The scientific formula behind the perfect carbonara pasta

The first to lay the groundwork for the “scientific carbonara” was the chemist Dario Bressanini in 2008, in his “Scienza in cucina” column for the magazine L’Espresso. Like all his articles, this one is both interesting and simple to understand, well within the grasp of anyone with a basic knowledge of cooking and a food thermometer. I’ll try to summarize it just as clearly.

For the egg in carbonara to come out right, Bressanini explains, you must keep its chemical composition in mind, and the fact that it is composed of various proteins that coagulate at temperatures below 100°C. The yolk and white contain different percentages of water, fat (only in the yolk) and proteins. The latter play a pivotal role, because when heated, they break down and form a web that can trap and hold water molecules.

But if the heat is too high, this web ‘contracts’ and expels the water molecules, becoming completely solid and dry. The yolk, which is the part of the egg that interests us most for carbonara, starts to thicken at 65°C and becomes completely solidified at 70°C. The white instead contains various proteins, including ovotransferrin – which makes up 12 per cent of the yolk and starts to coagulate at 62°C, becoming solid at 65°C – and ovalbumin, which makes up 54 per cent of the protein in the white and coagulates at 85°C.

If you are making the sauce with yolks alone or with a low percentage of whites, then to obtain that coveted creaminess, you should stay below 65°C. Otherwise, you will end up with scrambled eggs on your pasta, the effect now considered most execrable.

Italian traditional pasta alla carbonara (Photo: Getty)

With these basic principles in mind, various food writers and cooks have come up with strategies to guarantee perfect results every time. Laying aside the method that calls for adding the raw eggs to the freshly drained spaghetti, which is the most traditional but also has the outcome most difficult to control, there are at least two other options.

The first is to make a savory zabaione to add to the spaghetti.

This is done by combining the yolks and whole eggs (a possible ratio is one whole egg and two yolks to 160–180g of spaghetti, but one could also use just the three yolks) with the grated cheese (black rind pecorino romano or parmesan, or a blend of the two, totaling about 80–100g), three or four tablespoons of water, and an equal amount of the rendered fat left over from frying the guanciale. This mixture should be poured into the top of a double boiler set over simmering water, whisking constantly.

The mechanical action of the whisk and the rising temperature will make the proteins in the yolk start to break down, trapping the water and air inside, until it completely coagulates at around 70°C. To ensure just the right texture for your carbonara, it’s best never to go over 63–64°C. Why? Because slightly varying proportions of yolks, whites, water and cheese could affect the outcome, so a keen, watchful eye is still necessary.

Once the desired temperature is reached, you should immediately remove it from the heat, while still mixing to continue incorporating air. If necessary, this operation can be repeated more than once, putting the top of the double boiler back over the simmering pot until the sauce reaches the desired consistency. If the mixture is a little too thick, you can add a small amount of cooking water while stirring in the spaghetti (off the heat) to obtain the perfect density.

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When your savory zabaione is ready, it can be added to the drained spaghetti along with the fried guanciale and the pepper; just make sure that the pasta temperature is not much over 70°C, otherwise all your efforts could be wasted.

The second option involves using a device that keeps the water in a vessel at a constant, controlled temperature, for the “sous vide” method of cooking.

In this case, all the ingredients listed above should be put in a heat-safe plastic pouch, and immersed in a water bath at 63°C for about an hour.

Once the time is up, pour the mixture into a bowl, whisking vigorously, and pour it over the cooked pasta. With the aid of a simple kitchen thermometer or a sous-vide machine, these two techniques will give your carbonara that perfect, velvety texture every time.

A Brief History of Pasta: The Italian Food that Shaped the World by Luca Cesari (Profile Books, £16.99)

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