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In general, you are absolutely correct. Naturally, it’s a bit more involved than that, so let’s examine what sorts of things salt does, and when/how it can be best used.
At its best, salt is a flavor amplifier. While salt does have a distinctive flavor of its own, and there are people who love that flavor especially, salt really shouldn’t be tasted in the food that you’re serving. Instead, you should add just enough salt to bring out the flavor of the food but not enough to taste the salt itself.
Now, there are those who feel that salt is a flavor crutch, and in many ways it is. We tend to over-season our food. Seasoning is the word to use when you’re adding salt to enhance the flavor of food. However, if you were to halve the amount of salt you add to your food, and stayed away from restaurant and processed food, you would find that you can taste the flavors of food just as well as you used to before. It’s kind of like seeing in a darkened room, once your eyes adjust, you’re fine, but when a bright light comes on, you won’t be able to see in dim light for a while. The same happens with the palate.
Of course, if you do ever go out to a restaurant or eat anything seasoned by someone else, it tends to be easier to use your normal amount of salt. Cooking at home from scratch, you’ll still use a lot less salt than you would get from most processed foods. By and large, salt is good for people. We need it to run properly down to the cellular level. Unfortunately, some people are sodium-sensitive, meaning that their blood pressure increases with excessive salt intake. If you are one of those people, chat with your doctor or a nutritionist about how much salt you can handle. For the rest of us, even canned soup isn’t going to hurt with all of its salt.
As for seasoning strategies, a lot of it comes down to the difference between surface area and volume. If you had, say, a casserole, and you cooked all of the ingredients without any seasoning until you had a completed, bubbling casserole ready to serve. Then you sprinkle some salt on top of the casserole. What will happen? Well, you’ll have a layer of salt, and a layer of unseasoned casserole. You’ll get some amplification of flavor, but by and large, you’ll get a combination of bland and salty. Even moreso, you’ll have people adding salt to every bite, so that they can extract some flavor from the food, which tends to use up a lot of salt.
However, if you were to add salt along the way, so that each of your components were seasoned properly then combined together, then you wouldn’t have any excessively salty flavor, and all of the flavors of the food would be brought out well.
Salt does other things than flavor amplification, though. Salt on the outside of a cell membrane, say with some beef, will cause the water inside those cells to leave and collect on top of the meat. Once that water is cooked away, you’ll have everything else left over on that layer except for the water. All of the things that provide flavor will be left in an undiluted form, which, with the proper application of heat, will become a flavorful crust when the Mailliard reactions take hold.
Similarly, if you take a 20:1 ratio of water to salt, by weight, and soak an easily dried piece of meat like a chicken, turkey, or pork in it for a few hours, that brine will carry salt and water into the cells that make up that cut of meat. Then, when you cook it, you not only have a juicier meat that is resistant to drying out due to overcooking, but you also have the seasoning infused into it as well, bringing out all of that flavor.
Plant cells have an extra layer of protection called the cell wall. It’s why plants are crunchy and meat is not. Adding salt to a cooking vegetable will help break down those cell walls, allowing their juices to release. This is an important part of sweating vegetables (also known as the soffritto).
Salting ground meat has the effect of tightening up the grain of the meat. It’s the difference between a sausage patty and a hamburger. Because ground meat has a lot more surface area than a whole piece of meat, adding salt into that will give it a lot more access to the cells, so the salt can have a larger effect. With a whole meat, it’s only a layer that gets affected; with ground meat, it’s all of the cells. For more information, The Burger Lab from Serious Eats did a great article on salting hamburger.
Another time you don’t want to salt early is when you’re making anything that’s going to reduce significantly in volume. This means stock, sauces, etc. If you season early, and you taste your seasoning to ensure that it tastes good for the expanded volume, then it’s going to be salty once the volume reduces. In this case, it’s best to wait until the dish is at its final volume before seasoning that part. Fortunately, food that is mostly liquid is easy to stir, so any salt you add can be thoroughly mixed into the final product, rather than just sitting on top.
I hope this helps to clarify the usage of salt. Along with controlling heat, this is one of the most critical and basic skills that you can learn to make food taste its best. Naturally, practice is key, but I find that knowing some theory while you’re practicing can help quite a bit as well.