Why oil doesn’t get salty when adding salt to potatoes while frying?

Question

I use to fry potatoes reusing the same (olive) oil several times (about 5-6 times), and I salt them while frying. But the the oil doesn’t get salty. What’s the reason for that?

In: 2000

Answer 1

Salt is a compound of two atoms, sodium and chloride. The sodium has a positive charge and the chloride a negative charge. Things with opposite charges like to stick together, so they make salt crystals. Water isn’t charged, but it does have a side that’s sort-of negative and sort-of positive. When you add salt to water, the positive side of a bunch of water molecules surrounds the chloride atoms and the negative side of a bunch of other water molecules surround the sodium and pull them apart. There’s no longer a crystal but a bunch of individual atoms (called ions, because they have a charge) floating around in the water, which is called dissolving, and what you taste as “salty” is those ions interacting with your tongue, rather than the crystallized salt. Molecules that can dissolve easily in water are called hydrophilic (water loving) and are either charged like the sodium and chloride, or have the same sort-of positive/negative setup of water.

Oil, on the other hand, is hydrophobic (water hating). Oil molecules have evenly-distributed charges throughout, with no consistent positive(ish) or negative(ish) parts. Without that they can’t pull the sodiums or chlorides off the larger crystal, so it just stays as a chunk. In fact, if you poured the used oil into a narrow enough container and let it sit for a while, you’d probably see a layer of salt accumulate on the bottom.

If you salted the oil heavily enough to start, the potatoes might pick up enough by chance as they fry to be well-seasoned, but most of the salt is probably from when you salt them directly. If you taste the oil, you might get a little salt from whatever crystals you happen to pick up in the spoonful, but they would have to dissolve in your saliva first, unlike when the salt is in water and just has to mix up with your saliva-there’s a whole extra physical/chemical step that has to happen.