Perfect cacio e pepe? Physicists experiment in search of the ideal recipe

Few things impress dinner guests as much as a freshly prepared, perfectly prepared pasta dish.

As a passionate cook born in Rome , I believe that cacio e pepe — a typical Roman recipe, simple and delicious, but full of pitfalls — is a bold choice for those who are just starting to cook.

But the recipe is simple: pasta , cheese (cacio) and pepper (pepe). That's it.

“When you’re working with just pasta, Pecorino Romano cheese and black pepper, there’s no room for error,” explained Michele Casadei Massari , chef and CEO of Lucciola restaurant in Manhattan, in an email interview with CNN International.

“The biggest challenge is creating a stable emulsion: if the cheese gets too hot or the water-to-starch ratio is wrong, the sauce will fall apart,” he said.

When this happens, the cheese turns into a lumpy paste that sticks to everything — except the pasta, which is left there, abandoned and tasteless.

How can you avoid this culinary disaster? With a lot of practice — making mistakes along the way, as I have done — or with the help of science.

Eight Italian physicists have teamed up to unlock the secret to the perfect cacio e pepe. They studied how cheese, starch and water behave at different temperatures to make the recipe foolproof. The study was published on April 29 in the journal Physics of Fluids.

The trick? Add a precise amount of cornstarch relative to the total weight of the cheese, just enough to avoid the dreaded lumps.

I confess that, when I heard about this technique, my purist side of Roman cuisine was a little hesitant.

The science behind the dish

In a conversation in Italian, three of the authors explained that the idea came after a few failed attempts to prepare large batches of cacio e pepe. Since they were all already familiar with the concept of phase separation in liquids, they decided to investigate the problem scientifically.

“We all spent time at the Max Planck Institute in Dresden, Germany — some as PhD students, some as postdocs,” said Daniel Maria Busiello, a statistical physicist at the University of Padua. “We often cooked Italian food, for Italians and non-Italians alike.”

Making large batches of cacio e pepe, however, was nearly impossible. “It was hard to control the temperature of the pasta and sauce, and lumps would form,” Busiello recalls.

“There was one time when it was inedible. That’s when something clicked in our heads,” said Ivan Di Terlizzi, another author and one of the best cooks in the group.

He shared his theory with Giacomo Bartolucci , now a biophysicist at the University of Barcelona. Bartolucci had studied how proteins separate and aggregate in cells — and saw similarities to the behavior of cheese in the recipe.

“We started from a practical problem and a theoretical hypothesis,” explained Busiello.

Revolutionizing Italian cuisine is dangerous

Tampering with a traditional Italian recipe, even with scientific evidence, is a delicate matter. That’s why all the authors of the study are Italian — on purpose. “If we have to piss someone off, let it be Italians pissing other Italians,” Di Terlizzi joked.

To understand what happens to the sauce under heat, they recreated the recipe in the laboratory, with strict temperature control.

“We made small portions with exact amounts of cheese, starch and water, and heated everything gradually with a sous vide device,” explained Di Terlizzi.

At each stage, they collected samples of the sauce, placed them in petri dishes and photographed them from above, observing how and when the clumps formed.

The danger of the “mozzarella phase”

The starch concentration in the sauce has proven to be crucial to maintaining the stability of the emulsion. If the starch is less than 1% of the weight of the cheese, the risk is falling into the so-called “mozzarella phase” — when the sauce clumps even at lower temperatures. With 2% to 3% starch, the result is ideal.

In the recipe tested for two people, they used 5g of starch (corn or potato) dissolved in water and heated until it turned into a gel. Then, this mixture was cooled and combined with 200g of cheese.

Using sodium citrate, a common additive in commercial sauces like mac & cheese, also worked, but left a slight artificial taste, according to Di Terlizzi.

The sauce obtained with the scientific recipe is much more stable — it can withstand temperature variations and can even be reheated.

The secret, once again, lies in the emulsion process. If the cheese is combined with the starch at low temperatures, the structure remains firm. If it is done when the cheese is already too hot, the proteins become disorganized and become a mess.

I’ve seen many “foolproof tips” for making carbonara, for example, that include adding cream — a sacrilege. But for the sake of science (and curiosity), I decided to test the recipe and talk to the researchers behind the study.

Testing the scientific recipe

I tested the recipe. The step-by-step instructions were simple, it just required more steps than I'm used to (like making the starch gel).

It was strange working with such a smooth cream cheese — it almost looked like a ready-made sauce from the supermarket. The pepper is still the same: just grind it freshly and toast it in the pan to release its aroma.

My husband and I loved it. The flavor was great, and the fact that the sauce doesn't require much attention on the stove helps a lot, especially when it comes to the mantecatura (the final mixture with the pasta).

If I felt any difference, it was in the texture. Knowing that there was starch in there influenced my perception. My husband didn't even notice.

As a home cook and proud Roman, I know my quest for the perfect old-fashioned cacio e pepe will continue for a lifetime. But this scientific version has pleasantly surprised me—and it might just be the push you need for those who’ve always been afraid to try it.

Chefs' tips for the traditional dish

But what exactly makes it so challenging to prepare the dish the traditional way — that is, emulsifying the cheese with the pasta cooking water?

It's virtually impossible to know exactly how much starch is in the cooking water, so the success of the emulsion is something of a gamble. However, there are tricks that can help you avoid disaster.

One of them, suggested by Massari, is to use less water to cook the pasta .

“For cacio e pepe, I recommend using about 1.5 to 2 liters of water for every 200 g of pasta — that is, a ratio of around 1 part pasta to 6 or 7 parts water by weight, much lower than the traditional ratio,” said the chef.

A classic rule for cooking pasta, according to Massari, is to use about 1 liter of water for every 100 g of pasta, with 2 teaspoons of salt.

The researchers, who arbitrarily used a 10-to-1 ratio (water/pasta), found that reducing this volume by two-thirds concentrated the pasta's natural starch to a safe level.

Massari also recommends emulsifying the cheese with the pasta water at less than 60°C, which is in line with the new study's findings on temperature.

“First I make a cold cream with cheese, using finely grated Pecorino and a small amount of the starchy cooking water, beating until smooth. Then I mix this base with the pasta already off the heat and freshly ground black pepper, adjusting the texture with more water, if necessary,” he explained.

“The result should be a silky, even sauce that coats each strand of pasta — not a broken or heavy mixture.”

“The natural starch in pasta, when used well, is more than enough to create a creamy, stable and authentic sauce, without compromising the nutritional value of the dish,” he added.

Another chef's trick to save time when following the traditional method is the so-called “pasta regeneration” — which consists of cooking the pasta for about 70% of the indicated time, cooling it quickly in ice water to stop the gelatinization and finishing it later, just before serving.

“This method preserves the al dente texture and also increases the final release of starch on the surface, which is essential for stabilizing delicate emulsions,” explained Massari.

Celebrating with the tested recipe

Researchers say the scientifically optimized recipe has become a meme, both online and offline.

“Some users on social media were quite critical of the recipe we proposed, even though it has been used before in prestigious restaurants,” Di Terlizzi told CNN International. “But overall, I can say that enthusiasm prevailed, especially among scientists.”

“We’re not going to say we’ve invented the definitive method,” he said. “But this method keeps you from ruining a good, expensive, hard-to-find pecorino cheese.”

And for the researchers, it’s personal: “We’re in Germany. We have to import pecorino from Italy. You can’t just buy it at the store every day,” Di Terlizzi said. “So when the dish turns out wrong, it’s annoying.”

The publication of the study was celebrated with a huge pasta dinner — the researchers prepared more than 1.8 kilograms for the guests.

“We were super nervous because everyone there knew about the experiment — but it all worked out,” Busiello said. Bartolucci added: “It was our acid test.”

Scientifically optimized Cacio e Pepe recipe

Editor's note: CNN International's summary of the recipe presented in the study. Pecorino Romano DOP (Protected Designation of Origin) and tonnarelli pasta can be found in Italian grocers or online specialty stores.

Serves 2 people

Ingredients

• Salt
• 5 g (2 teaspoons) cracked black peppercorns, plus more for serving
• 5 g (2 teaspoons) cornstarch or potato starch
• 200 g (1 ½ cups tightly packed) grated Pecorino Romano DOP
• 300 g (10.6 oz) pasta, preferably *tonnarelli* (spaghetti or rigatoni also work)

Instructions

1. Bring a large pot of lightly salted water to a boil;
2. Meanwhile, toast the peppercorns in a dry skillet over low heat until aromatic, 1 to 2 minutes. Remove from heat immediately;
3. Prepare the starch gel: dissolve the starch in 50 g (about 3 tablespoons + 1 teaspoon) of cold water, stirring with a whisk. Bring to a boil over low heat until thickened and almost translucent. Remove from heat and stir in 100 g (about 6 ¾ tablespoons) of water to cool. The mixture will return to a liquid state;
4. Make the cream cheese: place the water with starch, grated cheese and pepper in the food processor and beat until it forms a smooth cream;
5. Cook the pasta until *al dente*, according to the package instructions. Reserve 1 cup (237 ml) of the cooking water before draining;
6. Mix the pasta with the sauce, stirring well. Adjust the texture with more water if necessary. The sauce should be slightly runny, as it thickens as it cools. If necessary, it can be gently reheated (to 80–90 °C) before serving;
7. Finish with more grated cheese and pepper and serve immediately.

Cacio e Pepe by chef Michele Casadei Massari

“I recommend using high-quality spaghetti made with durum wheat semolina, extruded in bronze and slowly dried at low temperatures,” says the chef. “I prefer Matt wheat, an ancient variety grown mainly in Puglia and Sicily.”

You can find Matt's spaghettoni, Sarawak black pepper and Pecorino Romano DOP in specialized online stores.

Serves 2 people

Ingredients

* Sea salt, preferably coarse and Sicilian * 5g (1 tsp) freshly ground Sarawak black pepper, plus more for serving * 100 g (1 tightly packed cup) grated Pecorino Romano DOP, plus a little more for serving

* 200 g (7 oz) of *spaghettoni*, preferably Matt wheat