Photo credit: shardayyy
As our June MOCA demonstrated, a few grains of salt doesn’t just make food salty; it seems to make some sweet fruits sweeter, mask unpleasant bitter tastes, and well, just make everything taste better.
In this post, we look at some of the recent research about salt to discover how this magical mineral accomplishes its flavor feats.
What is salt and why do we like it so much?
In chemical terms, a salt is any compound defined by the ionic bond of a cation (a positively charged ion) to an anion (a negatively charged ion). In table salt, sodium (Na+) is the cation and chloride (Cl-) is the anion.
The basic science behind why human beings crave salt appears to look something like this:
- The Earth is made up of lots of minerals
- Rain and rivers carry minerals into the ocean
- Salt is very soluble in water, so oceans get salty (other minerals turn into sand)
- Sea-based animals evolve to live in a salt-rich environment
- Land-based animals evolve from sea-based animals and their biological processes continue to rely on salt.
- Human beings need a proper balance of salt to survive, so we evolve taste buds that find it delicious.
Of all the nutrients we put into our bodies through eating, water is the most important and salt plays a crucial role in moving water around the body.
I find it easiest to think of salt as one half of the body’s water-regulation system, the other half being potassium. The membranes of every cell in the body allow water to flow through in direct proportion to how much sodium and potassium are present in the immediate area. Too much or too little sodium in the body affects everything from digestion to blood pressure to brain function.
Since proper sodium levels are so important, the body uses the kidneys to maintain a precise balance. The system is very efficient, which means that if you eat more sodium than the recommended daily allowance, you’ll simply excrete whatever you don’t need (within reason). That also means that we tend to crave more salt than we actually need to eat, which might explain its flavor-enhancing properties.
Salt suppresses some flavors…
We’ve already talked on this blog about how each of the basic tastes suppresses all the others. Salt is no exception.
Since all the basic tastes affect each other, it’s likely that some flavor suppression happens at the perceptual level–that is, your tongue may be tasting just as much bitter caffeine when a spoonful of sugar is added to it, but your brain concludes that the bitterness is tolerable in the presence of sugar.
But, salt’s ability to suppress bitterness appears to have a physiological explanation as well. To understand how, we have to look at how bitterness and saltiness are perceived on the tongue.
Bitter compounds are detected via taste buds when they bind to G protein-coupled receptors.* Human beings have at least 25 or so of these receptors and each bitterant can bind at different strengths to multiple receptors, which means people can taste a wide array of “bitterness”–by some estimates, as many as 300 different types of bitterness.
Salt, on the other hand, doesn’t bind to anything. The sodium ions simply pass through membrane channels that detect its presence–either salt is present, or it’s not.
Think of salt and bitterness as the fast and slow lanes at a toll booth. Bitterants have to go through the slow lane and every car gets carefully inspected and assigned a unique toll. Salt simply passes under an RFID scanner that counts the number of cars and charges each the same amount of toll.
Why does this matter? In 2001, Russell Keast, Paul Breslin, and Gary Beauchamp of the Monell Chemical Senses Center discovered that it is the sodium half of the NaCl molecule that suppresses bitterness. They also discovered that sodium suppresses different types of bitterness at varying levels and that other cations (such as lithium) can have a similar effect.
Here’s one explanation of why this is happening. We know that bitterness is detected by G protein-coupled receptors, but it also appears that the bitterness signal those receptors send to the brain require both Calcium and Sodium (both cations) to be sent properly. This may be part of how the presence of cations interferes with the bitterness signal, but the research is not yet conclusive.**
*G Protein is short for guanosine nucleotide-binding proteins, a family of proteins that allow detection of molecules (like those responsible for tastes) outside of a cell. See Alex’s post on the olfactory system for more information on how they function in conjunction with the coupled receptors..
**The mechanisms may not be conclusive, but in this 2003 review article, authors Keast and Breslin argue that previous research can conclude that suppression of bitterness by sodium must have a physiological component.
…And enhances others?
Here’s where things get tricky. A very straightforward experiment carried out in 1994 demonstrated that neither salt nor MSG, another well-known “flavor enhancer,” actually enhance flavor at all.
So why, then, do chefs and food scientists around the world refer to these two compounds as flavor enhancers?
There are two good explanations.
#1: Differential suppression
There’s nothing new to this explanation. We know that sodium suppresses bitterness and that bitterness in turn suppresses other flavors, like sweetness and sourness. What happens when you add salt to a complex dish that includes all these elements? The salt suppresses the bitter, which in turn allows greater perception of sweet and sour.
In real life, the subtle balancing act of all these taste components along with the myriad possibilities of food aroma define the art of cooking.
#2 Perceptual or physiological enhancement of aroma
The argument goes something like this: the inclusion of salt reduces water activity (Aw), which allows volatile aromatics to become more volatile.
Frankly, I think that’s a stretch. It seems much more likely that any flavor or aroma enhancement happens in the brain, at the perceptual level, rather than a true chemical change to flavor aromatics. Regardless, the research does show the effect, whatever its explanation.
What other flavor enhancers are out there?
The pharmaceutical and food technology industries are both very interested in developing ways to mask bitterness and accentuate desirable flavors. Recent awareness about the possible downsides of excess sodium intake and consumer preference for bitter nutritional ingredients has driven innovation.
Most of the recent research looks at monosodium glutamate, or MSG. MSG appears to have behave similarly to Sodium Chloride as a bitterness blocker and flavor enhancer, but it contains less sodium by mass and can be used in smaller quantities, while still achieving desired taste results, especially in savory or meaty foods.
- For more on MSG and other bitter-masking compounds, see this review article.
- And for more on the science of salt, see here.
Hopefully this casts some light on the mystery of salt. There are clearly some very nuanced effects of salt on flavor vs. aroma, or how exactly salt masks bitterness. Any way you cut it, salt cannot be ignored in any flavor balancing act.
Do you have any further questions about salt? Any weird effects you’ve noticed when using salt?