How many times have we heard “grandma’s trick” by adding a drop of oil to the pasta water? Let’s dispel a myth right away: the oil in the pasta water is not needed to prevent it from sticking. This is one of the most widespread false beliefs in kitchens (Italian, but especially foreign) and is based on the mistaken belief that oil, being a natural lubricant, is capable of preventing pasta from sticking.
The scientific reason why this trick it does not work it’s very simple: water and oil they don’t mix. At school they teach that «like dissolves like»: in principle, non-polar substances (in which the electrical charges are distributed symmetrically in their molecule) dissolve non-polar ones, while polar substances (with an asymmetric distribution of electrical charges) dissolve polar ones. Water is a polar molecule (more “negative” in correspondence with the oxygen atom and more “positive” in the two hydrogen atoms), while oil is apolar. So there is no story: the oil is hydrophobic and, if brought into contact with water, it will form a layer on top of the water due to its lower density.
In practice, therefore, if we add oil to our cooking water, it will not be distributed evenly throughout the pan but it will remain confined to blobs suspended on the surface of the water and therefore it will hardly come into direct contact with the pasta. And if the oil is not able to reach the pasta, it is clear that it cannot even “separate” it: it is therefore a false belief.
The pasta producers themselves, in their FAQs, they do not recommend using oil in cooking waterprecisely because the two elements do not mix with each other.
At this point, what is the best method to prevent the pasta from sticking during cooking? To know this we must first understand why the pasta sticks together when we cook it: this happens because thestarch contained within it tends to become sticky with high temperatures. The best way to prevent the pasta from sticking, therefore, is cook the pasta in plenty of water (to decrease the starch concentration) and mix frequentlyespecially in first 2 minutes of cookingthat is when the pasta releases the greatest quantity of starch.
