Science

The Science of Salinity in Wine

Examining the complicated science behind salty-tasting wines, from the vineyard to the winery

Salinity in wine
Photo credit: iStock.

What makes a wine taste salty? And is a salty-tasting wine actually salty? These would seem like straightforward questions with, presumably, straightforward answers. Yet they’re not. Despite all the attention in recent years paid to salinity in wine, much remains unknown.

Let’s start with the latter question. “Taste” denotes how we perceive the compounds for which our tongue has receptors (salt, sweet, acid, and bitter compounds). Though it may be easy to measure the concentration of salts, acids, or sugars in a wine, those chemical measurements do not directly correlate to how we actually experience them—each taste affects the perceived intensity of the others. Salinity increases our perception of sweetness, but reduces the perception of acid. Sweetness reduces the perception of both salinity and acidity, and acidity boosts the perception of both sweetness and salinity. So, a high salt content in a wine doesn’t just make that wine salty, but makes us perceive it as both sweeter and less acidic than it is.  

Aromas, on the other hand, are sensed strictly with the nose. This includes when the wine is in our mouth as well as on the finish, after we’ve swallowed. Aromas further complicate taste perception, and may by association make us think that a wine is sweet, or even salty. For example, a wine with intense fruity aromatics may come off as sweet, when in fact it is dry.

Complicating matters even further is that any number of salts can cause salinity in wine. “[Although] the main mechanism in taste buds for perceiving salty taste is responsive only to sodium ions, the presence of chloride is also thought to be necessary as well,” explains Leigh Francis, the research manager for sensory and flavor for The Australian Wine Research Institute. “However, there is a secondary mechanism that responds to other ions, including potassium chloride, calcium chloride, and magnesium, which will contribute a salty taste.” 

Compounding the complexity: Leigh notes that these same compounds can also contribute bitterness, astringency, or a metallic taste. Salts in wine may also combine with acids, changing wine chemistry and taste. 

Salty Wine Origins

“Salt taste response is not really well understood compared to other tastes,” says Francis. Sensory thresholds of salinity in wine remain a mystery, and because other components in a wine affect how we perceive that wine’s salinity, the answer will likely be complicated and dependent on many other factors. In a 2019 study, published in the Australian Journal of Grape and Wine Research, the study’s authors speculated that the “salty taste” sensory threshold may lie between 384 and 482 milligrams of chloride per liter—a striking amount. 

For them, however, “salty taste” was also related to soapiness and “a slimy or soft mouthfeel” rather than the pleasant and desirable salinity—some at much lower levels—discussed in wines that are typically considered to be “salty.”

Roberto Taibo of Adega Moraima. Photo courtesy of Roberto Taibo.

One of the most famous “salty” regions is northwestern Spain’s Rías Baixas, where some vineyards are mere feet away from seawater. “In Rías Baixas, the wind and rain coming in from the Atlantic are rich in chloride and other salts of the sea,” says Roberto Taibo, the winemaker of family-run coop Moraima, in the coastal sub-region of Val do Salnés. “This influences the soil, little by little adding chlorides, phosphates, and sulfates, as well as potassium, sodium, calcium and other salts. This, along with our granite soil, leads to elevated minerality and wines rich in salts, particularly chloride.” 

The salts, then, are drawn into the roots and ultimately into the grapes. Taibo notes that wines in the Val do Salnés can reach salinity concentrations of 200 to 400 milligrams per liter—exceptionally high—with chloride being the most important salt in the region, followed by sodium and potassium.

But salts sneak into wines in other ways. Those deposited on leaves via wind, rain, or overhead irrigation are absorbed into the plant just like foliar fertilizers. Francis notes that overhead irrigation can increase sodium and chloride in wine by 50 percent versus drip irrigation.

This effect is also seen in other oceanside wine regions. In Greece, Yiannis Paraskevopoulos, the owner and winemaker of Gaia Wines, decided to test the salinity levels of three Assyrtiko wines produced at Gaia’s two wineries—one on the island of Santorini and one in Nemea, on the mainland in Greece. He had noticed that the Santorini wines typically carried an intense saline aftertaste—perhaps due to the fact that the island is located “in the Aegean Sea—a saltier sea than the Atlantic—[and] constantly blasted by gusty sea winds that get stronger as we approach harvest,” notes Paraskevopoulos—while the mainland wines did not. 

The results quantified what Paraskevopoulos tasted: The one mainland sample had 19.4 milligrams per liter of sodium, while the two vintages of Santorini wine held 54 and 68.5 milligrams per liter—on average, a 216 percent increase in sodium concentration.

Yiannis Paraskevopoulos of Gaia Wines. Photo courtesy of Gaia Wines.

In the Sherry region of Spain, known for its saline manzanillas and other dry sherries, Antonio Flores Pedregosa, the winemaker and master blender at González Byass, points out that Finos and Manzanillas from chalky albariza soils also have very high salt contents. “Depending on the level of calcium carbonate in the albariza [which ranges from] 20 to 40 percent depending on the vineyard, you get salinity levels between 40 to 60 milligrams per liter in some Finos and Manzanillas,” he says.  Albariza soils primarily contain calcium ions—hence their dazzling white color under the summer sun—but also a smaller proportion of sodium, potassium, magnesium, and other salts.

Sherry wines that are aged under a biofilm of flor yeast—including Manzanilla, Fino, Amontillado, and Palo Cortado—typically have particularly high saline characteristics. “The veil of flor,” Flores Pedregosa points out, “consumes nearly all residual [and normally unfermentable] sugars, can metabolize almost all of the glycerol,” and eats alcohol—the three components that contribute sweetness to a wine. Flor also lowers volatile acidity and produces acetaldehyde. 

All of these factors contribute to an increased perception of salinity in these already-salty wines. It’s no surprise, then, that these styles of sherry are famous for their salinity—not only do they get a high concentration of salt from the region’s soils and ocean proximity, but flor works in multiple ways to boost how we perceive it.

Salt, Soil, and Rootstocks

In the 2019 Australian Journal of Grape and Wine Research study on salt taste perceptions, when salinity was associated with a soapy, undesirable taste, the authors looked at irrigated vineyards in warm, dry regions, where salts build up on roots and natural acid levels may be low. All of these factors may be important variables in how salinity is perceived.

After all, rootstocks impact the amount of salt that gets into a vine. Since phylloxera, nearly every winegrower has had to decide what rootstock to use when planting a vineyard. In general, rootstock varieties lead to differing characteristics in a wine (though they don’t have as much of an impact as grape variety). This also relates to salinity—different rootstocks allow differing amounts of soil salts into vines and have different abilities to function in saltier soils. As rainfall is needed to flush salt build-up in irrigated regions, the ability of rootstocks to function well in saltier soils becomes more important as more regions face drought pressure from climate change. 

Antonio Flores Pedregosa of González Byass. Photo courtesy of González Byass.

The authors of a 2010 study published in the American Journal of Enology & Viticulture tested Nero d’Avola vines grown on sites with soils of differing salt content. Overall, they found that yield decreased on saltier soils, that sugar was unaffected, but that as soil salinity increased, so did polyphenols, anthocyanins, and various aroma compounds. It is worth noting that tasters preferred wines grown on the two more saline sites, finding the wine from the least saline site “flat and dull.” It is important to note that this is just one study.

Salinity, then, is an important taste component, as well as a modifier of many of a wine’s constituents. It’s therefore relevant to terroir. But here, as with so many other aspects, is where terroir gets tricky. The way that rootstocks regulate salt content is an example of how the human hand modifies terroir expression. Francis points out another: “Clearing trees for agriculture has an effect in Australian soils of increasing the water table, with salts being brought up from the soil profile.” Even clearing space to plant a vineyard can affect salt content in a wine. These examples can be added to the long list of reminders that there is no pure expression of terroir.

Salt in the Winery

Can anything be done in the winery to boost salt content? Salts are most connected in grape skins, so practices that increase extraction from those skins will increase salt concentration. Many Albariño producers, for instance, do a cold soak, crushing the pulpy grapes and letting them sit on the skins for a few days before pressing. This practice increases juice yield, as pectins break down during this time, and is a natural technique with similar goals to the use of pectolytic enzymes

This technique also increases the concentration of aroma precursors in must, boosting aromatic intensity and fruity character. This extraction prior to fermentation will result in less extreme aromatic differences and no relevant increase in tannins, relative to fermenting a white wine on the skins. Red wine, being fermented on the skins by definition, will see this salinity boost during production. In the 2019 Australian Journal of Grape and Wine Research study, the authors found an increase of 1.7 times the chloride concentration in must when a red wine was fermented on the skins.

There are many factors that impact not only how much salt is in the wine, but how that salinity is perceived—not only in terms of intensity, but even if that salinity contributes a positive or negative taste. Many of these factors remain unknown and the variables are numerous. Like so many aspects of wine, our current understanding of salinity leaves ample room for research.

Alex Russan, based in Santa Barbara County, California, is the owner-winemaker of Metrick wines. He consults for ¿Por Que No? Selections and previously owned sherry label and Spanish import company Alexander Jules. He writes about enology, viticulture, and tasting and has a background in specialty coffee, botany, and philosophy.

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