The Optimal Time to Dunk an Oreo, According to Science

iStock // Lucy Quintanilla
iStock // Lucy Quintanilla

Have you submerged an Oreo into a glass of milk and lingered too long? Did you watch in horror as America's supposedly favorite cookie disintegrated before your very eyes? Fear no more! Here's how to find (and elongate) your optimal dunk time.

THE SHORT ANSWER

Dip your cookie for three seconds, give or take. Carry on with your life, dear reader.

THE LONG ANSWER

Well, it depends. Do you prefer a crispy cookie masked in a thin veneer of milk? A cookie that has metamorphosed into unrecognizable gloop? Do you believe in a Goldilocks zone, a Platonic middle-ground that’s neither too dry, nor too spongy, but just right? It’s all subjective. But let’s assume you want an Oreo that is pleasantly soggy and has maintained its structural dignity.

There’s math for that. In the late 1990s, Len Fisher, then a professor of physics at the University of Bristol, sparked a media storm when he argued that a decades-old mathematical formula could predict the perfect dunk time for a cookie. It’s all thanks, he claimed, to capillary action.

Water molecules are adhesive: They cling to solid surfaces. (It’s why water in a beaker shows a meniscus—it’s attracted to the sides of the container.) When water enters a small tube, the liquid can adhere to surfaces in ways that seem to defy gravity: This is why water may crawl up your drink’s straw and why a paintbrush seems to slurp up liquid. That’s capillary action in a nutshell.

On a microscale, a cookie is essentially a series of small, starchy tubes. Fisher writes in his book How to Dunk a Doughnut that a dunking liquid (in our case, milk) is “held in place in the porous matrix by the pressure across the meniscus in the smallest of pores.” In other words, capillary action helps the milk spread through the cookie. In the early 20th century, the American scientist E.W. Washburn cooked up a formula to describe this watery journey.

Washburn's Equation
Lucy Quintanilla

Washburn tested and confirmed his formula by observing ink blots spread through paper. (A simplified version of his equation explains how inkjet printers spit out dry, sharp-looking text.) But it took nearly a century for someone such as Fisher to apply the formula to baked goods: After finding reliable numbers for the variables, Fisher rearranged the equation and solved for T (time).

He discovered that the perfect dipping time for a typical British dunking biscuit with a conventional dip was three-and-a-half to five seconds.

But Fisher never tested Oreos. So in 2016, members of Utah State University’s Splash Lab—an academic group studying the behaviors of fluids—put Oreos to the test. (Splash Lab, we should note, has an appetite for quirky experiments: They’ve studied the fluid dynamics of urinal splashback, analyzed the physics of the perfect skipping stone, and even tested the insulating properties of beards.)

Three researchers gathered Oreos, Chips Ahoy, Nutter Butter, and Graham Crackers and dipped the cookies halfway in 2 percent milk for half a second to seven seconds. After dunking, the team weighed the treats and measured how much milk had been absorbed.

The results: Oreos absorbed 50 percent of their potential liquid weight in just one second. After two seconds, they absorbed 80 percent. The number flatlined briefly for a second. After the fourth second, the cookie maxed out: It absorbed all its possible milk. “This data indicates that for the tested cookies, keeping your cookie in the glass any longer than five seconds does not lead to any additional milk entering the cookies,” their study suggested.

A graph of optimal cookie dunk times.
Oreo cookies absorbed milk at the same rate as Nutter Butter, taking in 100 percent of their liquid weight in four seconds.
Splash Lab

Splash Lab then performed a second test, dunking all cookies for six seconds and attaching them horizontally to a clamp. They waited for the cookies to collapse. The Oreo lasted an impressive five minutes! Compare that to measly Graham Crackers, which crumbled after eight seconds.

The takeaway: Three seconds is enough time to saturate most of an Oreo. There’s no benefit to dunking longer than four seconds. (Unless you want to watch the cookie crumble into your milk. As Splash Lab’s Randy Hurd, a mechanical engineering Ph.D. candidate, told us: “Waiting for the crisp cookie structure to break down is not necessarily a waste of time if that’s what you prefer.” We don’t judge.)

However, things get more complicated if you choose a different kind of dairy.

THE LONGER ANSWER

Your choice of milk could change the optimal dunk time by a few split seconds.

In 2011, researchers published a study in the Journal of Food Science that explained why milk doesn’t immediately turn breakfast cereal into mush: Fats and other solids in the dairy hindered “liquid infiltration,” slowing absorption. The same process is true of cookies, says Jennifer Fideler, a graduate student in food science at North Carolina State University.

Milk, for one, is full of sugars. Sugars are hygroscopic, meaning they hold onto moisture and can prevent liquid from seeping into the cookie. Additionally, fat and carbohydrate molecules are big. They can prevent the water in the milk from infiltrating the cookie’s porous matrix.  “Not only is it likely that the fat content of the milk (whole, 2 percent, skim, even heavy whip!) would affect the rate of moisture migration ... but the fat included in the cookie—and even moreso the cream filling—would help resist the influx of fluid,” Fideler wrote in an email.

Fat content doesn’t just slow down absorption time. It’s also known to enhance the flavor. In 1999, Len Fisher tested more than 200 British biscuit and drink combinations and concluded that milk could make a cookie 11 times more flavorful. (This wasn’t peer-reviewed, and it was sponsored by a biscuit company, so take it for what it’s worth.) “Milk is essentially fat droplets suspended in water and those fat droplets stay around in your mouth and they hang on to the flavour in the biscuit so that the aroma can be released up to the back of your nose,” Fisher told the BBC.

So, if you’re the type of person who dreams of extending the optimal Oreo dunk time while enhancing the flavor, toss the skim milk down the drain and pour a cup of high-fat dairy. Whole milk (3.25 percent butterfat) spiked with half-and-half (generally 10 percent butterfat) could extend your dunk time. But if you wanted to indulge and throw a Hail Mary—and have a few spare notches left in your belt—try dunking in heavy cream (36 percent butterfat). Heck, while we’re at it, why not go all the way and dip it in melted butter (80 percent butterfat).

(We’d like to take this moment to say we are not licensed to give nutritional advice and are not liable for culinary crimes against humanity. So maybe don't do this.)

THE MUCH LONGER ANSWER

If you wanted to boost the optimal Oreo dunk time even longer, there’s another principle you can hack: Water Activity.

Water activity is a measurement of how likely something gives away moisture. It’s measured on a scale from 0 to 1: Milk, for example, possesses a high water activity of 0.98. It readily gives its water away. A cookie, on the other hand, has a water activity hovering around 0.3. It holds onto its moisture and is more likely to absorb water.

Food manufacturers and processors have to constantly contend with water activity. It’s critical in determining a product’s safety, stability, and shelf life: Controlling water activity is the easiest way to prevent—and predict—the spread of dangerous bacteria [PDF]. (That’s because items with a high water activity are more likely to give water away to nasty microorganisms, causing spoilage.)

But for our selfishly sweet-toothed purposes today, water activity is just another factor affecting the critical cookie dipping time. A liquid with a lower water activity will hold onto its moisture more tightly than standard milk, Fideler explains. So, if you wanted to extend the optimal dunk time further, you should try to dip your Oreo into dairy that not only contains lots of fats and carbs, but also possesses a relatively low water activity. With that in mind, we have the perfect recommendation: Sweetened condensed milk. (We don’t actually recommend this.)

Boasting a high butterfat content (8 percent), obscene loads of carbs (166 grams per cup), and a relatively low water activity (.87), sweetened condensed milk is perfect if you’re the kind of person who relishes long dunk times and believes “calories” are just another government conspiracy designed to scare you from chugging modernity’s decadent ambrosias.

Dunk away!

This story originally ran in 2017.

3 Cold Coffee Treats To Beat The Heat

Mental Floss Video
Mental Floss Video

Loving coffee is a year-round activity, but in the dog days of summer you may not be in the mood for a steaming hot cup of joe. That’s why we asked Eamon Rockey, Director of Beverage Studies at the Institute of Culinary Education, to help us concoct three delicious cold coffee treats.

Coffee tonic is a simple, refreshing alternative when you get sick of plain old iced coffee. Granita di caffè—basically a grown-up snow cone— is an Italian classic. And Eamon’s “milk and honey” take on a Greek frappè is a caffeinated milkshake with just enough sweetness to be addictive.

The recipes all start with cold brew concentrates, which are increasingly available at grocery stores and ensure a consistent product from start to finish. You could also use refrigerated coffee leftover from the morning or any other (preferably strong) iced coffee; you may sacrifice a bit of consistency and flavor, but something tells us they’ll still be delicious.

Coffee Tonic Recipe

Ingredients:

Grady’s Cold Brew Concentrate (or your preferred substitute)
Tonic Water
Ice
Lemon Peel

Instructions:

  1. Pour equal amounts of cold brew concentrate and tonic water into glass.
  2. Add ice and stir.
  3. “Express” (i.e. squeeze to release essential oils) a large piece of lemon peel into glass
  4. Garnish with lemon and serve.

Granita Di Caffè Recipe

Ingredients:

Red Thread Cold Brew Concentrate With a Hint of Chocolate (or your preferred substitute)
Simple Syrup (Optional)
Berries and/or Whipped Cream to Garnish

Instructions:

  1. Pour cold brew concentrate into a freezer safe vessel
  2. Optionally, for a sweeter treat, add ¼ cup simple syrup (50 percent water, 50 percent sugar) and stir
  3. Place into a freezer and let nearly freeze (1-2 hours)
  4. Break up any ice crystals with a fork and place back in freezer for roughly 30 minutes
  5. Repeat step four two or more times, as needed, until the mixture is all icy granules
  6. Alternately, skip steps three to six and leave coffee mixture until frozen (2-3 hours). Scrape vigorously with a fork. You may sacrifice some of the light texture of the other method, but the process is considerably simpler.
  7. Serve with berries or (ideally fresh) whipped cream

“Milk and Honey” Greek Frappè Recipe

Ingredients:

One Half of a Vanilla Bean
3 Tbsp. Heavy Cream
3 Tbsp. Honey
3 Tbsp. Milk
4 oz. Grady’s Cold Brew Concentrate (or your preferred substitute)
Splash of soda water (optional)
Ice

Instructions:

  1. Scrape half of a vanilla bean and add to heavy cream
  2. Make whipped cream by mixing with whisk/hand mixer, or by shaking vigorously in cocktail shaker
  3. Add honey to milk and stir to combine
  4. Add milk/honey mixture to whipped cream and stir
  5. Pour cold brew concentrate and a splash of soda water into glass
  6. Add ice
  7. Top with half of the whipped cream/milk/honey mixture and stir
  8. Garnish with the leftover vanilla bean pod 

14 Freshly-Brewed Facts About Starbucks

Starbucks
Starbucks

When Howard Schultz visited Milan, Italy in 1983 and realized the city was home to more than 1500 coffee bars, a light bulb went off in his head. Four years later, the ambitious Schultz acquired Starbucks—which had previously only sold ground coffee in bags, with no single servings—and proceeded to turn it from a six-store Seattle operation into a global phenomenon. Unlock the secrets of your home away from home with these 14 frothy facts.

1. Starbucks has a ban on smells.

Because aroma is so crucial to the Starbucks experience, Schultz—the company's longtime CEO who retired in 2018 and is now its Chairman Emeritus—laid down the law early on: Nothing can interfere with the smell of their freshly-ground coffee. The stores banned smoking in the late 1980s, years before the practice was commonplace; employees are alsao asked not to wear perfume or cologne [PDF].

2. The Starbucks mermaid used to show nipple.


Jim Forest, Flickr // CC BY NC-ND-2.0

The siren of the famous Starbucks logo is intended to represent the seductive power of coffee, with her hair tastefully covering any hint of immodesty. But when Starbucks was still a regional chain in 1970s Seattle, their logo was far more candid: The mermaid had fully-exposed breasts. Some customers commented on it, but it didn’t become scandalous until the company began making deliveries and had to put their signage on trucks. Reluctant to traffic in portable nudity, the logo was revised.

3. An immunologist cracked the Starbucks coffee code.

Infectious disease specialist Don Valencia was essentially just goofing off in 1990 when he developed a coffee bean extract that smelled and tasted just like the real thing. After neighbors couldn’t tell the difference between his sample and fresh coffee, he tried it out on a barista. Eventually, word got to Starbucks executives, who hired Valencia in 1993. Using his discovery to branch out into retail sales, Starbucks quickly became a top-seller of bottled coffee and super-premium ice cream—for a time, they even outsold pint-sized king Häagen-Dazs.

4. There have been Starbucks stores made out of old shipping containers.

A Starbucks store made out of a shipping container
Starbucks

In a monument to the company’s eco-friendly attitude, several stores built out of retired shipping containers have opened since 2011. Some use run-off drains to feed rainwater to nearby vegetation; others use local materials such as discarded wooden fencing to complete the job. The recycled storefronts are typically drive-thru only, but video cameras allow patrons to see a friendly barista's face. At 1000 square feet, they’re also smaller than a typical store—and Starbucks has every intention of using that tiny footprint to burrow its way into locations previously thought to be too small to lease.

5. Starbucks managers were forced to play with Mr. Potato Head.

Eager to ramp up efficiency in the face of stiffer competition in 2009, Starbucks dispatched executive Scott Heydon for some updated managerial training. To demonstrate how employees can cut down on idle time behind the counter, Heydon instructed managers to assemble a Mr. Potato Head toy and then put him back in his box in under 45 seconds. At least one supervisor was able to pick up the scattered pieces and re-assemble the spud in under 16 seconds.

6. The Starbucks CIA location is as secretive as you’d expect.

Man drinking coffee and using his laptop
hitmanphoto/iStock via Getty Images

Like most office buildings, the Central Intelligence Agency in Langley, Virginia runs on caffeine. But it doesn’t run like a typical Starbucks: Baristas undergo background checks and aren't allowed to leave their posts without a CIA escort. Customer names cannot be called out or written on cups due to security concerns. Despite the precautions, it’s still a social atmosphere: According to The Washington Post, one key member of the team that assisted in locating Osama bin Laden was recruited there.

7. The Starbucks employee dress code is very specific.

When Schultz opened his line of Il Giornale espresso bars in 1985, he mandated employees wear the bow ties and crisp white shirts common in Italy. The current dress code [PDF] has relaxed on the Pee-Wee attire but still insists on a certain kind of conformity. Rings cannot have stones; brightly-colored purple or pink hair is not welcome; untucked shirts can’t expose your midsection when bending over; ear gauges should be less than 10mm. Think you're going to sport a face tattoo or septum ring? Mister, the only thing you’re brewing is trouble.

8. California has a Starbucks ski-thru.

Skiers in Squaw Valley, California looking for a caffeine fix don’t have to take off their equipment: the Starbucks at the Gold Coast Resort is open to visitors via a Ski-Thru. They also take orders from the aerial lift. What could be better?

9. Nonfat milk resulted in a Starbucks corporate standoff.

When Howard Behar came to Starbucks as an executive in 1989, he was dismayed to find that many customers had filled out comment cards voicing their desire for nonfat milk. But Schultz and his team had decided they didn’t like the taste and that nonfat wasn’t authentically Italian. Behar argued that customers should get whatever they wanted. Store managers protested, but when Schultz personally witnessed a customer walk out over the lack of options, he relented. Today, it's estimated that half of the company’s cappuccinos and lattes are frothed without fat.

10. You can get a Butterbeer frappucCino at Starbucks (if you know the right way to ask).


RosieTulips, Flickr // CC BY NC-ND-2.0

The preferred thirst-quencher for Harry Potter fans, Butterbeer isn’t really available outside of the books or the Universal Studios attraction—but you can get a pretty good approximation by requesting a Frappucino with caramel syrup, caramel drizzle, and toffee nut syrup.

11. The round tables at Starbucks may help you feel less lonely.

Feeling self-conscious about sitting in a Starbucks by yourself? Don’t be: the round tables are there to help. The company believes that circular dining areas can make a space feel less empty when compared to the stern edges of a rectangular or square table. They don’t want you to feel alone. So, so alone.

12. The Disney Starbucks has magic chalkboards.

When Starbucks opened at Downtown Disney in Orlando, Florida, some of the company’s trademark features were tweaked to fit their magical affiliation. The chalkboard was re-imagined as a 70-inch touch screen that can render illustrations in real time. Customers can also “draw” on the screen using their fingers, take selfies, and see what visitors in Disney’s Anaheim Starbucks are up to.

13. Some Starbucks stores have the technology for the greatest cup of coffee possible.

Starbucks cares a great deal about serving an excellent cup of coffee. Employees never let brewed pots sit for more than 30 minutes, and stores use no artificially-flavored grounds. The next giant leap in bean prep might be the Clover, a proprietary machine engineered by Stanford that costs $13,000 to install and uses a vacuum and elevator system to shoot coffee grounds upward with precision water temperatures the result is said to be a peerless experience. If you’re lucky enough to be near a store that has one, expect to pay up to $5 a cup.

14. Customers think Starbucks gives away newspapers. It doesn't. Now it doesn't sell them, either.

For years, many Starbucks locations provided newspapers like The New York Times and the Wall Street Journal to customers. That practice stopped in September 2019. Why? People believed the papers were provided as a gratuity and left them in a pile or walked out with a paper without paying.

Additional Sources: Pour Your Heart Into It: How Starbucks Built a Company One Cup At a Time.

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