Cacio e Pepe, what could be simpler? A traditional recipe from central Italy. It consists of noodles in a creamy blend of pecorino cheese, pepper, and starch-enriched water. But as any serious cook will tell you, a recipe with just three ingredients allows no margin for error.
“A good cacio smacks you across the face with grassy heat and a coagulated richness; it’s a universally pleasing flavor, registering in our American brains like mac and cheese Italiano.”
- Slate
For those who recognize that cooking is chemistry that you can eat, the key point in making cacio is finding a way to meld the cheese, a dairy-based fat, with a bit of water, which avoids fats at all costs, to create a creamy sauce. The mediator between the two is an emulsifier that loves both fat and water, allowing them to combine.
Lately, one emulsifying hack found in restaurants, and even offered up by noted culinary citizen scientist Kenji López-Alt, is butter. For the purist, that involves an additional ingredient that an Italian grandmother would reject out of hand. Let your heart not be troubled; physicists writing in ARXiv have studied the problem and provided a solution.
Culinary Chemistry
In cacio, the emulsifier is the pasta water, a mix of starch from the noodles and water. When adequately heated, that mixture forms a gelatin, allowing the fatty pecorino cheese and water to meld together without clumps or breaking down into puddles of water. [1] Phase separations or combinations often control a food’s texture. With time and thermodynamic equilibrium, emulsions allowing for a smoother, creamier texture can break, e.g., the ice crystal you might find in “older” ice cream, the same for the whitish discoloration on an older chocolate bar.
To create the perfect Cacio, the physicists “characterize the phase behavior of the solution containing water, starch, and cheese by systematically investigating the role of each one of these components.” More specifically, they sought a means to avoid large aggregations of cheese, which they termed the Mozzarella phase. They found that adding pasta water with its small amount of starch shed by the noodles slowed and then eliminated the Mozzarella phase (for those seeking to be more erudite, the phase transition).
“Starch thus seems to stabilize the homogeneous mixture over a large range of temperatures, allowing for less stringent temperature control during preparation. To test this hypothesis, we conducted experiments at a fixed cheese-to-water ratio while varying the starch concentration in the water and the temperature of the system.”
They found starch reduced phase separation, delayed the onset of clump formation at higher temperatures, and minimized the size of the cheese aggregates – a creamier source “less sensitive to mistakes in temperature control during preparation.” Bottom line, a creamy sauce requires a starch level of 2-3%. When the starch content is below 1% of the cheese weight, the sauce tends to separate into clumps; as starch levels rise above 4%, the sauce stiffens into a gelatinous texture as it cools.
“A true Italian grandmother or a skilled home chef from Rome would never need a scientific recipe for Cacio e Pepe, relying instead on instinct and years of experience.”
For the rest of us, the hack is to create a pasta water with the proper ratio of starch. In the following recipe, we use 160 grams of Pecorino cheese so that 4 grams of starch is optimal and accounts for the minimal amount of starch shed by the pasta as it cooks. 4 grams of cornstarch are dissolved in 40 grams of water and heated until the mixture “turns from cloudy to near clear,” a sign of gelation. This mixture is then blended with the Pecorino and pepper to create your more heat insensitive emulsion.
For two:
- Toast whole black peppercorns in a pan until fragrant, then grind them.
- Cook 240 grams of pasta, reserving some of the pasta water before draining.
- Prepare your cornstarch-Pecorino emulsifier, adding the peppercorns to taste, creating your sauce.
- Gently heat the sauce, add the drained pasta, and add reserved pasta water as you feel necessary to achieve your desired consistency.
For those who learn better by seeing rather than reading, consider this delightful YouTube video, which covers the science and cooking. Why traditional Cacio e Pepe is so hard to perfectly execute
In the end, Cacio e Pepe is proof that simplicity is an illusion in the kitchen. Whether you rely on instinct like an Italian grandmother or call on the power of physics to tame phase transitions, the perfect plate is a delicate dance of science and skill.
[1] Fun fact: the classic thickener for home chefs is often cornstarch and water mixed and then added to a hot liquid to thicken it. Physicists refer to this particular mixture as oobleck, a homage to Dr. Seuss’s 1949 Bartholomew and the Oobleck
Sources: Phase behavior of Cacio and Pepe sauce https://arxiv.org/pdf/2501.00536¶
Physicists Figure Out The Perfect Cacio E Pepe Recipe Popular Science
Slate My Cacio e Pepe Exposé
Chuck Dinerstein, MD, MBA
Director of Medicine
Dr. Charles Dinerstein, M.D., MBA, FACS is Director of Medicine at the American Council on Science and Health. He has over 25 years of experience as a vascular surgeon.
