Do you have to cook pasta in salted water?
Martin Elsner is a professor at the Technical University of Munich and holds the Chair of Analytical Chemistry and Water Chemistry. He is also director of the Institute of Hydrochemistry at TUM, which contributes to improving the management of chemicals in the environment through research and analytical innovation.
"Pasta is made from durum wheat semolina or flour, water, and a bit of salt. If you could zoom in really closely, you'd see its porous structure. If we cook pasta in unsalted water, it quickly absorbs liquid and expands. If we cook it for too long, it would swell over time or completely dissolve in the water.
The reason for this is something some of you might remember from chemistry class at school: osmotic pressure. This occurs when two liquids with different concentrations of ingredients, the floury water in the pasta and the unsalted water around it, are separated by a semi-permeable membrane, i.e. the surface of the porous pasta structure. Due to osmotic pressure, water migrates to the side with more flour to create balance. This effect can be reduced by adding an ingredient to the cooking water: salt. Firstly, the water no longer penetrates the pasta as quickly. It ensures that the pasta does not swell too quickly – this helps to maintain its consistency. Secondly, the salt ensures that the pasta does not taste bland. If you add more salt, the salt sticks to the outside surface. When cooked in salted water, it is absorbed evenly into the spaghetti – it tastes better.
Whether the salt is added to boiling or cold water is largely irrelevant with today's stainless steel pots. It used to be different: In iron pots, corrosion could sometimes occur if salt was added too early. That's why people said you should wait until the water boils. It also makes almost no difference whether the water is cold or already boiling. Although salt raises the boiling point, meaning that water only boils at a higher temperature because of salt, the boiling point hardly changes with the small amount of salt. The only important thing is that the salt should be added to the water before the pasta is added. And with the pasta, too, it makes sense to add it only when the water is already boiling, as this makes it easier to measure when it is al dente. Similar to boiling eggs or baking in a preheated oven, this makes it easier to estimate how long the cooking time will be.
I used to add oil to the pasta water along with salt, hoping to prevent the pasta from sticking together. But I don't do that anymore. My wife explained to me that the pasta also absorbs the oil. This prevents the sauce from being absorbed properly later on – and I wouldn't want to miss that with her delicious sauce."
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