Cooking pasta is easy, yes? For every 100g of dry pasta it’s one litre of water and 10g salt on a rolling boil? And a bit of olive oil? Wrong on all counts.
This was prompted by a reader question – oil or salt? – and I started the answer ‘just salt’ then double-checked the science because some readers will nail me on dodgy assumptions in a heartbeat. Bastards. And it turns out I was wrong. But my usual bible might be too…
Why add salt to the water when cooking pasta? Some say it makes the water boil at a higher temperature so the pasta cooks faster, some say it makes the pasta less sticky by inhibiting starch gelation. True, adding salt will increase the boiling temperature. But adding a whole ounce of salt to five litres of water means it will boil at 100.1°C instead of at 100.0°C. In scientific terms that’s less than a Gnat’s Knacker (gKn) – consider that on top of Ben Nevis it probably boils a couple of whole degrees lower due to altitude. So, to significantly affect boiling temperature you’d need soooooo much salt the pasta would be inedible.
What about gelation? This the process where starch granules absorb water and swell up. Heat them some more and they burst. For wheat flour the gelation range is 52-85°C. They also start to leak a bit which is why pasta tends to stick together at the start of cooking if you don’t stir it.
If you read the literature it basically says if you add a little bit of salt you might stop it sticking a bit, add too much you’ll make it worse. But it depends on the salt, the pasta etc etc. And when looking at starch chemistry in a lab you’re controlling the variables you get at home like purity / hardness of water, type of salt as well as type of pasta and time.
OK, heresy time. I think McGee might be mistaken. He says salt in the cooking water slows gelation – which is generally true but the swelling of wheat starch granules is pretty much unaffected by salt unlike, say, potato starch. But this is nit-picking; scientifically salting the water might have limited utility but if you don’t the finished pasta will be bland and that can’t be fixed by adding salt to the sauce.
You don’t need as much water as you think. Harold McGee wrote about this recently and it’s quite startling. He nails the idea that pasta needs a large volume of water at a rolling boil to keep the pasta separated.
But what about the argument that a larger volume of water is necessary as it will retain heat better and so will come back to the boil quicker? It’s nonsense. It doesn’t matter if you put your pasta into a large body of water or a small one; it takes the same amount of energy to bring it back to the boil. The temperature of a smaller volume of water might drop more but it still requires the same amount of energy as a large volume to bring it back to the boil. (I won’t complicate this with surface area to volume ratio arguments).
But does it need to boil? No. Pasta is granules of starch held together with protein. When you boil it the granules of starch swell until they burst, releasing starch. This is why pasta tends to stick together at the start of cooking – the starch is acting as a glue. (Probably because it is; we used to stick up wallpaper with it.)
What you actually need is >80°C, not necessarily a rolling boil. What you’re really after is that point where all the starch has softened and the proteins have coagulated to hold it together so you get that perfect al dente finish. If you put the pasta into boiling, salted water, stir, put the lid on and turn off the heat the temperature won’t drop much. And you’ll get perfect pasta. Try it.
This I’m not convinced about. You can form a very thin layer of oil on top of water and when you stick stuff through that layer into the water you can coat it. But at a simmer or boil? That’s a chaotic thing to expect to behave the way a bilayer would in a lab. McGee says you can lift spaghetti etc through the surface while it’s cooking to lubricate it and stop it sticking. Can’t see it.
Also, if you want to put butter and parmesan or aglio e olio onto freshly-cooked pasta, great. But if you’re covering it with a sauce don’t add oil or the sauce won’t stick properly. Put the cooked pasta into a pan of hot sauce straight away and get it coated. It will stick far better.
Don’t try this with fresh, egg pasta. It will fall to pieces. You need to set the egg protein super-quick to give it structure or you’re knackered.