espresso filters has been in wide spread practice for years, but to the best of my knowledge, that is not the case, or if it has been done, no one has published it or otherwise made such a system available.Finally, we agree, it's true that average hole area (diameter is only valid if the hole is circular) may not be meaningful if there is huge variability in hole size and shape, but that's a different claim entirely - was exactly the point of applying a histogram analysis as part of the evaluation methodology.I agree, you're right, that is absurd, but once again, I never stated VST developed the histogram on pg 76, nor elsewhere. Nor was it meant to be implied, sorry you read it that way. As Dave Walsh says, "Read, absorb, read again". That said, I'm unaware of anyone else who has ever used the tool to evaluate espresso filters. What was stated was that the histogram was one of the tools applied to the evaluation process. The histogram, combined with other measurement data became part of a grading method that allows a single number to describe several important attributes of the quality factor of a filter, the topic of an upcoming article.Fair criticism, John. Again, there was not room in the space allowed to provide all of the data, and some data were left out intentionally. The article simply stated our observations that significant shot-to-shot variations could be measured from such filters, which anyone can easily repeat using commonly available measurement tools. Similarly, the same measurements made using several different but uniformly fabricated filters with an open area under the entire coffee puck yielded far less shot-to-shot variances.Appreciate the kind words, John. While I'm sure this response will do little to satisfy your scientific appetite, I appreciate your comments and perspective, and hope you understand there was neither the space nor was it the intent to provide a "scientific article" about the subject matter. Rather, it was intended to address a problem that has plagued the industry for decades, and how some steps have been taken towards addressing those problems. Accessibility was another goal, and the style of presenting the findings was to appeal to the general barista community versus a strictly scientific paper.No one said nor claimed "espresso nirvana", but I like that phrase. What I hope did come out of the article was that maintaining specific design parameters and manufacturing with precision could produce filters that performed not only identically to each other, but also extracted into a desired area of the brewing control chart predictably, and would do so consistently over time, thus eliminating a host of problems that have been troublesome for the industry for the past many decades. Kind regards—Vince