Italian scientists have discovered how to get a perfectly creamy pasta sauce every time, by analysing the physics involved in cooking cacio e pepe.
Cacio e pepe – meaning ‘cheese and pepper’ – is an Italian dish made with pasta, pecorino romano cheese and black pepper.
That may seem like a simple recipe, but it can easily go wrong. When hot pasta water is mixed with cheese, it can turn into a sticky mess of cheesy clumps in watery pasta, rather than becoming a smooth, creamy sauce.
So, Italian researchers – at the University of Barcelona in Spain, the Max Planck Institute for the Physics of Complex Systems in Germany, the University of Padova in Italy and the Institute of Science and Technology in Austria – came together to study the science behind creamy cacio e pepe sauce.
“We are Italians living abroad,” said study author Dr Ivan Di Terlizzi, of the Max Planck Institute. “We often have dinner together and enjoy traditional cooking.
“Among the dishes we have cooked was cacio e pepe, and we thought this might be an interesting physical system to study and describe. And of course, there was the practical aim to avoid wasting good pecorino.”
The study, recently published in Physics of Fluids, a journal of the American Institute of Physics, found that the key to creamy cheesy sauce was in the water.
Fats, like oil or cheese, generally do not mix with water. However, the pasta water added to the cheese contains starch, which should act as a stabiliser to create a creamy emulsion.
Study author Dr Daniel Busiello, of the Max Planck Institute, told BBC Science Focus that, when cheese is heated, its proteins "change their configuration" and stick together.
"However, the starch mitigates this effect by binding to the cheese proteins, reducing their direct interactions and, consequently, their aggregation," he explained.
The scientists found that the ideal pasta water for a creamy cacio e pepe sauce was 2 to 3 per cent starch, and they recommended not leaving the starchiness of your water up to chance.
“Because starch is such an important ingredient, and the amount of starch can sharply determine where you end up, what we suggest is to use an amount of starch which is precisely measured,” said Di Terlizzi. “And this can only be done if you have the right amount of powdered starch in proportion to the amount of cheese you’re using.”
So, the authors advise adding a measured amount of potato starch or cornflour to water, rather than pouring your pasta water straight into your pan.
They also recommend letting the water cool before adding any cheese, to help protect the cheese proteins from breaking down and forming unpleasant clumps.
For a perfectly even creaminess, the scientists advise first mixing water with starch, then blending this starch-water with cheese, adding this all to a pan and heating it up slowly. Then, add black pepper and pasta.
Busiello said that the scientists' recipe "remains faithful to Italian tradition," except for the use of powdered starch to control its amount.
"An experienced cook probably does not need our recipe," he said. "However, we offer a method to reliably prepare a traditional cacio e pepe that is foolproof, even in challenging situations such as cooking large quantities of pasta.
"Of course, we tested our method with more than two kilograms of pasta, and all the guests enjoyed it!"
Busiello added that measuring starch could prove useful for other Italian pasta dishes, such as spaghetti aglio e olio and carbonara, which also rely on a pasta water and cheese sauce.
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About our expert
Dr Daniel M. Busiello is a Distinguished PKS Fellow at the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, where he is working as an independent researcher. Busiello previously studied at the University of Salerno and the University of Pisa. Then, he moved to the University of Padova for his PhD on entropy production in non-equilibrium systems.
