Cacio e Pepe – literally cheese and pepper – is a pasta dish from the Lazio region of central Italy that consists of just Pecorino Romano cheese, black pepper, tonnarelli pasta and water. And it is a fabulously smooth, creamy dish.
Yet every Italian chef knows this simplicity is deceptive. Get the proportions of ingredients wrong and Cacio e Pepe quickly becomes a soggy, lumpy mess. Perfecting the dish is surprisingly tricky, but how come?
Now we get an answer thanks to the work of Giacomo Bartolucci at the University of Barcelona and colleagues who have explored the complex behavior of the emulsion that forms when pecorino cheese is added to water used to cook pasta, which is filled with starch. It turns out that the proportion of cheese, the amount of starch in the water and the temperature must all be carefully controlled to achieve the perfect result.
Perfect Pasta
Bartolucci and co say that through careful experimentation, they have finally determined the perfect conditions. “We present a scientifically optimized recipe based on our findings, enabling a consistently flawless execution of this classic dish,” they say.
Food scientists have long been both fascinated and puzzled by the complex behaviors of edible foams and emulsions such as mayonnaise, ice cream.
A typical recipe for Cacio e Pepe is simple. Cook the tonnarelli — a spaghetti-like pasta — in boiling, salted water until it is al dente, soft but chewy. Set aside a cup of this pasta water and slowly add it, while stirring, to a large bowl of the grated Pecorino cheese and black pepper. Finally, add the pasta allowing the creamy mixture to entirely coat it and serve hot. Ecco qui!
Don’t be surprised, however, if your delicious creamy sauce separates into a revolting lumpy paste. What this recipe fails to explain is that the cheese will separate and form into clumps under a wide range of seemingly ordinary conditions.
Cheese is a complex colloidal system, composed of proteins, fats, and water. When Pecorino Romano is mixed with hot water, the proteins must remain finely dispersed to create a smooth emulsion. If they aggregate, they form clumps, ruining the texture of the sauce.
Temperature plays a crucial role in this process. If the cheese is added to water that is too hot, its proteins denature and coalesce into large, rubbery clumps.
To find the perfect conditions, Bartolucci and co systematically measured the effects of changes in starch concentration, cheese-to-water ratio, and temperature. They heated mixtures under controlled conditions, capturing images of the resulting emulsions at different temperatures. By quantifying the size and distribution of protein aggregates, they constructed a phase diagram illustrating the boundaries between smooth sauce and clumpy separation.
The results will be hugely useful for any chef or would-be food scientist. They confirm, for example, that cheese added to water alone forms system-wide clumps at around 65°C, resulting in a phase-separated sauce.
The starch in pasta water is a key stabilizing agent. Starch molecules interact with cheese proteins, helping to prevent their aggregation. Bartolucci and co found a critical starch concentration: when starch is less than 1 per cent of the cheese mass, clumping occurs readily.
Higher starch levels lead to improved emulsification but up to a maximum of about 4 per cent. Higher concentrations tend to make the water gloopy and unappetizing. Increasing starch concentration also shifts the phase boundary, allowing the sauce to remain stable at higher temperatures.
They also found that the optimal cheese-to-water ratio is close to 1:1 by mass, with deviations in either direction leading to increased phase separation.
Roman Tips
Based on their findings, Bartolucci and co propose a set of scientific tips for would-be Cacio e Pepe chefs:
Cheese-to-Water Ratio: the optimal emulsification occurs with a 1:1 ratio by mass of finely grated Pecorino Romano and hot pasta water.
Starch: Standard pasta water may not contain enough starch to prevent clumping. Instead, dissolve 4 grams of cornstarch in 40 grams of water, and heat it until it becomes clear.
Temperature: Allow the pasta water to cool slightly before mixing with cheese — a target of 55-60°C prevents premature protein aggregation.
Blend: Instead of manually stirring, use a hand blender to ensure fine dispersion of cheese particles in the starch-enriched water.
Adjust: If the sauce is too thick, add more warm pasta water gradually to reach the desired smoothness.
Cacio e Pepe is a staple dish in many Roman restaurants, but it was originally a high-calorie meal that shepherds prepared for themselves. The pasta, pepper and Pecorino cheese are all dry ingredients that can be easily packed into a saddle bag for long journeys. They and their families surely knew exactly how to make their sauce creamy and delicious.
“A true Italian grandmother or a skilled home chef from Rome would never need a scientific recipe for Cacio and Pepe, relying instead on instinct and years of experience,” say Bartolucci and co. “For everyone else, this guide offers a practical way to master the dish.”
Enjoy!
Ref: Phase Behavior of Cacio and Pepe Sauce: arxiv.org/abs/2501.00536
