Tag: Nanotech

Scientists from Karlsruhe Institute of Technology (KIT) and the Indian Institute of Technology Guwahati (IITG) have developed a surface material that repels water droplets almost completely. Using an entirely innovative process, they changed metal-organic frameworks (MOFs)—artificially designed materials with novel properties—by grafting hydrocarbon chains.

The resulting superhydrophobic (extremely water-repellent) properties are interesting for use as self-cleaning surfaces that need to be robust against environmental influences, such as on automobiles or in architecture. The study was published in the journal Materials Horizons.

MOFs (metal-organic frameworks) are composed of metals and organic linkers that form a network with empty pores resembling a sponge. Their volumetric properties—unfolding two grams of this material would yield the area of a football pitch—make them an interesting material in applications such as gas storage, carbon dioxide separation, or novel medical technologies.

The outer surfaces exposed by these crystalline materials also offer unique characteristics, which the research team took advantage of by grafting hydrocarbon chains onto thin MOF films. They observed a water contact angle of more than 160 degrees—the larger the angle formed by the surface of a water drop with the substrate, the better the hydrophobic properties of the material.

“With our method, we are able to achieve superhydrophobic surfaces with contact angles that are significantly higher than those of other smooth surfaces and coatings,” states Professor Christof Wöll from KIT’s Institute of Functional Interfaces. “Although the wetting properties of MOF powder particles have been explored before, the use of monolithic MOF thin films for this purpose is a groundbreaking concept.”

Next-generation ‘superhydrophobic’ materials

The team attributes these results to the brush-like arrangement (polymer brushes) of the hydrocarbon chains on the MOFs. After being grafted to the MOF materials, they tend to form “coils”—a state of disorder that scientists call “high-entropy state,” which is essential for its hydrophobic properties. The scientists asserted that this state of the grafted hydrocarbon chains could not be observed on other materials.

It is remarkable that the water contact angle did not increase even when they used perfluorinated hydrocarbon chains for grafting, i.e., substituting hydrogen atoms with fluorine. In materials such as Teflon, perfluorination brings about superhydrophobic properties. In the newly developed material, however, it decreased the water contact angle significantly, as the team found out.

Further analyses in computer simulations confirmed that the perfluorinated molecules—in contrast to hydrocarbon chains—could not assume the energetically favorable high-entropy state.

In addition, the scientists varied the surface roughness of their SAM@SURMOF systems in the nanometer range, thereby further reducing the water adhesion strength. Even with extremely small inclination angles, water droplets started rolling off, and their hydrophobic and self-cleaning properties were significantly improved.

“Our work also includes a detailed theoretical analysis, which links the unexpected behavior shown in experiments to the high-entropy state of the molecules grafted to the MOF films,” says Professor Uttam Manna from IITG’s Chemistry department. “This study will change the design and production of next-generation materials with optimum hydrophobic properties.”

The development of molecules to study and treat disease is becoming increasingly burdened by the time and specificity required to analyze the vast amounts of data generated by synthesizing large collections of new molecules. Scientists at St. Jude Children’s Research Hospital present a novel solution to this problem, using the fundamental fragmentation patterns of chemical building blocks to barcode reactions from starting materials to products.

In doing so, they have removed a key bottleneck in the process of synthesizing and screening small molecules. Their work is published in Nature.

Current analytical methods lag the scale of rapid, high-throughput analysis desired by researchers. Scientists at St. Jude, led by Daniel Blair, Ph.D., St. Jude Department of Chemical Biology and Therapeutics, set about solving this problem by capitalizing on a general feature residing in most chemical reactions.

“Generality is essential for doing anything quickly. So, we sought to identify general features which would uniformly encode the analysis of small molecules,” explained Blair, corresponding author of the article.

“We discovered that the building blocks we use to create small molecules break apart in specific, predictable ways and that these patterns can then be used as universal barcodes to analyze chemical products.”

A fragmentation-first approach to experimental design

Fragmentation is a fundamental property of chemical matter, but this novel application in the realm of chemical synthesis is giving it new meaning. A general rate for analyzing a chemical reaction’s outcome is conventionally around 3 minutes, but as researchers scale up, analyzing additional reactions with more variables, that amount of time becomes impractical.

This work by Blair and the team transforms chemical reaction analysis from a slow, highly customized and specialist-driven method to a streamlined approach driven by simple-to-identify fragmentation barcodes and a single analytical readout.

“Because these fragmentation patterns are a fundamental property of chemical matter, they are reliably transposable from starting materials to products. As soon as you recognize that starting materials can define the analysis of the resulting chemical products, you’ve generalized the entire approach,” said first author Maowei Hu, Ph.D., St. Jude Department of Chemical Biology and Therapeutics.

This fragmentation-first approach to high-throughput experimental design can be applied in many ways because this fundamental property is not disease- or discipline-specific. Future applications may include the development of antibiotics, antifungals, cancer therapeutics, molecular glues and many more types of molecules.

“We’ve not only transformed the speed of chemical reaction analysis but also paved the way for directly utilizing these molecules to understand and combat diseases,” said Blair.

“This advance represents a significant milestone in our mission to develop effective therapies swiftly and efficiently. We’ve transformed chemical reaction analysis from minutes to milliseconds, and in doing so, have shifted the bottleneck from making molecules to finding functions.”

How can aromatic compounds be separated from aliphatic compounds efficiently without having to rely on energy-intensive processes? In an article published in the journal Angewandte Chemie International Edition, chemists from Heinrich Heine University Düsseldorf (HHU) present an innovative molecular sieve made of partially fluorinated macrocycles that can separate these compounds selectively.

Aromatic compounds—substances with flat, ring-shaped structures made up of carbon atoms—play an important role in organic chemistry. Among other things, they serve as solvents or feedstock for many plastics and are also used in fuels. One well-known example is benzene (C₆H₆).

Its aliphatic counterparts, such as cyclohexane (C₆H₁₂), are also ring-shaped. However, by contrast with aromatics, they are flexible and thus form a zigzag-like, three-dimensional structure.

Separating aromatics from other organic compounds—in particular aliphatic hydrocarbons—is a major challenge, yet often necessary. For example, cyclohexane is produced by hydrogenation of benzene, resulting in a mixture of both substances.

Separation processes used to date require a significant amount of energy, as the physical properties of the compounds, such as boiling points and vapor pressure, are virtually identical.

The research team headed by HHU chemist Dr. Bernd M. Schmidt (Functional Supramolecular Systems Research Group) and the research group headed by Professor Dr. Christoph Janiak (Chair for Nanoporous and Nanoscale Materials) have together developed a supramolecular sorting machine, which can realize the separation in a different way. It comprises electron-deficient, fluorinated macrocycles with a rectangular structure called squareimines, which predominantly adsorb aromatic molecules.

Schmidt says, “In the squareimines, small, three-dimensional molecules accumulate in the solid body in such a way that the connection of the cavities creates a network of pores.” This ultimately results in a network of many tubes arranged in parallel next to each other, each of which has a diameter of less than one nanometer. “This porous structure, acting as a ‘supramolecular sponge,’ can trap small molecules such as gases or volatile organic compounds,” Schmidt continues.

The researchers optimized the adsorption capability of their material through the targeted, controlled linking of the structures. Tobias Pausch, Ph.D. student in the research group headed by Dr. Schmidt and lead author of the study, states, “The squareimine NDI2F42 has a strong affinity for aromatic compounds such as benzene and toluene, while ignoring their aliphatic counterparts.”

The chemists are already measuring high selectivities of up to 97:3 for benzene over cyclohexane and 93:7 for toluene over methylcyclohexane in initial tests. “This means that almost exclusively aromatic compounds are adsorbed into the crystalline, supramolecular sponge, while the aliphatic compounds are left behind,” says Pausch.

Schmidt claims, “The identified squareimines offer great potential for molecular separation. This is due not only to their favorable structure, but also to their diversity, making it possible to produce tailored sorters for highly specific compounds. They are also easy to produce, making them a promising platform for new, innovative and lightweight adsorber materials.”

Microbial organisms adapted to extreme and inhospitable environments carry proteins within their proteome that significantly accelerate the dissolution of CO₂ in water, while also withstanding very high temperatures and pH. These enzymes are valuable promoters of CO₂ capturing from industrial exhaust streams. Researchers at the Biomedical Sciences Research Center Alexander Fleming (BSRC Fleming) in Vari, Greece, have identified such a bioactive molecule.

Microorganisms producing resilient proteins and enzymes have evolved to thrive in extreme conditions, such as hot springs, salt lakes, and volcanoes. A team of Greek researchers, led by Dr. Georgios Skretas at BSRC Fleming developed new metagenomic analysis tools to identify a super heat-resistant enzyme of biotechnological interest.

After scanning millions of genes from open-access metagenomic databases, a new promising candidate biocatalyst was found in a metagenomic sample originally collected from a hot spring in the Kirishima region of Japan. Through this process, the scientists from the Skretas Lab discovered the highly stable carbonic anhydrase CA-KR1. This robust enzyme specializes in enhancing the dissolution of CO₂ in water and exhibits unprecedented stability under industrial conditions.

“Metagenomic analysis gives us access to a ‘pool of proteins’ that remains largely unexplored and can unravel enzymes and other proteins of great biotechnological interest, such as the CA-KR1 enzyme we have discovered,” comments Dr. Skretas. According to Dr. Skretas, the CA-KR1 enzyme is extremely stable at very high temperatures and in strong alkaline solutions, which is extremely rare for proteins.

“More specifically, the enzyme performs exceptionally well under conditions of Hot Potassium Carbonate (HPC) capture technologies, with temperatures exceeding 80 °C and pH levels above 11. It enhances CO₂ capture productivity by 90% at 90 °C compared to standard non-enzymatic methods. It also allows for 90% CO₂ removal at 80 °C, surpassing the performance of standard HPC capture and doubling the initial CO₂ absorption rate at 90 °C,” explains Ph.D. candidate Konstantinos Rigkos, who, along with the Post-Doctoral Researcher Dimitra Zarafeta, played a central role in this study, recently published in Environmental Science & Technology.

“The CA-KR1 enzyme is perhaps the most robust biocatalyst (carbonic anhydrase) for efficient CO₂ capture in HPC conditions reported to date. Its integration in industrial settings holds great promise for accelerating the industrial implementation of biomimetic CO₂ capture—a green, sustainable technology expected to be a ‘game changer’ in carbon sequestration, significantly contributing to the timely achievement of carbon neutrality,” added Dr. Zarafeta.

The innovative enzyme CA-KR1 is already patent-pending. Its transition from the laboratory bench to the industrial bioreactor will be an important step toward industrial decarbonization, significantly contributing to innovation in the critical area of CO₂ capture for the well-being of the planet. These studies are currently underway.

Nitrogen oxides (NO_x) are a group of gases formed by nitric oxide and nitrogen dioxide. They are produced, above all, by the burning of fossil fuels. Due to their harmful effects on human health and the environment, in recent years they have been in the scientific community’s crosshairs.

A research team at the Chemical Institute for Energy and the Environment (IQUEMA), attached to the University of Cordoba, has developed a photocatalytic material capable of effectively reducing these gases, achieving results similar to others developed to date, but through a more economical and sustainable process. The findings are published in the journal Advanced Sustainable Systems.

There are chemical reactions that can be favored or accelerated in the presence of light. In the case of nitrogen oxides, light energy, in the presence of a material that functions as a catalyst, makes it possible to oxidize the nitrogen oxides in the atmosphere and convert them into nitrates and nitrites.

The first author of this research paper, Laura Marín, explained that, unlike other photocatalytic reactions, which only operate under ultraviolet light, this new material boasts the advantage of working effectively with visible light, which is much more abundant and makes up most of the solar spectrum, allowing greater use to be made of the sun’s energy.

To do this, the research team has synthesized a new compound by combining two different types of materials: carbon nitride (which allows the reaction to be activated in the presence of visible light) and lamellar double hydroxides, which have the capacity to catalyze the reaction, in addition to featuring economical and easily scalable production.

Professor Ivana Pavlovic, one of the researchers who participated in the study, explained that the new process is capable of converting 65% of nitrogen oxides under visible light irradiation, a percentage very similar to that achieved by other photocatalysts, but with the advantage that this new system uses minerals such as magnesium and aluminum, which are “cheaper, abundant in nature, and benign, compared to other photocatalysts used to date, which contain cadmium, lead or graphene,” the researcher pointed out.

Professor of Inorganic Chemistry and IQUEMA Director Luis Sánchez explained that, in this way, the work represents an important step towards the large-scale development of a system that makes it possible to decontaminate the air under real-world conditions, thus reducing one of the most common pollutant gases in cities, and one whose long-term effects can cause serious health problems.

Currently, most vitamins are produced in factories, either synthetically or with the help of microorganisms that are not approved for food use. These production methods require extensive and often complex purification processes (to separate the vitamin from non-food-approved materials), which are costly and energy-intensive.

Now, a team of researchers from the Technical University of Denmark (DTU) has successfully produced vitamin B2, also known as riboflavin, in significant quantities using a novel, cost-effective, and climate-friendly method.

The researchers employed a food-approved lactic acid bacterium, demonstrating that it can produce vitamin B2 when subjected to heat. The study is published in the Journal of Agricultural and Food Chemistry.

“I think it’s beautiful that something as simple as gentle heating and lactic acid bacteria can be used to produce vitamin B2. The method allows for food to be fortified with vitamin B2 in an easy way, for example, during the production of yogurt or sourdough,” says Associate Professor Christian Solem from DTU National Food Institute, who led the research.

Vitamin B2 is essential for energy production and for maintaining a normal immune function. It also plays an important role in iron absorption, and deficiency has wide-ranging effects.

Fortification with B2 as part of food preparation

This innovative method integrates vitamin production into the food fermentation process. Vitamins can thus be produced and added locally. By using riboflavin-producing bacteria in food production, manufacturers can improve the nutritional value of traditional foods economically, enhancing public health while reducing environmental impact.

The method differs from existing technologies by being natural—without genetic modification—and consuming less energy and fewer chemicals compared to traditional synthetic vitamin production. Fortification only requires basic fermentation tools, which are already common in many households.

How the researchers stressed the bacteria

The team subjected lactic acid bacteria to “oxidative stress,” a natural pressure that compels bacteria to produce more riboflavin to protect themselves.

“We used the microorganism Lactococcus lactis, commonly known from cheese and cultured milk, to produce vitamin B2. Lactococcus thrives best at around 30°C, but we heated the bacteria to 38–39°C, which they didn’t like. Bacteria adapt to new conditions, and to defend themselves against the oxidative stress caused by the heat, they started producing vitamin B2,” explains Solem.

The researchers optimized the vitamin production process by adding various nutrients, achieving a production of 65 milligrams of vitamin B2 per liter of fermented substrate—nearly 60 times the daily human requirement for the vitamin.

Cultural compatibility and future potential

“It would be ideal to package these B2-producing lactic acid bacteria as a starter culture that can be added to foods like milk, maize, or cassava for fermentation. When these foods are fermented using the starter culture, which includes specially selected lactic acid bacteria along with traditional ones, they automatically produce riboflavin while maintaining the traditional flavor and texture of the food,” says Christian Solem.

Many developing countries already have strong traditions of fermenting foods, which extends shelf life and reduces waste.

The method could potentially be expanded to produce other essential vitamins and nutrients, such as folic acid (B9) and vitamin B12, which are often lacking in plant-based diets. It could also be applied to various food types, including sauerkraut.

DNA stores the instructions for life and, along with enzymes and other molecules, computes everything from hair color to risk of developing diseases. Harnessing that prowess and immense storage capacity could lead to DNA-based computers that are faster and smaller than today’s silicon-based versions.

As a step toward that goal, researchers report in ACS Central Science a fast, sequential DNA computing method that is also rewritable—just like current computers.

“DNA computing as a liquid computing paradigm has unique application scenarios and offers the potential for massive data storage and processing of digital files stored in DNA,” says Fei Wang, a co-author of the study.

In living organisms, DNA expression occurs sequentially: Genes are transcribed into RNA, which is translated into proteins. This process happens to many genes simultaneously and repeatedly. If researchers can duplicate this complex, elegant dance in DNA-based computers, these devices could be more powerful than current silicon-based machines.

Researchers have demonstrated sequential DNA computing for very focused, specialized tasks. But until recently, not much progress had been made in developing more general and programmable DNA devices that could be used and reused for various applications.

In previous research, Chunhai Fan, Wang and colleagues developed a programmable DNA integrated circuit with many logic gates that act as instructions for the circuit’s operations. Here’s how it worked:

• Data, 0 or 1, was represented by a short piece of single-stranded DNA, called an oligonucleotide, that contained a series of bases: adenine, thymine, guanine and cytosine. (In nature, the sequence of bases codes for a gene.)
• For example, two inputs of 1 (DNA strands 1 and 2) would interact with an OR logic gate DNA molecule.
• Then in a fluid-filled tube, the input oligonucleotide interacted with a logic gate DNA molecule and generated an output oligonucleotide.
• The output oligonucleotide bound to a different single-stranded DNA that was folded into an origami-like structure, called a register in computer lingo.
• The oligonucleotide was “read” by reviewing its base sequence, released and used in a vial containing the next gate, and so on.

This process took hours, and someone had to manually transfer the oligonucleotide from one gate to another vial for the next computing operation. So the team, along with Hui Lv and Sisi Jia, wanted to speed things up.

To make the reaction processes more efficient and compact, the team first placed the DNA origami register onto a solid glass 2D surface. The output oligonucleotide floating in liquid from a specific logic gate then attached to the glass-mounted register.

After the output oligonucleotide was read and the logic gate instructions determined, it detached, which reset the register so it could be rewritten, thereby avoiding the need to move or replace registers.

The researchers also designed an amplifier that boosted the output signal so all the pieces—the gates, oligonucleotides and registers—could find one another more easily. In a proof-of-concept experiment, all the DNA computing reactions took place in a single tube within 90 minutes.

“This research paves the way for developing large-scale DNA computing circuits with high speed and lays the foundation for visual debugging and automated execution of DNA molecular algorithms,” says Wang.

Street art takes many forms, and the vibrant murals on the Berlin Wall both before and after its fall are expressions of people’s opinions. But there was often secrecy around the processes for creating the paintings, which makes them hard to preserve. Now, researchers reporting in the Journal of the American Chemical Society have uncovered information about this historic site from paint chips by combining a handheld detector and artificial intelligence (AI) data analysis.

“The research highlights the powerful impact of the synergy between chemistry and deep learning in quantifying matter, exemplified in this case by pigments that make street art so captivating,” says Francesco Armetta, a co-author of the study.

To restore or conserve art, it’s important to collect information on the materials and application techniques. But the painters of the Berlin Wall didn’t document this. In previous studies of other historic artifacts, scientists brought fragments or even whole objects into the lab and, without destroying the samples, identified pigments on them using a technique known as Raman spectroscopy. Although handheld Raman devices are available for on-site investigations, they lack the precision of full-sized laboratory equipment.

So, Armetta, Rosina Celeste Ponterio and colleagues wanted to develop an AI algorithm that could analyze the output of portable Raman devices to more accurately identify pigments and dyes. In an initial test of the new approach, they analyzed 15 paint chips from the Berlin Wall.

The researchers first magnified the chips and observed that they all had two or three layers of paint with visible brush strokes. The third layer in contact with the masonry appeared white, which they suggest is from a base coat used to prepare the wall for painting.

Next, the researchers used a handheld Raman spectrometer to analyze the chips and compared them to spectra collected from a commercial pigment spectra library. They identified the primary pigments in the samples as: azopigments (yellow- and red-colored chips), phthalocyanins (blue and green chips), lead chromate (green chips) and titanium white (white chips). These results were confirmed with other non-destructive techniques, including X-ray fluorescence and optical fiber reflectance spectroscopy.

Then, the researchers mixed pigments from a commercial acrylic paint brand (used in Germany since the 1800s) with different ratios of titanium white, trying to match colors and the range of tints typical for painters. A knowledge of these ratios could help art conservators prepare the right materials for restoration, say the researchers.

Using the mixtures’ handheld Raman spectral data, they trained a machine learning algorithm to determine the percentage of pigment. The approach indicated that the Berlin Wall paint chips contained titanium white and up to 75% of pigment, depending on the piece analyzed and according with the color tone. The researchers say these results indicate that their AI model could provide high-quality information for art conservation, forensics and materials science in settings where it’s hard to bring lab equipment to a site.

Trillions of bacteria work in the chemical and pharmaceutical industries, helping produce everything from beer and facial creams to biodiesel and fertilizer. The pharmaceutical industry, in particular, relies heavily on bacteria for producing substances like insulin and penicillin.

Harnessing bacteria’s industrial contributions has revolutionized global health, but their work comes at a high energy cost. Additionally, solvents and continuous production of new bacteria are often necessary, as they don’t last long in their jobs.

Changzhu Wu, a chemist and associate professor at the Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, is focused on making industrial bacteria more robust and useful. His goal is to reduce the energy, time, and unwanted chemicals required to maintain bacteria, while also making them reusable so they can work longer before needing to be replaced.

His latest innovation introduces a type of “super-powered” bacterium and is published in Nature Catalysis.

“We took a common industrial bacterium, E. coli, and essentially gave it a ‘Superman cape’ to enhance its catalysis capabilities. This reduces energy use and makes the production process more sustainable,” Changzhu Wu explains.

While E. coli is often associated with foodborne illness, it is widely used in the pharmaceutical industry to produce essential medicines like insulin and growth hormone through various chemical reactions.

The industry uses vast quantities of E. coli, and replacing them takes a toll on the environment, energy, and time due to factors like high temperatures, extreme pH levels, UV radiation, and exposure to solvents.

In developing his “Superman cape,” Changzhu Wu sought a material that could envelop the bacteria while still allowing them to interact with their environment to carry out the desired complex chemical reactions.

The solution: a polymer coating that integrates with the bacterial cell membrane. Polymers are large molecules made up of billions of identical units called monomers.

“We essentially grafted an E. coli bacterium’s cell membrane with polymers, achieving two important outcomes: First, the bacteria became stronger and more efficient, and could carry out complex chemical reactions more quickly. Second, the bacteria became more protected, allowing for multiple uses. So, it’s a kind of ‘Superman bacterium’ that is more sustainable,” explains Changzhu Wu.

A new study in published in Scientific Reports suggests that the perfect cup of coffee is influenced by a complex blend of variables such as bean processing method, brewing time, and grind size, not just the roast level.

Caffeine content and extraction yield are two of the most vital variables for coffee enthusiasts, especially those who approach it with precision.

Extraction yield is a measure of the amount of soluble material from the coffee grounds that gets dissolved in the brewed coffee. It essentially reflects the efficiency of the brewing process in extracting compounds from the coffee grounds.

Led by Dr. Zachary R. Lindsey, Assistant Professor of Physics at Berry College, U.S., the study focuses on how the degree of roast affects these two variables. Phys.org spoke to Dr. Lindsey, a self-proclaimed coffee nerd about the study.

“Over 20 years ago, I heard a barista claim that dark roasts have more caffeine, but a decade later, I was exposed to the contrasting idea that light roasts were the king of caffeine. Yet, I couldn’t find any convincing data.”

“It wasn’t until I picked up coffee roasting as a hobby in 2022 that I started to see the missing pieces of the puzzle. Luckily, two passionate undergraduate students on my research team were also intrigued by this mystery, and we got to work,” said Dr. Lindsey.

Choice of coffee, roast, and brew method

The researchers chose Ethiopian coffee to conduct their study. Ethiopia has a long tradition of producing coffee dating back centuries as it is the country where Coffee arabica, aka the coffee plant, originates.

In this, they are investigating natural and washed processed coffee.

In the natural method, the coffee cherries are dried with the seeds still inside. The seeds are separated after drying, resulting in fruity and complex flavors in the coffee beans. On the other hand, in the washed method, the seeds are separated from the coffee cherries and then dried, leading to a cleaner and brighter flavor profile.

The researchers then used five different degrees of roasts for the green coffee beans, choosing a brewing time of one, two, and ten minutes.

The researchers chose the AeroPress brewing method with a 15:1 water-to-coffee ratio. The AeroPress is a pressure-based brewing method, similar to an espresso machine, but on a smaller scale. The AeroPress steeps the coffee and uses pressure to extract the brew through a paper filter.

Dr. Lindsey explained the choice behind the AeroPress, saying, “When selecting a brew method, the main goal was to implement a procedure that could consistently produce brews within a wide range of extraction yields by only varying the brew time.”

“The AeroPress stood out as a means to achieve these desired outcomes with minimal variation across all roast batches.”

Overall, the researchers had 30 unique combinations of brewed coffee to study.

Analyzing the coffee

The researchers used three analysis techniques to analyze caffeine content and extraction yield.

To measure compounds like caffeine, chlorogenic acids, and other soluble compounds in the brewed coffee, they used high-performance liquid chromatography (HPLC).

This method separates different compounds in the coffee based on their interactions with a standard material, quantifying individual concentrations.

Next, they used refractometry. This method measures the bending of light through the brewed coffee, indicating the extraction yield, i.e., how much soluble material is dissolved from the coffee grounds.

Finally, they used scanning electron microscopy (SEM) to observe the surface of the coffee beans and grounds. This helped them to examine the grain size and porosity. SEM provides information about the impact of roasting on the physical features of the coffee beans.

“SEM allows for a straightforward characterization approach that provides two-dimensional information about the structure of the roasted coffee. The evolving porosity of the roasting coffee plays a pivotal role in compound mobility during roasting and brewing,” explained Dr. Lindsey.

Porosity, caffeine, and extraction

The researchers found that caffeine content in the brewed coffee depended on the roasting process and the extraction yield.

“During roasting, the volume and porosity of the coffee seeds increase as the roast progresses, which makes it easier for compounds to move in or out of the system,” explained Dr. Lindsey.

A greater porosity implies more of the inner surface area of the coffee grounds is exposed, making it easier for water to penetrate and dissolve compounds like caffeine and flavors. This has an impact on the entire extraction process that occurs during brewing.

For the caffeine content, the researchers found that when using identical brewing setups, light and medium roasts had a higher caffeine content than darker roasts. This is due to the caffeine loss during roasting, resulting in typically lower extraction yields for darker roasts.

Conversely, they found that the darker roast’s caffeine content was higher when the extraction yield was kept consistent for all the roasts.

“However, darker roasts consistently exhibited lower extraction yields than light and medium roasts, so it was not always possible to achieve a common extraction yield for all degrees of roast,” added Dr. Lindsey.

New insights

The competing mechanisms of increased porosity improving extraction efficiency and darker roasts losing extractable compounds revealed a unique insight contradicting previous assumptions.

Caffeine sublimation—the process of caffeine transitioning directly from a solid to a gas—occurs at higher temperatures than previously thought.

“Although the interplay between roast degree and caffeine content has been addressed over 20 times in the literature, the prevailing theory is that caffeine remains stable during the roasting process.”

“However, we establish a clear relationship between roast degree, caffeine content, and extraction yield,” said Dr. Lindsey.

The researchers plan to extend this work to study the relationship between roast degree and extraction yield for decaffeinated coffees. They also aim to test it with percolation-based brewing methods to see if they yield similar results.

The bottom line is, if you want a cup of coffee with the maximum caffeine content choose a medium roast, says Dr. Lindsey.

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