At first glance, Cacio e pepe looks easy. Just three ingredients — pasta, Pecorino Romano, and black pepper — and you get a delicious staple cherished by generations. But if you’ve ever tried to make it without instructions, the odds are you ended up with stringy clumps instead of a silky sauce.

Fret not; physics has the answers.

A team of physicists, mostly Italian and living abroad, embarked on an unusual mission: to understand why this deceptively simple dish so often fails — and how to prevent it. Their findings, recently published in Physics of Fluids, reveal the science behind the mozzarella-like blobs that plague bad Cacio e pepe, and propose a precise fix: just the right amount of starch, added in a new way.

Pasta physics

Cheese and water don’t usually like each other. “When heated, cheese proteins change their configuration and, therefore, aggregate,” explained Dr. Daniel Busiello, a co-author from the Max Planck Institute for the Physics of Complex Systems.

In culinary terms, that means the Pecorino clumps. You’d expect it to melt evenly into a creamy sauce, but instead, it breaks apart into greasy pools and chewy blobs — a failure that’s sometimes called “the mozzarella phase”. But when mixed with the right amount of starch, the proteins don’t clump. The starch coats the proteins, reducing their interaction and allowing the sauce to stay smooth.

That’s not just kitchen lore. It’s physics.

To test the idea, the scientists cooked and photographed dozens of mixtures of cheese, water, and different concentrations of starch. Each sample was gently heated in a sous-vide bath, cooled, and observed. Using image analysis techniques, they created a phase diagram — a visual map showing when the sauce turned smooth and when it devolved into clumps.

Phase diagrams show how substances behave under different conditions like temperature and concentration. This helps scientists predict whether different objects like sauces, rocks, or even neutron stars will behave.

According to this phase diagram, anything below 1% starch (relative to cheese weight) will lead to the dreaded mozzarella phase. Meanwhile, on the flip side, the sauce turns stiff and unappetizing at 4%. The sweet spot lies between 2% and 3%.

Precision cooking

The scientists aren’t trying to replace intuition. “A true Italian grandmother or a skilled home chef from Rome would never need a scientific recipe for Cacio e pepe,” they wrote. “For everyone else, this guide offers a practical way to master the dish.”

The researchers also give a practical example. Let’s say you want to make Cacio e pepe for two hungry people. You’d use 300 g of pasta (tonnarelli is preferred, though spaghetti or rigatoni also works well) and 200 g of cheese.

“The amount of cheese can, of course, vary depending on personal taste. Traditionalists would insist on using only Pecorino Romano DOP, but some argue that up to 30% Parmigiano Reggiano DOP is acceptable, though this remains a point of debate,” the researchers add.

For two people, the team suggests the following science-based recipe for Cacio e pepe:

• 200g of Pecorino Romano
• 5g of corn or potato starch, dissolved in 50g of water and gently heated until gelatinized
• Add 100g more water to cool the mixture before adding the cheese
• Blend until smooth, then mix with 300g of al dente pasta
• Add freshly toasted black pepper at the end

Do this, and you should end up with a velvety sauce that clings evenly, resists clumping — even when reheated — and is scientifically foolproof.

The idea isn’t just about controlling the starch. It’s about taming the complex interactions inside the sauce. When the team fixed the starch level and varied the cheese-to-water ratio, they discovered a binodal curve — a boundary between smooth and clumpy states — strikingly similar to other phase transitions in physics and chemistry.

In fact, they developed a minimalist thermodynamic model based on casein and whey proteins to replicate the behavior, capturing how denatured whey proteins aggregate at higher temperatures and form networks.

Starch? Eww

Many Italian traditionalists may have felt a cold shiver at the thought of adding starch in the pasta.

The team tried another solution: trisodium citrate. This substance is commonly used in processed cheese as an industrial-grade stabilizer. It works like a charm — but there’s a catch.

At concentrations of 2% or more (relative to cheese mass), trisodium citrate prevents clumping entirely. But it also blunts the cheese’s sharp flavor. “The sauce stabilization is more efficient,” the researchers write, “but we found the taste of the cheese to be slightly blunted, likely due to the basic properties of the salt.”

So, the starch method remains the best compromise between science and soul. It respects the ingredients — and the dish’s origins. If you don’t have confidence in your cooking skills or are not a “true Italian grandmother,” that’s probably the way to go.

The paper may sound whimsical, and let’s face it: it is. But there’s growing interest in culinary physics, where researchers treat recipes like scientific problems. Earlier studies explored why dry spaghetti never breaks cleanly in two, how pasta softens and curls in boiling water, and how to tell when it’s perfectly cooked using a ruler.

And the project isn’t over.

Next on the team’s menu: pasta alla gricia. It’s similar to Cacio e pepe but adds cured pork cheek — guanciale — and, according to Dr. Busiello, is mysteriously easier to get right. “We don’t know exactly why. This is one idea we might explore in the future.”

The article “Phase behavior of cacio e pepe sauce” is authored by Giacomo Bartolucci, Daniel Maria Busiello, Matteo Ciarchi, Alberto Corticelli, Ivan Di Terlizzi, Fabrizio Olmeda, Davide Revignas, and Vincenzo Maria Schimmenti. The study was published in Physics of Fluids