Enlarge/ UNSW Sydney engineers developed a new way to make cold brew coffee in under three minutes without sacrificing taste.
University of New South Wales, Sydney
Diehard fans of cold-brew coffee put in a lot of time and effort for their preferred caffeinated beverage. But engineers at the University of New South Wales, Sydney, figured out a nifty hack. They rejiggered an existing espresso machine to accommodate an ultrasonic transducer to administer ultrasonic pulses, thereby reducing the brewing time from 12 to 24 hours to just under three minutes, according to a new paper published in the journal Ultrasonics Sonochemistry.
As previously reported, rather than pouring boiling or near-boiling water over coffee grounds and steeping for a few minutes, the cold-brew method involves mixing coffee grounds with room-temperature water and letting the mixture steep for anywhere from several hours to two days. Then it is strained through a sieve to filter out all the sludge-like solids, followed by filtering. This can be done at home in a Mason jar, or you can get fancy and use a French press or a more elaborate Toddy system. It’s not necessarily served cold (although it can be)—just brewed cold.
The result is coffee that tastes less bitter than traditionally brewed coffee. “There’s nothing like it,” co-author Francisco Trujillo of UNSW Sydney told New Scientist. “The flavor is nice, the aroma is nice and the mouthfeel is more viscous and there’s less bitterness than a regular espresso shot. And it has a level of acidity that people seem to like. It’s now my favorite way to drink coffee.”
While there have been plenty of scientific studies delving into the chemistry of coffee, only a handful have focused specifically on cold-brew coffee. For instance, a 2018 study by scientists at Thomas Jefferson University in Philadelphia involved measuring levels of acidity and antioxidants in batches of cold- and hot-brew coffee. But those experiments only used lightly roasted coffee beans. The degree of roasting (temperature) makes a significant difference when it comes to hot-brew coffee. Might the same be true for cold-brew coffee?
To find out, the same team decided in 2020 to explore the extraction yields of light-, medium-, and dark-roast coffee beans during the cold-brew process. They used the cold-brew recipe from The New York Times for their experiments, with a water-to-coffee ratio of 10:1 for both cold- and hot-brew batches. (Hot brew normally has a water-to-coffee ratio of 20:1, but the team wanted to control variables as much as possible.) They carefully controlled when water was added to the coffee grounds, how long to shake (or stir) the solution, and how best to press the cold-brew coffee.
The team found that for the lighter roasts, caffeine content and antioxidant levels were roughly the same in both the hot- and cold-brew batches. However, there were significant differences between the two methods when medium- and dark-roast coffee beans were used. Specifically, the hot-brew method extracts more antioxidants from the grind; the darker the bean, the greater the difference. Both hot- and cold-brew batches become less acidic the darker the roast.
Enlarge/ The new faster cold brew system subjects coffee grounds in the filter basket to ultrasonic sound waves from a transducer, via a specially adapted horn.
UNSW/Francisco Trujillo
That gives cold brew fans a few handy tips, but the process remains incredibly time-consuming; only true aficionados have the patience required to cold brew their own morning cuppa. Many coffee houses now offer cold brews, but it requires expensive, large semi-industrial brewing units and a good deal of refrigeration space. According to Trujillo, the inspiration for using ultrasound to speed up the process arose from failed research attempts to extract more antioxidants. Those experiments ultimately failed, but the setup produced very good coffee.
Trujillo et al. used a Breville Dual Boiler BES920 espresso machine for their latest experiments, with a few key modifications. They connected a bolt-clawed transducer to the brewing basket with a metal horn. They then used the transducer to inject 38.8 kHz sound waves through the walls at several different points, thereby transforming the filter basket into a powerful ultrasonic reactor.
The team used the machine’s original boiler but set it up to be independently controlled it with an integrated circuit to better manage the temperature of the water. As for the coffee beans, they picked Campos Coffee’s Caramel & Rich Blend (a medium roast). “This blend combines fresh, high-quality specialty coffee beans from Ethiopia, Kenya, and Colombia, and the roasted beans deliver sweet caramel, butterscotch, and milk chocolate flavors,” the authors wrote.
There were three types of samples for the experiments: cold brew hit with ultrasound at room temperature for one minute or for three minutes, and cold brew prepared with the usual 24-hour process. For the ultrasonic brews, the beans were ground into a fine grind typical for espresso, while a slightly coarser grind was used for the traditional cold-brew coffee.
One reason plastic waste persists in the environment is because there’s not much that can eat it. The chemical structure of most polymers is stable and different enough from existing food sources that bacteria didn’t have enzymes that could digest them. Evolution has started to change that situation, though, and a number of strains have been identified that can digest some common plastics.
An international team of researchers has decided to take advantage of those strains and bundle plastic-eating bacteria into the plastic. To keep them from eating it while it’s in use, the bacteria is mixed in as inactive spores that should (mostly—more on this below) only start digesting the plastic once it’s released into the environment. To get this to work, the researchers had to evolve a bacterial strain that could tolerate the manufacturing process. It turns out that the evolved bacteria made the plastic even stronger.
Bacteria meet plastics
Plastics are formed of polymers, long chains of identical molecules linked together by chemical bonds. While they can be broken down chemically, the process is often energy-intensive and doesn’t leave useful chemicals behind. One alternative is to get bacteria to do it for us. If they’ve got an enzyme that breaks the chemical bonds of a polymer, they can often use the resulting small molecules as an energy source.
The problem has been that the chemical linkages in the polymers are often distinct from the chemicals that living things have come across in the past, so enzymes that break down polymers have been rare. But, with dozens of years of exposure to plastics, that’s starting to change, and a number of plastic-eating bacterial strains have been discovered recently.
This breakdown process still requires that the bacteria and plastics find each other in the environment, though. So a team of researchers decided to put the bacteria in the plastic itself.
The plastic they worked with is called thermoplastic polyurethane (TPU), something you can find everywhere from bicycle inner tubes to the coating on your ethernet cables. Conveniently, there are already bacteria that have been identified that can break down TPU, including a species called Bacillus subtilis, a harmless soil bacterium that has also colonized our digestive tracts. B. subtilis also has a feature that makes it very useful for this work: It forms spores.
This feature handles one of the biggest problems with incorporating bacteria into materials: The materials often don’t provide an environment where living things can thrive. Spores, on the other hand, are used by bacteria to wait out otherwise intolerable conditions, and then return to normal growth when things improve. The idea behind the new work is that B. subtilis spores remain in suspended animation while the TPU is in use and then re-activate and digest it once it’s disposed of.
In practical terms, this works because spores only reactivate once nutritional conditions are sufficiently promising. An Ethernet cable or the inside of a bike tire is unlikely to see conditions that will wake the bacteria. But if that same TPU ends up in a landfill or even the side of the road, nutrients in the soil could trigger the spores to get to work digesting it.
The researchers’ initial problem was that the manufacturing of TPU products usually involves extruding the plastic at high temperatures, which are normally used to kill bacteria. In this case, they found that a typical manufacturing temperature (130° C) killed over 90 percent of the B. subtilis spores in just one minute.
So, they started out by exposing B. subtilis spores to lower temperatures and short periods of heat that were enough to kill most of the bacteria. The survivors were grown up, made to sporulate, and then exposed to a slightly longer period of heat or even higher temperatures. Over time, B. subtilis evolved the ability to tolerate a half hour of temperatures that would kill most of the original strain. The resulting strain was then incorporated into TPU, which was then formed into plastics through a normal extrusion process.
You might expect that putting a bunch of biological material into a plastic would weaken it. But the opposite turned out to be true, as various measures of its tensile strength showed that the spore-containing plastic was stronger than pure plastic. It turns out that the spores have a water-repelling surface that interacts strongly with the polymer strands in the plastic. The heat-resistant strain of bacteria repelled water even more strongly, and plastics made with these spores was tougher still.
To simulate landfilling or litter with the plastic, the researchers placed them in compost. Even without any bacteria, there were organisms present that could degrade it; by five months in the compost, plain TPU lost nearly half its mass. But with B. subtilis spores incorporated, the plastic lost 93 percent of its mass over the same time period.
This doesn’t mean our plastics problem is solved. Obviously, TPU breaks down relatively easily. There are lots of plastics that don’t break down significantly, and may not be compatible with incorporating bacterial spores. In addition, it’s possible that some TPU uses would expose the plastic to environments that would activate the spores—something like food handling or buried cabling. Still, it’s possible this new breakdown process can provide a solution in some cases, making it worth exploring further.
True wine aficionados might turn up their noses, but canned wines are growing in popularity, particularly among younger crowds during the summer months, when style often takes a back seat to convenience. Yet these same wines can go bad rather quickly, taking on distinctly displeasing notes of rotten eggs or dirty socks. Scientists at Cornell University conducted a study of all the relevant compounds and came up with a few helpful tips for frustrated winemakers to keep canned wines from spoiling. The researchers outlined their findings in a recent paper published in the American Journal of Enology and Viticulture.
“The current generation of wine consumers coming of age now, they want a beverage that’s portable and they can bring with them to drink at a concert or take to the pool,” said Gavin Sacks, a food chemist at Cornell. “That doesn’t really describe a cork-finished, glass-packaged wine. However, it describes a can very nicely.”
According to a 2004 article in Wine & Vines magazine, canned beer first appeared in the US in 1935, and three US wineries tried to follow suit for the next three years. Those efforts failed because it proved to be unusually challenging to produce a stable canned wine. One batch was tainted by “Fresno mold“; another batch resulted in cloudy wine within just two months; and the third batch of wine had a disastrous combination of low pH and high oxygen content, causing the wine to eat tiny holes in the cans. Nonetheless, wineries sporadically kept trying to can their product over the ensuing decades, with failed attempts in the 1950s and 1970s. United and Delta Airlines briefly had a short-lived partnership with wineries for canned wine in the early 1980s, but passengers balked at the notion.
The biggest issue was the plastic coating used to line the aluminum cans. You needed the lining because the wine would otherwise chemically react with the aluminum. But the plastic liners degraded quickly, and the wine would soon reek of dirty socks or rotten eggs, thanks to high concentrations of hydrogen sulfide. The canned wines also didn’t have much longevity, with a shelf life of just six months.
Thanks to vastly improved packing processes in the early 2000s, canned wine seems to finally be finding its niche in the market, initially driven by demand in Japan and other Asian markets and expanding after 2014 to Australia, New Zealand, the US, and the UK. In the US alone, projected sales of canned wines are expected to grow from $643 million in 2024 to $3.12 billion in 2034—a compound annual growth rate of 10.5 percent.
Granted, we won’t be seeing a fine Bordeaux in a can anytime soon; most canned wine comes in the form of spritzers, wine coolers, and cheaper rosés, whites, or sparkling wines. The largest US producers are EJ Gallo, which sells Barefoot Refresh Spritzers, and Francis Ford Coppola Winery, which markets the Sofia Mini, Underwood, and Babe brands.
Enlarge/ Locations within the body of a can sampled for liner and surface analysis.
M.J. Sheehan et al., 2024
There are plenty of oft-cited advantages to putting wine in cans. It’s super practical for picnics, camping, summer BBQs, or days at the beach, for example, and for the weight-conscious, it helps with portion control, since you don’t have to open an entire bottle. Canned wines are also touted as having a lower carbon footprint compared to glass—although that is a tricky calculation—and the aluminum is 100 percent recyclable.
This latest study grew out of a conference session Sacks led that was designed to help local winemakers get a better grasp on how best to protect the aromas, flavors, and shelf life of their canned wines since canned wines are still plagued by issues of corrosion, leakage, and off flavors like the dreaded rotten egg smell. “They said, ‘We’re following all the recommendations from the can suppliers and we still have these problems, can you help us out?’” Sacks said. “The initial focus was defining what the problem compounds were, what was causing corrosion and off aromas, and why was this happening in wines, but not in sodas? Why doesn’t Coca-Cola have a problem?”
Enlarge/ Active geology could have helped purify key chemicals needed for life.
Christof B. Mast
In some ways, the origin of life is looking much less mystifying than it was a few decades ago. Researchers have figured out how some of the fundamental molecules needed for life can form via reactions that start with extremely simple chemicals that were likely to have been present on the early Earth. (We’ve covered at least one of many examples of this sort of work.)
But that research has led to somewhat subtler but no less challenging questions. While these reactions will form key components of DNA and protein, those are often just one part of a complicated mix of reaction products. And often, to get something truly biologically relevant, they’ll have to react with some other molecules, each of which is part of its own complicated mix of reaction products. By the time these are all brought together, the key molecules may only represent a tiny fraction of the total list of chemicals present.
So, forming a more life-like chemistry still seems like a challenge. But a group of German chemists is now suggesting that the Earth itself provides a solution. Warm fluids moving through tiny fissures in rocks can potentially separate out mixes of chemicals, enriching some individual chemicals by three orders of magnitude.
Feeling the heat (and the solvent)
Even in the lab, it’s relatively rare for chemical reactions to produce just a single product. But there are lots of ways to purify out exactly what you want. Even closely related chemicals will often differ in their solubility in different solvents and in their tendency to stick to various glasses or ceramics, etc. The temperature can also influence all of those. So, chemists can use these properties as tools to fish a specific chemical out of a reaction mixture.
But, as far as the history of life is concerned, chemists are a relatively recent development—they weren’t available to purify important chemicals back before life had gotten started. Which raises the question of how the chemical building blocks of life ever reached the sorts of concentrations needed to do anything interesting.
The key insight behind this new work is that something similar to lab equipment exists naturally on Earth. Many rocks are laced with cracks, channels, and fissures that allow fluid to flow through them. In geologically active areas, that fluid is often warm, creating temperature gradients as it flows away from the heat source. And, as fluid moves through different rock types, the chemical environment changes. The walls of the fissures will have different chemical properties, and different salts may end up dissolved in the fluid.
All of that can provide conditions where some chemicals move more rapidly through the fluid, while others tend to stay where they started. And that has the potential to separate out key chemicals from the reaction mixes that produce the components of life.
But having the potential is very different from clearly working. So, the researchers decided to put the idea to the test.
Explore the chemistry behind making a cocktail with curdled milk, aka milk washing—like Ben Franklin’s fave, milk punch.
It’s well-known that Benjamin Franklin was a Founding Father who enjoyed a nice tipple or two (or three). One of his favorite alcoholic beverages was milk punch, a heady concoction of brandy, lemon juice, nutmeg, sugar, water, and hot whole milk—the latter nicely curdled thanks to the heat, lemon juice, and alcohol. It employs a technique known as “milk washing,” used to round out and remove harsh, bitter flavors from spirits that have been less than perfectly distilled, as well as preventing drinks from spoiling (a considerable benefit in the 1700s).
Some versions of milk punch also incorporate tea, and in the mixed drink taxonomy, it falls somewhere between a posset and syllabub. The American Chemical Society’s George Zaidan decided to delve a bit deeper into the chemistry behind milk washing in a new Reactions video after tasting the difference between a Tea Time cocktail made with the milk washing method and one made without it. The latter was so astringent, it was “like drinking a cup of tea that’s been brewed for 6,000 years,” per Zaidan. In the process, he ended up stumbling onto a flavorful new twist on the classic espresso martini (although martini purists probably wouldn’t consider either to be a true martini).
There isn’t anything in the scientific literature about milk washing as it specifically pertains to cocktails, so Zaidan broke the process down into three simple experiments, armed with all the necessary ingredients and his trusty centrifuge. First, he combined whole milk with Coke, a highly acidic beverage that curdles the milk. Per Zaidan, this happens because of the casein proteins in milk, which typically have an overall negative charge that keeps them from clumping. Adding the acid (Coke) adds protons to the mix so that it is electrically neutral (usually at a pH of 4.6).
At that point, the caseins clump together to form solid fatty curds surrounded by a watery liquid. That liquid is significantly lighter than the original Coke because the curds absorbed all the molecules that give the beverage its color. “They’re particularly good at pulling tannins, which are those astringent bitter mouth-puckering molecules, out of stuff,” Zaidan said. The liquid remained sweet, since the curds don’t absorb the sugar, but the taste was now more akin to Sprite. The curds didn’t taste much like Coke either.
Enlarge/ Benjamin Franklin’s recipe for milk punch, included in a 1763 letter to James Bowdoin.
Next, Zaidan conducted an experiment to see whether vodka can absorb the rich fatty flavors of butter and ghee (clarified butter), aka “fat washing,” which should be extendable to other fats like bacon and peanut butter. It took 24 hours to accomplish, but both the butter- and ghee-infused vodkas received a thumbs-up during the taste test. According to Zaidan, this demonstrates that milk washing adds buttery flavor and texture to a cocktail in addition to removing flavor (notably bitter compounds) and color.
But what about the whey, the other type of milk protein? Per Zaidan, this makes for a nice secret ingredient to add to a milk washed cocktail, based on his experiment combining whey with vodka. It doesn’t seem to have much impact on the vodka’s flavor but it adds a pleasant texture and smoother mouth feel as it coats the tongue.
Armed with his three deconstructed components of the milk washing process, Zaidan was ready to create his own twist on a classic cocktail. First, he poured vodka over peanut butter to infuse the fatty flavor into the spirits (fat washing). Then he curdled some milk and added it to espresso to temper the latter’s bitter flavors and combined it with the peanut butter-infused vodka. Finally, he added Kahlua, simple syrup, and a bit of whey for extra body and texture.
Voila! You’ve got a tastier, more complex version (per Zaidan) of an espresso martini. The downside: It’s an extremely time-consuming cocktail to make. Perhaps that’s why Franklin’s original recipe for milk punch was clearly meant to be made in bulk. (The Massachusetts Historical Society’s modern interpretation cuts the portions by three-quarters.)
Listing image by YouTube/American Chemical Society
Enlarge/ Scientists at the University of Nottingham have discovered how to create different colors of blue cheese.
University of Nottingham
Gourmands are well aware of the many varieties of blue cheese, known by the blue-green veins that ripple through the cheese. Different kinds of blue cheese have distinctive flavor profiles: they can be mild or strong, sweet or salty, for example. Soon we might be able to buy blue cheeses that belie the name and sport veins of different colors: perhaps yellow-green, reddish-brown-pink, or lighter/darker shades of blue, according to a recent paper published in the journal Science of Food.
“We’ve been interested in cheese fungi for over 10 years, and traditionally when you develop mould-ripened cheeses, you get blue cheeses such as Stilton, Roquefort, and Gorgonzola, which use fixed strains of fungi that are blue-green in color,” said co-author Paul Dyer of the University of Nottingham of this latest research. “We wanted to see if we could develop new strains with new flavors and appearances.”
Blue cheese has been around for a very long time. Legend has it that a young boy left his bread and ewe’s milk cheese in a nearby cave to pursue a lovely young lady he’d spotted in the distance. Months later, he came back to the cave and found it had molded into Roquefort. It’s a fanciful tale, but scholars think the basic idea is sound: people used to store cheeses in caves because their temperature and moisture levels were especially hospitable to harmless molds. That was bolstered by a 2021 analysis of paleofeces that found evidence that Iron Age salt miners in Hallstatt (Austria) between 800 and 400 BCE were already eating blue cheese and quaffing beer.
The manufacturing process for blue cheese is largely the same as for any cheese, with a few crucial additional steps. It requires cultivation of Penicillium roqueforti, a mold that thrives on exposure to oxygen. The P. roqueforti is added to the cheese, sometimes before curds form and sometimes mixed in with curds after they form. The cheese is then aged in a temperature-controlled environment. Lactic acid bacteria trigger the initial fermentation but eventually die off, and the P. roqueforti take over as secondary fermenters. Piercing the curds forms air tunnels in the cheese, and the mold grows along those surfaces to produce blue cheese’s signature veining.
Once scientists published the complete genome for P. roqueforti, it opened up opportunities for studying this blue cheese fungus, per Dyer et al. Different strains “can have different colony cultures and textures, with commercial strains being sold partly on the basis of color development,” they wrote. This coloration comes from pigments in the coatings of the spores that form as the colony grows. Dyer and his co-authors set out to determine the genetic basis of this pigment formation in the hopes of producing altered strains with different spore coat colors.
The team identified a specific biochemical pathway, beginning with a white color that gradually goes from yellow-green, red-brown-pink, dark brown, light blue, and ultimately that iconic dark blue-green. They used targeted gene deletion to block pigment biosynthesis genes at various points in this pathway. This altered the spore color, providing a proof of principle without adversely affecting the production of flavor volatiles and levels of secondary metabolites called mycotoxins. (The latter are present in low enough concentrations in blue cheese so as not to be a health risk for humans, and the team wanted to ensure those concentrations remained low.)
Enlarge/ (left) Spectrum of color strains produced in Pencillium roqueforti. (right) Cross sections of cheeses made with the original (dark blue-green) or new color (red-brown, bright green, white albino) strains of the fungus.
University of Nottingham
However, food industry regulations prohibit gene-deletion fungal strains for commercial cheese production. So Dyer et al. used UV mutagenesis—essentially “inducing sexual reproduction in the fungus,” per Dyer—to produce non-GMO mutant strains of the fungi to create “blue” cheeses of different colors, without increasing mycotoxin levels or impacting the volatile compounds responsible for flavor.
“The interesting part was that once we went on to make some cheese, we then did some taste trials with volunteers from across the wider university, and we found that when people were trying the lighter colored strains they thought they tasted more mild,” said Dyer. “Whereas they thought the darker strain had a more intense flavor. Similarly, with the more reddish-brown and a light green one, people thought they had a fruity, tangy element to them—whereas, according to the lab instruments, they were very similar in flavor. This shows that people do perceive taste not only from what they taste but also by what they see.”
Dyer’s team is hoping to work with local cheese makers in Nottingham and Scotland, setting up a spinoff company in hopes of commercializing the mutant strains. And there could be other modifications on the horizon. “Producers could almost dial up their list of desirable characteristics—more or less color, faster or slower growth rate, acidity differences,” Donald Glover of the University of Queensland in Australia, who was not involved in the research, told New Scientist.
The metals that form the foundation of modern society also cause a number of problems. Separating the metals we want from other minerals is often energy-intensive and can leave behind large volumes of toxic waste. Getting them in a pure form can often require a second and considerable energy input, boosting the associated carbon emissions.
A team of researchers from Germany has now figured out how to handle some of these problems for a specific class of mining waste created during aluminum production. Their method relies on hydrogen and electricity, which can both be sourced from renewable power and extracts iron and potentially other metals from the waste. What’s left behind may still be toxic but isn’t as environmentally damaging.
Out of the mud
The first step in aluminum production is the isolation of aluminum oxide from the other materials in the ore. This leaves behind a material known as red mud; it’s estimated that nearly 200 million tonnes are produced annually. While the red color comes from the iron oxides present, there are a lot of other materials in it, some of which can be toxic. And the process of isolating the aluminum oxide leaves the material with a very basic pH.
All of these features mean that the red mud generally can’t (or at least shouldn’t) be returned to the environment. It’s generally kept in containment ponds—globally, these are estimated to house 4 billion tonnes of red mud, and many containment pods have burst over the years.
The iron oxides can account for over half the weight of red mud in some locations, potentially making it a good source of iron. Traditional methods have processed iron ores by reacting them with carbon, leading to the release of carbon dioxide. But there have been efforts made to develop “green steel” production in which this step is replaced by a reaction with hydrogen, leaving water as the primary byproduct. Since hydrogen can be made from water using renewable electricity, this has the potential to eliminate a lot of the carbon emissions associated with iron production.
The team from Germany decided to test a method of green steel production on red mud. They heated some of the material in an electric arc furnace under an atmosphere that was mostly argon (which wouldn’t react with anything) and hydrogen (at 10 percent of the mix).
Pumping (out) iron
The reaction was remarkably quick. Within a few minutes, metallic iron nodules started appearing in the mixture. The iron production was largely complete by about 10 minutes. The iron was remarkably pure, at about 98 percent of the material by weight in the nodules being iron.
Starting with a 15-gram sample of red mud, the process reduced this to 8.8 grams, as lots of the oxygen in the material was liberated in the form of water. (It’s worth noting that this water could be cycled back to hydrogen production, closing the loop on this aspect of the process.) Of that 8.8 grams, about 2.6 (30 percent) was in the form of iron.
The research found that there are also some small bits of relatively pure titanium formed in the mix. So, there’s a chance that this can be used in the production of additional metals, although the process would probably need to be optimized to boost the yield of anything other than iron.
The good news is that there’s much less red mud left to worry about after this. Depending on the source of the original aluminum-containing ore, some of this may include relatively high concentrations of valuable materials, such as rare earth minerals. The downside is that any toxic materials in the original ore are going to be significantly more concentrated.
As a small plus, the process also neutralizes the pH of the remaining residue. So, that’s at least one less thing to worry about.
The downside is that the process is incredibly energy-intensive, both in producing the hydrogen required and running the arc furnace. The cost of that energy makes things economically challenging. That’s partly offset by the lower processing costs—the ore has already been obtained and has a relatively high purity.
But the key feature of this is the extremely low carbon emissions. Right now, there’s no price on those in most countries, which makes the economics of this process far more difficult.
There’s rarely time to write about every cool science-y story that comes our way. So this year, we’re once again running a special Twelve Days of Christmas series of posts, highlighting one science story that fell through the cracks in 2020, each day from December 25 through January 5. Today: Archaeologists relied on chemical clues and techniques like FTIR spectroscopy and archaeomagnetic analysis to reconstruct the burning of Jerusalem by Babylonian forces around 586 BCE.
Archaeologists have uncovered new evidence in support of Biblical accounts of the siege and burning of the city of Jerusalem by the Babylonians around 586 BCE, according to a September paper published in the Journal of Archaeological Science.
The Hebrew bible contains the only account of this momentous event, which included the destruction of Solomon’s Temple. “The Babylonian chronicles from these years were not preserved,” co-author Nitsan Shalom of Tel Aviv University in Israel told New Scientist. According to the biblical account, “There was a violent and complete destruction, the whole city was burned and it stayed completely empty, like the descriptions you see in [the Book of] Lamentations about the city deserted and in complete misery.”
Judah was a vassal kingdom of Babylon during the late 7th century BCE, under the rule of Nebuchadnezzar II. This did not sit well with Judah’s king, Jehoiakim, who revolted against the Babylonian king in 601 BCE despite being warned not to do so by the prophet Jeremiah. He stopped paying the required tribute and sided with Egypt when Nebuchadnezzar tried (and failed) to in invade that country. Jehoiakim died and his son Jeconiah succeeded him when Nebuchadnezzar’s forces besieged Jerusalem in 597 BCE. The city was pillaged and Jeconiah surrendered and was deported to Babylon for his trouble, along with a substantial portion of Judah’s population. (The Book of Kings puts the number at 10,000.) His uncle Zedekiah became king of Judah.
Zedekiah also chafed under Babylonian rule and revolted in turn, refusing to pay the required tribute and seeking alliance with the Egyptian pharaoh Hophra. This resulted in a brutal 30-month siege by Nebuchadnezzar’s forces against Judah and its capital, Jerusalem. Eventually the Babylonians prevailed again, breaking through the city walls to conquer Jerusalem. Zedekiah was forced to watch his sons killed and was then blinded, bound, and taken to Babylon as a prisoner. This time Nebuchadnezzar was less merciful and ordered his troops to completely destroy Jerusalem and pull down the wall around 586 BCE.
There is archaeological evidence to support the account of the city being destroyed by fire, along with nearby villages and towns on the western border. Three residential structures were excavated between 1978 and 1982 and found to contain burned wooden beams dating to around 586 BCE. Archaeologists also found ash and burned wooden beams from the same time period when they excavated several structures at the Giv’ati Parking Lot archaeological site, close to the assumed location of Solomon’s Temple. Samples taken from a plaster floor showed exposure to high temperatures of at least 600 degrees Celsius
Enlarge/ Aerial view of the excavation site in Jerusalem, at the foot of the Temple Mount
Assaf Peretz/Israel Antiquities Authority
However, it wasn’t possible to determine from that evidence whether the fires were intentional or accidental, or where the fire started if it was indeed intentional. For this latest research, Shalom and her colleagues focused on the two-story Building 100 at the Giv’ati Parking Lot site. They used Fourier transform infrared (FTIR) spectroscopy—which measures the absorption of infrared light to determine to what degree a sample had been heated—and archaeomagnetic analysis, which determines whether samples containing magnetic minerals were sufficiently heated to reorient those compounds to a new magnetic north.
The analysis revealed varying degrees of exposure to high-temperature fire in three rooms (designated A, B, and C) on the bottom level of Building 100, with Room C showing the most obvious evidence. This might have been a sign that Room C was the ignition point, but there was no fire path; the burning of Room C appeared to be isolated. Combined with an earlier 2020 study on segments of the second level of the building, the authors concluded that several fires were lit in the building and the fires burned strongest in the upper floors, except for that “intense local fire” in Room C on the first level.
“When a structure burns, heat rises and is concentrated below the ceiling,” the authors wrote. “The walls and roof are therefore heated to higher temperatures than the floor.” The presence of charred beams on the floors suggest this was indeed the case: most of the heat rose to the ceiling, burning the beams until they collapsed to the floors, which otherwise were subjected to radiant heat. But the extent of the debris was likely not caused just by that collapse, suggesting that the Babylonians deliberately went back in and knocked down any remaining walls.
Furthermore, “They targeted the more important, the more famous buildings in the city,” Shalom told New Scientist, rather than destroying everything indiscriminately. “2600 years later, we’re still mourning the temple.”
While they found no evidence of additional fuels that might have served as accelerants, “we may assume the fire was intentionally ignited due to its widespread presence in all rooms and both stories of the building,” Shalom et al. concluded. “The finds within the rooms indicate there was enough flammable material (vegetal and wooden items and construction material) to make additional fuel unnecessary. The widespread presence of charred remains suggests a deliberate destruction by fire…. [T]he spread of the fire and the rapid collapse of the building indicate that the destroyers invested great efforts to completely demolish the building and take it out of use.”
Enlarge/ The Royal Institution was founded in 1799 and is still located in the same historic building at 21 Albermarle Street in London.
If you’re a fan of science, and especially science history, no trip to London is complete without visiting the Royal Institution, browsing the extensive collection of artifacts housed in the Faraday Museum and perhaps taking in an evening lecture by one of the many esteemed scientists routinely featured—including the hugely popular annual Christmas lectures. (The lecture theater may have been overhauled to meet the needs of the 21st century but walking inside still feels a bit like stepping back through time.) So what better time than the Christmas season to offer a virtual tour of some of the highlights contained within the historic walls of 21 Albemarle Street?
The Royal Institution was founded in 1799 by a group of leading British scientists. This is where Thomas Young explored the wave theory of light (at a time when the question of whether light was a particle or wave was hotly debated); John Tyndall conducted experiments in radiant heat; Lord Rayleigh discovered argon; James Dewar liquified hydrogen and invented the forerunner of the thermos; and father-and-son duo William Henry and William Lawrence Bragg invented x-ray crystallography.
No less than 14 Nobel laureates have conducted ground-breaking research at the Institution over the ensuing centuries, but the 19th century physicist Michael Faraday is a major focus. In fact, there is a full-sized replica of Faraday’s magnetic laboratory—where he made so many of his seminal discoveries—in the original basement room where he worked, complete with an old dumbwaiter from when the room was used as a servant’s hall. Its arrangement is based on an 1850s painting by one of Faraday’s friends and the room is filled with objects used by Faraday over the course of his scientific career.
The son of an English blacksmith, Faraday was apprenticed to a bookbinder at 14, a choice of profession that enabled him to read voraciously, particularly about the natural sciences. In 1813, a friend gave Faraday a ticket to hear the eminent scientist Humphry Davy lecture on electrochemistry at the Royal Institution. He was so taken by the presentation that he asked Davy to hire him. Davy initially declined, but shortly afterwards sacked his assistant for brawling, and hired Faraday to replace him. Faraday helped discover two new compounds of chlorine and carbon in those early days, learned how to make his own glass, and also invented an early version of the Bunsen burner, among other accomplishments.
Painting of the Royal Institution circa 1838, by Thomas Hosmer Shepherd.
Public domain
Michael Faraday giving one of his famous Christmas lectures.
Royal Institution
A Friday Evening Discourse at the Royal Institution; Sir James Dewar on Liquid Hydrogen, by Henry Jamyn Brooks, 1904
Public domain
The Lecture Theatre as it looks today
Faraday’s magnetic laboratory in the basement of the Royal Institution
Royal Institution
A page from one of Faraday’s notebooks
Royal Institution
Faraday was particularly interested in the new science of electromagnetism, first discovered in 1820 by Hans Christian Ørsted. In 1821, Faraday discovered electromagnetic rotation—which converts electricity into mechanical motion via a magnet—and used that underlying principle to build the first electric motor. The Royal Institution’s collection includes the only surviving electric motor that Faraday built: a wire hanging down into a glass vessel with a bar magnet at the bottom. Faraday would fill the glass with mercury (an excellent conductor), then connect his apparatus to a battery, which sent electricity through the wire in turn. This created a magnetic field around the wire, and that field’s interaction with the magnet at the bottom of the glass vessel would cause the wire to rotate in a clockwise direction.
Ten years later, Faraday succeeded in showing that a jiggling magnet could induce an electrical current in a wire. Known as the principle of the dynamo, or electromagnetic induction, it became the basis of electric generators, which convert the energy of a changing magnetic field into an electrical current. One of Faraday’s induction rings is on display, comprised of coils of wire wound on opposites sides of the ring, insulated with cotton. Passing electricity through one would briefly induce a current in the other. Also on display is one of Faraday’s generators: a bar magnet and a simple cotton-insulated tube wound with a coil of wire.
In yet another experiment, Faraday placed a piece of heavy leaded glass on a magnet’s poles to see how light would be affected by a magnet. He passed light through the glass and when he turned on the electromagnet, he found that the polarization of the light had rotated slightly. This is called the magneto-optical effect (or Faraday effect), demonstrating that magnetism is related not just to electricity, but also to light. The Royal Institution has a Faraday magneto-optical apparatus with which he “at last succeeded in… magnetizing a ray of light.” In 1845, Faraday discovered diamagnetism, a property of certain materials that give them a weak repulsion from a magnetic field.
Equipment used by Faraday to make glass
Drawing of Faraday’s electromagnetic rotation experiment.
Public domain
Faraday motor (electric magnetic rotation apparatus), 1822
Royal Institution
Faraday’s dynamo (generator), October 1831
Royal Institution
Faraday’s induction ring
Royal Institution
Faraday’s magneto-optical apparatus
Royal Institution
One of Faraday’s iron filings (1851) showing magnetic lines of force
Royal Institution
Faraday’s original gold colloids are still active well over a century later
Shining a laser light through a gold colloid mixture produces the Faraday-Tyndall Effect.
Royal Institution
Faraday concluded from all those experiments that magnetism was the center of an elaborate system of invisible curved tentacles (electric lines of force) that spread throughout space like the roots of trees branching through the earth. He was able to demonstrate these lines of force by coating sheets of paper with wax and placing them on top of bar magnets. When he sprinkled powdery iron filings on the surface, those iron filings were attracted to the magnets, revealing the lines of force. And by gently heating the waxed paper, he found that the iron filings would set on the page, preserving them.
In the 1850s, Faraday’s interests turned to the properties of light and matter. He made his own gold slides and shone light through them to observe the interactions. But commercial gold leaf, typically made by hammering the metal into thin sheets, was still much too thick for his purposes. So Faraday had to make his own via chemical means, which involved washing gold films. The resulting faint red fluid intrigued Faraday and he kept samples in bottles, shining light though the fluids and noting an intriguing “cone effect” (now known as the Faraday-Tyndall Effect)—the result of particles of gold suspended in the fluid that were much too small to see.
One might consider Faraday an early nanoscientist, since these are now known as metallic nanoparticles. The Institution’s current state-of-the-art nanotechnology lab is appropriately located right across from Faraday’s laboratory in the basement. And even though Faraday’s gold colloids are well over a century old, they remain optically active. There’s no way to figure out why this might be the case without opening the bottles but the bottles are too valuable as artifacts to justify doing that.
Plenty of other scientific luminaries have their work commemorated in the Royal Institution’s collection, including that of Faraday’s mentor, Humphry Davy, who discovered the chemical elements barium, strontium, sodium, potassium, calcium and magnesium. Early in the 19th century, there were several explosions in northern England’s coal mines caused by the lamps used by the miners accidentally igniting pockets of flammable gas. Davy was asked to come up with a safer lighting alternative.
Schematic for the Davy lamp
Public domain
Humphry Davy’s miner’s lamp (left) displayed alongside his rival George Stephenson’s lamps
Royal Institution
Schematic for John Tyndall’s radiant heat apparatus
Royal Institution
Tyndall’s radiant heat tube
Royal Institution
Tyndall’s blue sky tube, 1869
Royal Institution
Title page of Tyndall’s Heat: A Mode of Motion
Paul Wilkinson/Royal Institution
After experimenting with several prototypes, Davy finally settled on a simple design in 1815 consisting of a “chimney” made of wire gauze to enclose the flame. The gauze absorbed heat to prevent igniting flammable gas but still let through sufficient light. The invention significantly reduced fatalities among coal miners. Davy had a rival, however in a mining engineer named George Stephenson who independently developed his own design that was remarkably similar to Davy’s. Samples of both are displayed in the Institution’s lower ground floor “Light Corridor.” Davy’s lamp would ultimately triumph, while Stephenson later invented the first steam-powered railroad locomotive.
Atmospheric physicist John Tyndall was a good friend of Faraday and shared the latter’s gift for public lecture demonstrations. His experiments on radiation and the heat-absorptive power of gases were undertaken with an eye toward developing a better understanding of the physics of molecules. Among the Tyndall artifacts housed in the Royal Institution is his radiant heat tube, part of an elaborate experimental apparatus he used to measure the extent to which infrared radiation was absorbed and emitted by various gases filling its central tube. By this means he concluded that water vapor absorbs more radiant heat than atmospheric gases, and hence that vapor is crucial for moderating Earth’s climate via a natural “greenhouse effect.”
The collection also includes Tyndall’s “blue sky apparatus,” which the scientist used to explain why the sky is blue during the day and takes on red hues at sunset—namely, particles in the Earth’s atmosphere scatter sunlight and blue light is scattered more strongly than red light. (It’s the same Faraday-Tyndall effect observed when shining light through Faraday’s gold colloids.)
James Dewar in the Royal Institution, circa 1900
Public domain
A Dewar flask
Royal Institution
The x-ray spectrometer developed by William Henry Bragg.
Royal Institution
Bragg’s rock salt model
On Christmas Day, 1892, James Dewar exhibited his newly invented Dewar flask at the Royal Institution for the first time, which he used for his cryogenic experiments on liquefying gases. Back in 1872, Dewar and Peter Tait had built a vacuum-insulated vessel to keep things warm, and Dewar adapted that design for his flask, designed to keep things cold—specifically cold enough to maintain the extremely low temperatures at which gases transitioned into liquid form. Dewar failed to patent his invention, however; the patent eventually went to the Thermos company in 1904, which rebranded the product to keep liquids hot as well as cold.
As for William Henry Bragg, he studied alpha, beta, and gamma rays early in his career and hypothesized that both gamma rays and x-rays had particle-like properties. This was bolstered by Max Von Laue‘s Nobel Prize-winning discovery that crystals could diffract x-rays. Bragg and his son, William Lawrence—then a student at Trinity College Cambridge—began conducting their own experiments. Bragg pere invented a special “ionization spectrometer,” in which a crystal could be rotated to precise angles so that the different scattering patterns of x-rays could be measured. The pair used the instrument to determine the structure of crystals and molecules, winning the 1915 Nobel Prize in Physics for their efforts. That spectrometer, the prototype of today’s x-ray diffractometers, is still housed in the Royal Institution, as well as their model of the atomic structure of rock salt.
Enlarge/Great British Bake Off judges Paul Hollywood and Prue Leith (top) and presenters Alison Hammond and Noel Fielding.
Mark Bourdillon/Love Productions/Channel 4
The Great British Bake Off (TGBBO)—aka The Great British Baking Show in the US and Canada—features amateur bakers competing each week in a series of baking challenges, culminating in a single winner. The recipes include all manner of deliciously decadent concoctions, including the occasional Christmas dessert. But many of the show’s Christmas recipes might not be as bad for your health as one might think, according to a new paper published in the annual Christmas issue of the British Medical Journal, traditionally devoted to more light-hearted scientific papers.
TGBBO made its broadcast debut in 2010 on the BBC, and its popularity grew quickly and spread across the Atlantic. The show was inspired by the traditional baking competitions at English village fetes (see any British cozy murder mystery for reference). Now entering its 15th season, the current judges are Paul Hollywood and Prue Leith, with Noel Fielding and Alison Hammond serving as hosts/presenters, providing (occasionally off-color) commentary. Each week features a theme and three challenges: a signature bake, a technical challenge, and a show-stopper bake.
The four co-authors of the new BMJ study—Joshua Wallach of Emory University and Yale University’s Anant Gautam, Reshma Ramachandran, and Joseph Ross—are avid fans of TGBBO, which they declare to be “the greatest television baking competition of all time.” They are also fans of desserts in general, noting that in medieval England, the Catholic Church once issued a decree requiring Christmas pudding four weeks before Christmas. Those puddings were more stew-like, containing things like prunes, raisins, carrots, nuts, spices, grains, eggs, beef, and mutton. Hence, those puddings were arguably more “healthy” than the modern take on desserts, which contain a lot more butter and sugar in particular.
But Wallach et al. wondered whether even today’s desserts might be healthier than popularly assumed and undertook an extensive review of the existing scientific literature for their own “umbrella review.” It’s actually pretty challenging to establish direct causal links in the field of nutrition, whether we’re talking about observational studies or systemic reviews and meta-analyses. For instance, many of the former focus on individual ingredients and do not take into account the effects of overall diet and lifestyle. They also may rely on self-reporting by study participants. “Are we really going to accurately report how much Christmas desserts we frantically ate in the middle of the night, after everyone else went to bed?” the authors wrote. Systemic reviews are prone to their own weaknesses and biases.
“But bah humbug, it is Christmas and we are done being study design Scrooges,” the authors wrote, tongues tucked firmly in cheeks. “We have taken this opportunity to ignore the flaws of observational nutrition research and conduct a study that allows us to feel morally superior when we happen to enjoy eating the Christmas dessert ingredients in question (eg, chocolate). Overall, we hoped to provide evidence that we need to have Christmas dessert and eat it too, or at least evidence that will inform our collective gluttony or guilt this Christmas.”
The team scoured the TGBBO website and picked 48 dessert recipes for Christmas cakes, cookies, pastries, and puddings, such as Val’s Black Forest Yule Log, or Ruby’s Boozy Chai, Cherry and Chocolate Panettones. There were 178 unique ingredients contained in those recipes, and the authors classified those into 17 overarching ingredient groups: baking soda, powder and similar ingredients; chocolate; cheese and yogurt; coffee; eggs; butter; food coloring, flavors and extracts; fruit; milk; nuts; peanuts or peanut butter; refined flour; salt; spices; sugar; and vegetable fat.
Wallach et al. identified 46 review articles pertaining to health and nutrition regarding those classes of ingredients for their analysis. That yielded 363 associations between the ingredients and risk of death or disease, although only 149 were statistically significant. Of those 149 associations, 110 (74 percent) reduced health risks while 39 (26 percent) increased risks. The most common ingredients associated with reduced risk are fruits, coffee, and nuts, while alcohol and sugar were the most common ingredients associated with increased risk.
Take Prue Leith’s signature chocolate Yule log, for example, which is “subtly laced with Irish cream liqueur.” Most of the harmful ingredient associations were for the alcohol content, which various studies have shown to increase risk of liver cancer, gastric cancer, colon cancer, gout, and atrial fibrillation. While alcohol can evaporate during cooking or baking, in this case it’s the cream filling that contains the alcohol, which is not reduced by baking. (Leith has often expressed her preference for “boozy bakes” on the show.)
By contrast, Rav’s Frozen Fantasy Cake contains several healthy ingredients, most notably almonds and passion fruit, and thus carried a significant decreased risk for disease or death. Ditto for Paul Hollywood’s Stollen, which contains almonds, milk, and various dried fruits. “Overall, without the eggs, butter, and sugar, this dessert is essentially a fruit salad with nuts,” the authors wrote. That is, of course, a significant caveat, because the eggs, butter, and sugar kinda make the dessert. But Wallach et al. note that most of the dietary studies condemning sugar focused on the nutritional effects of sugar-sweetened beverages, and none of TGBBO Christmas dessert recipes used such beverages, “no doubt because they would have resulted in bakes with a soggy bottom.”
The BMJ study has its limitations, relying as it does on evidence from prior observational studies. Wallach et al. also did not take into account how much of each ingredient was used in any given recipe. Regardless of whether the recipe called for a single berry or an entire cup of berries, that ingredient was weighted the same in terms of its protective effects countering the presumed adverse effects of butter. Would a weighted analysis have been more accurate? Sure, but it would also have been much less fun.
So, is this a genuine Christmas miracle or an amusing academic exercise in creative rationalization? Maybe we shouldn’t overthink it. “It is Christmas so just enjoy your desserts in moderation,” the authors concluded.
