The ultimate mover and shaker: Swetha Sivakumar on salt
As they melt away, salt molecules move in and out of food, draw water out of ingredients, seep into meat. Take a whirlwind ride. In this week’s Sound Bites.
Why does salt vanish so quickly when added to water? Well, that has something to do with the nature of water itself.
The sodium-chloride (NaCl) molecules are torn apart by the polar nature of water, because the negatively charged oxygen atoms in water draw the sodium ions, and the positively charged hydrogen atoms draw the chloride.
This reaction makes it possible for salt to move within foods with ease. But what else is happening, when salt is not alone in the water? This makes for some really interesting study.
A key superpower of salt is that it can alter ingredients because it can cause osmosis; that is, it can make water move in and out of a semi-permeable membrane.
It is this process, for instance, that sees water pulled out of raw, chopped vegetables when salt is sprinkled on them. The semipermeable membranes here are the cell walls of the cut vegetables. Because of the attraction between the positive and negative ions of salt and water, the water in the vegetable is drawn out, to where the salt is, until the salt is dissolved.
Now the water and salt are one solution. If one lets the vegetables sit for a while, some of that solution will be absorbed back into the vegetable’s cells, salting the vegetables on the inside. Which is why a side salad seems so much richer in flavour when we follow these simple steps — as opposed to when we simply sprinkle salt and eat at once
This is also why salt is added to dishes early in a cooking process, so that it can flavour ingredients from the inside out. And it’s why adding salt at the table yields a flavour so different: sharper, less blended and more blinding to the tastebuds.
Meats are brined even before the start of a cook for this reason, although most people vastly overestimate how long salt takes to act on raw meat.
In a test done by the TV show America’s Test Kitchen, for instance, meat was soaked in a standard brine for two, four and 24 hours. A chemical test was used to identify how far the salt had travelled into the meat.
At two hours, the salt had penetrated to a depth of a third of an inch. At 4 hours, half an inch. And at 24 hours, three-quarters of an inch of a standard cut of pork loin. So a day doesn’t really add much; just 30 minutes is enough for salt to make its way below the surface.
Dry-brining meat (just adding salt) also yields a succulent result. In the book Modernist Cuisine: The Art and Science of Cooking (2011), the authors — artist and chef Maxime Bilet and technocrat and food photographer Nathan Myhrvold — explore how the negatively charged chloride ions in salt act on muscle fibres. These ions insert themselves between the fibres, causing the fibres to swell.
When heated, these swollen fibres are able to retain more of the water within the meat itself. Without the brining, the meat fibres shrink more rapidly and allow far more water to be lost when heat is applied.
How much salt does it take to do all this? New cooks are often intimidated by the question of how much is enough. They tend to under-salt a dish, for fear of over-salting it. And few things taste quite as disappointing as an under-seasoned meal.
My favourite hack for how much is enough came to me from the Iranian-American chef Samin Nosrat, one of my favourite food writers. In her book Salt, Fat, Acid, Heat (published in 2017 and turned into a Netflix show in 2018), she suggests that one keep adding salt until, on tasting the dish, one experiences a “zing” in the mouth, almost like a tiny jolt of electricity.
For those who prefer precision, a healthy lower end is considered to be 0.5%. If cooking 1 kg of vegetables, that’s 5 gm of powdered salt (or about 1 tsp).
Now, 1 tsp of powdered salt is saltier than 1 tsp of rock salt, because the latter is far less dense. The large grains of rock salt crystallise with more air trapped between the molecules, while regular iodised salt is made by a quick-evaporation process that produces far-more-compact crystals.
So, just weigh the salt. If its 5 gm, whether powdered or rock, the flavour result will be the same.