Food science

how-you-can-make-cold-brew-coffee-in-under-3-minutes-using-ultrasound

How you can make cold-brew coffee in under 3 minutes using ultrasound

acoustic cavitation, acoustics, bubbles, chemistry, coffee brewing, cold brew coffee, Food science, Physics, Science, sonochemistry, ultrasound / /

Save yourself a few hours —

A “sonication” time between 1 and 3 minutes is ideal to get the perfect cold brew.

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UNSW Sydney engineers developed a new way to make cold brew coffee in under three minutes without sacrificing taste.

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.

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.

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.

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The chemistry of milk washing, aka the secret to Ben Franklin’s favorite tipple

chemistry, cocktails, Food science, mixology, Science / /

Curds and whey —

Bonus: a twist on the espresso martini, with peanut butter-washed vodka, coffee, and milk curd.

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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.

Benjamin Franklin's recipe for milk punch, included in a 1763 letter to James Bowdoin.

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

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Blue cheese shows off new colors, but the taste largely remains the same

blue cheese, chemistry, food chemistry, Food science, fungus, Science / /

Am I blue? —

Future varieties could be yellow-green, reddish-brown-pink, or light blue.

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Scientists at University of the Nottingham have discovered how to create different colours of blue cheese.

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.

Color derivatives.

Enlarge / Color derivatives.

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.)

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.” height=”371″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/02/bluecheese3-640×371.jpg” width=”640″>

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.

Science of Food, 2024. DOI: 10.1038/s41538-023-00244-9  (About DOIs).

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Great British Bake Off’s festive Christmas desserts aren’t so naughty after all

baking, chemistry, cooking shows, Food science, Great British Bake Off, health, nutrition, Science / /

A Christmas miracle? —

Study: Several ingredients actually reduce rather than increase risk of death or disease.

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four smiling people at a festive picnic table munching on a tasty snack

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.

BMJ, 2023. DOI: 10.1136/bmj‑2023‑077166  (About DOIs).

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