Enhancing Food Flavors, Part 4
Why do we use salt? What is it about salt that makes us use it in so much food, and so many preparations?
Salt is an amazing thing. It is chemically-speaking the most simple molecule that we eat (2 atoms as compared to three in water), and along with water is the only non-organic substance that we consume in macroscopic quantities (large enough to be seen with the naked eye). Everything else we eat and drink comes from some living source, be it plant or animal (counting fungus as a plant). All organic materials are built from chains of carbon atoms that can join, split and recombine in almost unlimited ways, which gives us our proteins, starches, fats, oils and flavor compounds. All sugars are made of carbon chains, and even the chemical processes that happen to sugar do not change this fact. If yeast eats sugar, it changes the sugar to ethanol (2 carbon atoms) and carbon dioxide (one carbon atom). This is the process that turns grapes into wine, and if you continue the process, letting bacteria to eat the alcohol, it will turn into acetic acid, or vinegar, which is also composed of two carbon atoms. All life is based on organic molecules. Everything we eat and taste is made from carbon chain molecules.
But not salt. So why do we eat it? We must need to eat it, because the tongue is so sensitive to it. Of the few major tasting sensations we are able to detect, saltiness is the only one that derives from non-organic compounds. Clearly we are meant to be able to detect the taste of salt, and from the sensitivity we can conclude that we are meant to be able to detect minute amounts of it. The reason we need salt turns out to be the sodium. Sodium, when dissolved in water, is electrically charged and becomes an electrolyte. Along with Potassium, Calcium, Zinc and a few other trace minerals, it is responsible for allowing electrical charges to flow through the body (nerve impulses), and various materials to flow in and out of cells through the cell walls. Without these electrolyes life simply stops, since the cells have no way to communicate, receive nutrients or expel waste.
But the magic of salt does not end there. Aside from its life-supporting qualities salt has many other fascinating properties that make it indispensible to cooking and cooking processes. If you were to make a comprehensive list of all the major and minor types of cuisine around the world, and made a list of the ingredients that are used in each, I suspect that salt would be the ONLY one besides water that would be universal. To that end, salt is Number One on my list of must-have ingredients, and I always make sure that I have a spare box of it.
All chefs will tell you that you must season your food as you cook it. In fact, they will season their food at every stage of the cooking process. One of the reasons why is that salt has hygroscopic properties, meaning it will pull moisture from surrounding materials. This has a number of positive effects in cooking, as well as in various preparations.
The first benefit of hygroscopy is that it pulls flavorful compounds along with moisture from deep within the cells of the food. This lets more flavor compounds reach the tongue, allowing for maximum flavor sensation. The second benefit is that by reducing the amount of “loose” water in food, we can reach a higher cooking temperature. Wet food will evaporate water as it cooks, which means that excess heat is given off and cooking temperature is limited to the boiling point of water (212 degrees, or 100 Celcius). If you can get the temperature higher, you can get even better cooking effects such as carmelization. If you want an extreme example of the benefit of carmelization over boiling, try brussels sprouts cooked by both methods, and decide which one you like best!
The third benefit of hygroscopy is not really related to seasoning food, but has more to do with preserving it. If you add enough salt to food, it will draw all or most of the moisture out of it. By doing this it reduces the chance for bacteria to multiply and ruin the food. Bacteria, like most living things, require moisture in order for the chemical reactions that support life to occur. Remove the water, and they cannot multiply. This type of preservation is perhaps the oldest, with the possible exception of air drying, and it is a lot less chancy than simply letting food dry in the air.
Besides attracting and holding water, salt has some other useful chemical characteristics. One of these is the ability to change the boiling or melting point of water. If you dissolve salt in water you will increase the temperature at which it will begin to boil. This means that you can cook the food at a higher temperature, and thus cook it faster. How much hotter? Well, if you use the maximum amount of salt that will dissolve in the water, you can increase the boiling point by a whopping two whole degrees! Okay, that is not a lot, but what is really interesting is that you can decrease the freezing point of water by adding salt, and this is much more useful to us. By letting water get to a lower temperature we can do all sorts of amazing things. Non-culinary examples include melting the ice on your driveway in the winter, and delivering sub-freezing temperatures to ice rink surfaces (many ice rinks use saline solutions rather than more dangerous chemicals because of the large quantities required and the danger of leakage). But my favorite usage of salted water is in the making of ice cream.
Ice cream can be made by hand using simple household items. I saw this on a show call Food Jammers on Food TV, where they used two cans, one that fit inside the other. The inner can had the flavored cream, and it was closed and placed inside the larger can. The space between the cans was filled with ice, and then salted. The outer can was then sealed, and they proceeded to kick the can around to agitate the cream, and get it to freeze. While the first attempt failed due to poor sealage, the next attempt resulted in amazing ice cream. The really amazing thing was that they did this at a camp site, of all places, and all the flavoring was found in the woods nearby. The salt was absolutely vital to this success, because it melted the ice without raising its temperature. The melting allowed for a greater transfer of heat between the two cans, drastically speeding up the freezing time. If they had simply used plain ice it would have taken hours. As it was, I believe it was around 30 minutes with the salted ice.
To be perfectly honest, most soluble materials will have the same effect on water, but most of them should not go near food; anti-freeze is one such material, but I think you will agree that ice cream and antifreeze should not ever come near each other.
In addition to these chemical properties, salt also possesses some interesting gustatory effects. Human tongues can detect five or six major flavor categories: Sweet, sour, spicy, salty and bitter, with the more recent addition known as “savory”. While the latter is perhaps a more of a complex groups of flavors, the other five are very simple, basic flavor sensations. Good cooking requires a good balance between these, and there should always be at least two of these present in any dish. In fact, classic Chinese gourmet cuisine requires all five to be present. However, for most of us, the bitter taste sensation is not all that pleasant, and we often want to do something to reduce or eliminate this from foods that we would otherwise enjoy. This is where salt comes to the rescue again. Our ability to taste saltiness is so sensitive that it actually blocks out the abililty to taste bitterness! By simply adding salt to something bitter, we can block out the sensation of bitterness without doing anything else! I am not sure why this is, but perhaps it has to do with the fact that bitter sensation is actually something of a warning mechanism: most poisons have a bitter taste to them. Perhaps the “positive” taste sensation and “negative” ones are simply wired on different nerve paths, and they can’t both operate at the same time. This is pure speculation on my part, but what I do know is that salt trumps bitter every time. (It will probably take Science several decades to catch up with my advanced thinking).
Fortunately, the same does not happen with sour, sweet and spicy foods. In fact, the addition of salt actually enhances these flavors, and it does so in two ways. First, saltiness will “wake up” the palate. The presence of salt seems to make the other sensations more readily detected in the exact opposite way that it seems to decrease the sensation of bitter compounds. The addition of salt does not add more of the other flavors; it simply allows more of them to be absorbed, much like eye drops causing the pupils to dilate and letting more light in. And at the same time, salt acts as a contrasting element, especially when it comes to sweet things. At first thought it seems odd to add salt to sweet things, but the effect is really amazing. This is the reason why chocolate and peanut butter go so well together; their flavors play off each other, maximizing the sensation of each element. I guess it’s the same thing sort of thing as putting a diamond on a black background, where the contrast actually makes the diamond seem brighter than if it is sitting on a white background.
By no means have I covered all that there is to know about salt. Some things that I may cover at another time are Fleur de Sel, Kosher Salt vs Iodized table salt, and using salt as an actual cooking vessel. I also did not touch on the dangers of too much sodium in the diet. But I hope I have done enough to convince you of salt’s true value in the kitchen, as well as in life.
Yours in Good Taste,
Erik Christensen