Does it do any good to cast oil on boiling pasta water? Can the oil keep noodles from sticking together? These days, the position of many Italian cooks is a firm no.
Not only does the oil float aloofly at the top of the pot, they observe, but oily pasta is less able to hold sauce on its surface. It is far better to use a great excess of water, stir the noodles constantly and toss them with the sauce immediately after draining them.
That makes good sense. But if my biggest pot is otherwise engaged, or I can't give my undivided attention to the cooking noodles or my children like to do their own saucing on the plate, can a bit of oil help?
To find out, I dyed some oil a contrasting dark orange with annatto seeds, then brought a large pot of water to the boil, poured on a scant tablespoon of oil, dropped in a pound of spaghettini, stirred the pot for about a minute and watched it cook. The falling pasta and roiling water broke the initial floating oil puddles into hundreds of droplets that dispersed in the pot and then rose only slowly to the surface.
When the noodles were done, I removed some by scooping with a strainer, and the rest by pouring the contents of the pot into a colander. Just as the noodles had passed through the oil on their way into the water, so they passed through again on their way out, with both methods of removal.
All the noodles were tinged with orange! Sure enough, after pulling and probing them, my fingers took on a light sheen of oil. And given my minimal stirring, surprisingly few noodles were glued to each other. After sitting piled in the colander for 30 minutes, many more had become stuck, but not irreversibly: I could tease them apart.
So some of the oil in the cooking water does coat the noodles, enough to help keep them from sticking to each other. But does oil compromise the marriage of noodle and sauce? Chinese cooks don't think so; they often oil their noodles before saucing. I put marinara sauce on side-by-side plates of oiled and unoiled spaghettini, ate both and found little difference in the amount of sauce left on the plates. Most of it is cradled in nooks between neighboring noodles.
So if you're worried about sticky noodles, forget the prevailing opinion and cast that oil.