Editor’s Note: This article first appeared in Daily Coffee News on October 10, 2018; it is reprinted here with permission.
Following a dizzying week of coffee science learning in mid-September at the Association for Science and Information on Coffee (ASIC) biennial symposium in Portland, Oregon, I attempted to sum up of some of the conference’s many day-one highlights.
That piece explores a range of issues, including caffeine metabolism, biomarkers in coffee, fermentation biology, climate issues, the economics of cooperative farming, soil science and more.
Today we dive even deeper, exploring some of the conference’s major takeaways regarding roasting and brewing science, and plant science and pathology.
Degassing of Roasted Coffee
The second day’s opening keynote was presented by Dr. Samo Smrke of the Zurich University of Applied Sciences. His research included extensive work on degassing of roasted coffee, quantifying some data that I suspect many roasters already know, at least anecdotally.
Dark roasted coffee degasses more than light, fast roasts degas more and more quickly, and even after long term whole bean storage, a small amount of CO2 is still accessible once the coffee is ground. Smrke found that aged coffee has a faster flow rate as espresso than fresh roasted, and that high temperature storage environments have a massive impact on freshness. In an extreme example, 70 days of resting at -25C (-13F) was roughly equivalent to two days at 35C (95F). Interestingly enough, oxygen was not observed as a significant staling factor at temperatures below 15C (59F).
Brewing and Roasting Science
Some interesting research in general brewing and roasting science was reported by various parties during the course of the symposium, and here are some highlights:
- André Eiermann, the 2017 Swiss Barista Champion, presented some research indicating that factors like higher dose, finer grind, and darker roast can increase the TDS of a capsule-brewed coffee, and that higher extraction time might correlate to lower acidity ratings. Some of his findings contradict some old, more informal data analysis I performed relating extraction and roast level.
- Claudia Passos hypothesized that spent carbohydrates from coffee brewing could be used as a delivery mechanism for medication taken by an inhaler.
- Scott Frost from UC Davis suggested that the pulsing cycle of a coffee brewer can have a dramatic effect on extraction, where shorter, more frequent cycles increase extraction.
- Dr. Jean Xavier Guidard of UC Davis noted higher TDS and more consistent results from conical shaped brewers as compared to flat bottom baskets, and that basket shape is more important than small grind adjustments in extraction.
- Mackenzie Batali of UC Davis offered insights on extraction data, noting that 50 percent of coffee is extracted within the first 200mL of brewing. A doctoral candidate, Ms. Batali mentioned she’d referenced Sandra Elisa Loofbourow’s similar analysis for Royal in her research!
- Keiko Iwasa from Suntory was able to trace some important contributors to coffee flavor, particularly fresh fruity aromas, to esters formed in roasting, themselves a result of Methanol, also formed during roasting, indicating that many of the flavor compounds we appreciate are not present at all in green coffee, but must be drawn out in the roast.
- Ralf Zimmermann of Probat demonstrated that light roasts contained the highest amounts of antioxidants in his study.
- Samuel Lopane of Clemson University was able to demonstrate that the shelf life of cold brew need not be limited by microbial activity — of which none was detected — but rather should be determined by sensory changes. He also noted that the rise in popularity of cold brew is almost certainly linked to the ability for consumers to take home specialty coffee without having to worry about how to brew it.
Sequencing the Arabica Genome
Thursday’s lectures were among the most difficult for me to keep pace with. Dr. Alexandre de Kochko of the Institute of Research for Development, Marseille, presented information related to the sequencing of the Arabica genome, a very recent accomplishment with a number of difficulties overcome in its execution. Sixty-four researchers were involved in the project, which was able to confirm Arabica’s spontaneous origin from parent species Canephora and Eugenioides. This lineage made sequencing difficult, de Kochko explained, because the parent genetic material is very similar. Arabica is composed of more than 60 percent transposable elements, and 88 percent of its genes are expressed by both parents.
Dr. M. Catherine Aime of Purdue University presented a technical but highly engaging lecture on the rust fungus. There was a lot to take in, and much of it bears repeating, so I’ll do my best to be both accurate and succinct in my summary. Rust fungi encompass around 8,000 species — roughly the same as the number of bird species in the world — and account for around 8 percent of described fungi to date. While most other fungi are primarily engaged in decomposing already dead material, rust are “obligate biotrophs,” meaning they need a living host to survive. Rust also represents one of nature’s most complex life-cycles, engaging in up to five stages using both sexual and asexual forms of reproduction and requiring two separate species to host.
Rust is an ancient organism. The coffee leaf rust genus is thought to be one of the first rust strains to evolve, around 140 million years ago, roughly coinciding with the emergence of the first flowering plants. Human interaction in history shows numerous instance of epidemics:
- The “red barley sickness” noted in Mesopotamia some 1500 years BCE
- During the Roman era, a rust god was created, “Robigalia”
- Some theories link the fall of the Roman Empire to a wheat shortage due to a rust epidemic
- In 1660 France enacted a ban on the barberry plant, noting its presence linked with wheat rust, but it wouldn’t be until the 1950s that barberry was identified as the alternate host of the wheat rust fungus.
- In 1918 a wheat rust outbreak in the US South resulted in wholesale replacement of the crop and the rise of classic Southern culinary curiosities like grits (substitute for cream of wheat) and bourbon (corn whiskey as a substitute for barley).
- In the 21st century, science has observed a rapid increase in globally important rust outbreaks, likely related to two factors: increased human mobility and climate change.
With regard to coffee, the coffee leaf rust (CLR) species, Hemileia vastatrix, has not yet been observed in two of the five life stages, and thus the alternate host has not yet been identified. There’s speculation that CLR first evolved on a different species in the Rubiaceae family, and didn’t migrate to coffee until the production boom in the 1800s. This is based on the fact that other Rubiaceae plants can act as hosts, but generally aren’t killed and won’t result in epidemics, indicating an evolutionary resistance that is lacking in coffee.
CLR was first observed in 1861 in Lake Victoria and by 1867 it was noticed in Ceylon. First formally described by Reverend H. J. Berkele & Mr. Broome on Ceylon in 1869, the ensuing epidemic would ravage Arabica plantations throughout the Indian and Pacific oceans, but it wasn’t first observed in the continental Americas until much later, as late as 1970 in Brazil.
More Plant Science and Pathology
Some further highlights from the fields of plant science and pathology include these notes I hastily scribbled down on Thursday follow below:
- Jean-Christoph Breitler of CIRAD looked into simple, efficient, and inexpensive gene editing techniques used to adapt Robusta to climate change, reducing susceptibility to rancidity, and reducing caffeine. He stated that a non-GMO plant could be obtained at the first subsequent generation after gene editing.
- Solene Pruvot-Woehl of World Coffee Research presented an analysis of submitted coffee plant samples from various producers seeking to verify their cultivars. Two big takeaways: only about 38 percent of the submitted Gesha samples were a true match to the CATIE reference sample, and the Bourbon/Typica group is far wider than just two varieties, likely related to the historical variety dissemination from places like Yemen and India.
- Bernard Gichimu of the University of Embu noted a wide variation in Robusta markers in Ruiru 11, ranging anywhere between 8.7 percent to 24.14 percent, yet could not find a statistical correlation to cup quality.
- Dominique Crouzillat of Nestlé examined the strong geographical coincidence with genetic distinction in the major Robusta groups found in Africa, noting wide diversity in the species.
- Sarada Krishnan of the Denver Botanic Gardens and World Coffee Research illuminated the need for better preservation of coffee seed banks. Most collections date back to the 1960s with risk of loss, cross-pollination, lack of funding, and unsuitable environments, in their survey. They identified four origin collections in which to prioritize investment: CATIE (Costa Rica), CNRA (Côte d’Ivoire), EBI (Ethiopia) and FOFIFA (Madagascar). An immediate complaint was logged by a researcher at JARC (Ethiopia), as this collection is generally seen as a critical one in the development of varieties used throughout Ethiopia.
- Eric Rahn of CIAT offered insights into coffee flowering, and how this might be the “bottleneck” in coffee’s ability to adapt to climate change. While plants can grow in higher temperatures, and do indeed enjoy the increased CO2 resources, their ability to reproduce — to flower and produce fruit — will be limited. He noted that the reproductive success threshold for coffee is typically cited at 30C (86F) and that future climate predictions put 1800 masl in Cauca, Colombia, for example at 30C+ consistently by 2032 — a date that is terrifyingly close.
- Juan Carlos Herrera of CENICAFE presented research on tree stress levels and susceptibility to leaf rust. Under stressful conditions — too much light, not enough Nitrogen in the soil — all plants studied were more prone to infection, but the pure Arabica Caturra cultivar was at far higher risk to leaf rust under stress compared to hybrid Catimor types.
- Valerie Poncet of Universidade Federal de Lavras raised awareness about the risk of Ugandan Robusta to climate change, predicting 2.7x decreased rate of habitability by 2050, noting that some geographical locations like Zoka were at higher risk than others like Budongo.
- Christophe Montagnon of World Coffee Research presented research on the sensory impact of the compound limonene, and how the presence of this single chemical, present in the peel of citrus fruits, could be the difference between the highest sensory quality coffees and those that qualify as specialty but not “top” specialty. His comments were met with some skepticism by the room, as much sensory science has focused on the absence of negative characteristics vs. the presence of positive ones.
- Stephanie Alcala, an employee of Coffee Manufactory and a doctoral candidate at the University of Michigan, presented her research on genetic variations within the Gesha population the famous Hacienda La Esmeralda. By physical appearance, the trees were grouped into three phenotypes: typical, atypical, and dwarf. Gene sequencing concluded that the trees have some “plasticity” in their appearance not related to genetics, that the dwarf plants showed some proximity to Catuai — also a dwarf plant — but that generally the genetic sequencing was not conclusively correlated to physical appearance.
- Dora Batista of IICT highlighted a number of interesting characteristics of the leaf rust fungus, and I noted with interest her speculation that the proximity of different coffee species (Arabica and Robusta, for example) could potentially enhance the severity of the affliction.
All told, after four very full days, I had a lot to digest, and I suspect that if the lively conversations over coffee and dinners were any indication, so too did the scientists.
There’s much to look forward to in advances related to coffee, and as the future presents challenges, I look forward to seeing and participating in evidence-based solutions. Onward!