It seems like simple arithmetic.
You add salt to food, and it brings out the flavor.
Unfortunately, it’s not necessarily that simple. That’s why, when I’m eating somewhere, a main thing I take into consideration is the way salt is being used in a dish. The extent of doneness of the components in the dish, the balance of flavors, and the way salt is used are the three things that will make or break a dining experience whether you’re eating waffles and hot dogs on the street or foie gras at a fancy restaurant in France.
What prompted me to sit down and think about this is the steak I had at Crossroads at the House of Blues in Florida. The steak I was served was beautifully cooked, had a tremendous amount of spices that brought flavor to the game, but the damn thing had no salt. It’s unfortunate, but a common trend.
I’m opposed to the growing mentality at crowd-pleasing restaurants that low sodium should be the default; I’ve seen it a thousand times, someone who’s on a low salt regimen will specify that every time they order out.
In the case of the steak (or pretty much any animal protein), salt prior to cooking serves a very specific physical purpose. A piece of meat is made up predominantly of water. That doesn’t mean that you can dry it off and keep pouring water out. The water is retained within the protein structure. Salt is able to draw some water out of the proteins (osmosis), and this facilitates some unfolding of the proteins to accommodate the loss of water. This, in turn, makes the stars align to make Mallard reactions happen (that’s how the nice crust is developed). This is all technical stuff, and I could break it down further (the joy of being a chemist!), but it proves the point that salt is a crucial early ingredient to cooking proteins.
Salt also has a flavor, and it’s not like you can cake salt all over stuff and things will work. The way salt interacts on the tongue is an important consideration in how much to use. The cartoon-y way I like to think about it is that the receptors on the tongue are waiting to be electrified, and the positive sodium and negative chloride ions provide the current to carry other flavors to the receptors. If there’s too much salt, the ions only serve to overload the receptors muting the other flavors. That (and the fact that table salt contains some iodine) is the reason why just adding salt to food after its cooked isn’t a solution to the matter. The application of salt is a tricky balance; that’s why I see it as a true skill of a cook or chef in the conception and execution of a dish.
There are some more areas where salt is crucial. For example, certain preparations of eggplant rely on the osmotic effect of salt. If you were to flour-egg-breadcrumb a slice of eggplant just after slicing it then fry it, you’d get a horrible, spongy mess (stand far away from the oil if you’re crazy enough to do this). By laying the slices out with a small amount of salt, water is drawn from the cells, helping them collapse, so that, by applying the same procedure, the result is a soft, creamy eggplant encased in a crust. The same is true for things like zucchini.
Tomatoes and other soft vegetables behave similarly. That’s why when you make a salsa and add salt, you’ll come back a few hours later and it’ll be watery. Another example is the way an awesome salami and tomato sandwich becomes a mooshy mess after sitting on your desk all afternoon. Sometimes, that’s the effect you’re looking for; sometimes it ruins your meal.
There’s a lot more to the story, though. What about cooking pasta? People add salt to the water to raise the boiling point, right? Wrong. People add salt to the water to season the pasta, because it’ll take the salt in better when it’s submerged in the water than if you were to take a salt shaker to it after draining. [It would actually take approximately 1/4 pound (1 cup) of salt in 1 liter of water to raise the boiling point of the water a barely detectable amount; that’s a lot of salt! Trust me, it’s too much salt!]
I could talk about this for hours, but I’ll stop here. Thinking about things scientifically helps understand why things are the way they are, and I think that helps with enjoyment across the board. So, when you eat something, pay some consideration to where in the preparation the salt is utilized, and really think about the effect of salt on the food.