Cacio e pepe can be made with tonnarelli (like square spaghetti), bucatini (like thick spaghetti with a hole through the middle) or spaghetti.Julie Van Rosendaal/The Globe and Mail
Cooking is a science, so who better to tackle the challenge of finicky cacio e pepe – the iconic Roman pasta dish – than a group of phase matter physicists?
Cacio e pepe, which translates to cheese and pepper, is a simple combination of ingredients with a texture that’s tricky to master, even among experts: emulsifying pecorino, a hard Italian sheep’s milk cheese, with starchy pasta water and plenty of ground black pepper requires a delicate balance between heat, starch and moisture; proteins in the cheese can quickly make your sauce separate, or go lumpy.
Earlier this year, eight scientists from institutes in Spain, Germany, Italy and Austria dove into the physical properties of the sauce, isolating and analyzing each factor and presenting what they call a scientifically optimized recipe that enables a consistently flawless execution of the classic dish.
“The concentration of starch plays a crucial role in keeping the sauce creamy and smooth, without clumps or separation,” their study, titled “Phase behavior of Cacio and Pepe sauce,” reads. They determined that pasta water alone is inconsistent, and doesn’t always contain enough starch to stabilize the sauce effectively; if the starch content is less than 1 per cent of the weight of the cheese, the sauce is prone to separating into clumps – anything over 4 per cent and your sauce may stiffen as it cools.
Their solution was controversial, as solutions often are, but made sense – they ensured consistency of the starch level by making their own cornstarch and water mixture, calculating that starch should be between 2 and 3 per cent of the weight of the cheese. It’s a simple trick, and it works.
“One of the benefits of this stabilized sauce is its ability to withstand reheating,” they wrote. “Unlike traditional methods that risk clumping or separation, this sauce maintains its texture and stability … this ensures the dish can be served hot, allowing diners to enjoy it at its best.”
Cacio e Pepe (for two hungry people)
Cacio e pepe can be made with tonnarelli (like square spaghetti), bucatini (like thick spaghetti with a hole through the middle) or spaghetti. As for the cheese: the scientists say traditionalists insist on using only pecorino, though some argue that up to 30 per cent parmesan is acceptable. Below is their optimized technique, edited for length and home cook-friendly language, and with a higher quantity of water for the cornstarch mixture – theirs calls for 40 grams, which made it very thick when heated in a small saucepan, but they suggest adding more water as needed.
- 240 g dry pasta (tonnarelli, bucatini, spaghetti)
- 100 g water (about 1/2 cup)
- 4 g cornstarch (2 tsp.)
- 160 g Pecorino (and some Parmesan, if you like)
- freshly ground black pepper
In a large pot of boiling water, cook your pasta until al dente, saving some of the starchy pasta water before draining.
Meanwhile, heat the water and cornstarch until it thickens and goes from cloudy to nearly clear. (Add a splash more water if it gets very thick.) This process, known as starch gelation, increases the viscosity of the mixture. Once the starch solution is ready, allow it to cool slightly by either waiting or mixing it with a small amount of cold water.
The next step is to combine the starch solution with the cheese. Manually grating the cheese is not ideal, since it leads to chunks of different sizes. Blending it with the starch solution makes a smooth, homogeneous sauce. (This is easy to do if you grate the cheese first, then blend it with the starch mixture and a hand-held immersion blender.) If blending is difficult, add a splash of water to ease the process, and season with freshly ground black pepper to taste. (If you time it right, you can add a splash of the starchy pasta water.)
Once the pasta has been drained, let it cool down for about a minute to prevent the heat from destabilizing the sauce. Toss the pasta with the sauce, over low heat if you need some warmth, adding some reserved pasta water as needed until you have a smooth sauce that coats the pasta. Serves 2.
