Increased Salinity Levels in Mexican Wine: Correlations and Possible Causations

When I think of Mexico, I tend to think Tequila and Margaritas, and not so much wine. However, Mexico happens to have one of the oldest wine industries in the West. Starting way back in the 1500s after the Spanish invaded, Mexican wine had started to outsell Spanish wine as a result of which around 1700 the King of Spain put a ban on all Mexican wine (except for use in the church), which pretty much put growth of the Mexican wine industry to a halt. Things started to revive again in the late 1800s when the first commercial winery was established (Bodegas de Santo Tomas).

For more information about the history of the Mexican wine industry, check out this informative post by VineTalk that was written last year (click to read).

I’ve never actually had a Mexican wine before, as last time I was in Mexico I made it a point to procure all the Tequila (mostly in the form of Margaritas) I could get my mitts on while I was there. The majority of the wine in Mexico is produced

The Academic Wino enjoying a book ("Reading Between the Vines") on a beach in sunny Mexico! Image Copyright RYeamans 2013

The Academic Wino enjoying a book (“Reading Between the Vines”) on a beach in sunny Mexico! Image Copyright RYeamans 2013

in the Baja region of the country where the climate tends to be very similar to that of the Napa Valley in California. Unlike Napa wines, however, wines from Mexico are notable for having a salty character to them, which is often off-putting to consumers. In the Baja region of Mexico, they’ve been having problems in recent years with water availability and a general decrease in the quality of what water is there. As a result of this, salinity (salt) levels in the ground water have significantly increased in this area, though it’s unknown at this point if this increase in salt levels in the water is responsible for the “saltiness” in Mexican wines or not.

Grapes are very sensitive to salt, and it has been shown that biomass and grape yield decrease when the salinity of the irrigation water increases. Physiologically, the excess salt results in increased closure of the stomata on the grape leaves, which in turn cause reduction in photosynthesis and growth. Entering the plant through the roots, the salt ions can accumulate all over the plant, transferred to leaves and berries by way of the xylem and phloem transport systems (sort of like our blood moving ions around in our bodies).

Sodium is a required ion for plant growth, however, the amount necessary is only about 0.5% of the dry weight of the plant. Potassium, on the other hand, is another ion that is required for plant growth, with the amounts required in plants slightly higher than that of sodium (3% of the dry weight). Maintaining a specific ion balance in the plant is critical for successful growth, reproduction, and survival, and any disruption in that balance could be cause for trouble for the plant.

Mexico isn’t the only wine region that struggles with high salinity in the irrigation water. Texas has had some grapevine die-offs due to high salinity in the groundwater, while at times some regions in South Australia have also struggled with higher salinity levels in their irrigation water. It is possible that other wine regions in the future may begin to see problems

Photo By Marrovi (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or FAL], via Wikimedia Commons

Photo By Marrovi (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or FAL], via Wikimedia Commons

with salt or other ion imbalances in their irrigation water, as climate change alters the precipitation patterns around the globe. Of course, this is just conjecture on my part, but I would think with those areas seeing decreased precipitation and increased drought over time, the ion balance will be out of whack thus potentially increasing the salt and other ion levels in the water and possibly creating problems with grapevine growth and wine quality issues.

The purpose of the short study presented today was to examine the concentrations of different ions: specifically calcium (Ca2+), magnesium (Mg2+), potassium (K+), and sodium (Na+) in wines from Mexico and to compare them to levels of the same ions in wines from other regions around the world.

Methods

Wines used were from Mexico and other countries all over the world, most of which had been part of a competition organized by the University of Baja California (Ensenada Tierra de Vino) between 2009 and 2012. In total, there were 204 white wines and 725 red wines, all between the vintages of 1989 and 2011.

Ca2+, Mg2+, K+, and Na+ ions were analyzed and measured using atomic absorption spectroscopy.

Results

• Ion concentrations were significantly between red and white wines and also between Mexican wines and wines from other parts of the world (i.e. “international” wines).
• Average Ca2+, Mg2+, K+, and Na+ levels were significantly higher in Mexican red wines than international red wines.
• Only average Na+ levels were significantly higher in Mexican white wines compared with international white wines.
• Average K+ concentrations were significantly higher in all red wines compared with white wines, while Ca2+, Mg2+, and Na+ were statistically similar between red and white wines.
• The lowest Na+ (sodium) levels were found in white wines from the following regions: Chile, France, Italy, and Spain, while the lowest Na+ levels in red wines were from Chile and France.
• The highest Na+ levels were found in white wines from Mexico, with the highest level reaching 757.4 mg/L, and similarly Na+ levels in red wines were also highest in Mexican wines, with the highest levels reaching 1151.9 mg/L.
• The lowest Ca2+ (calcium) levels were found in red wines from Spain and the United States.
• The highest Ca2+ levels were found in red wines from Italy.
• The lowest Mg2+ (magnesium) levels were found in wines from France.
• The highest Mg2+ levels were found in wines from Mexico and Italy.
• The lowest K+ (potassium) levels were found in wines from France.
• The highest K+ levels were found in wines from Mexico.
• For varietal wines, there were significant differences in ion concentrations between Mexican and other international wines.
o        For Cabernet Sauvignon, all four ions were significantly higher in Mexican wines compared with all other international wines.
o        Na+ levels in Cabernet Sauvignon were 4 times higher in Mexican wine than international wines.
o        For Tempranillo, Ca2+ and Mg2+ were similar between Mexican and international wines, however K+ and Na+ levels were significantly higher in Mexican wines compared with other international wines.
o        For Merlot, Mg2+, K+, and Na+ levels were significantly higher in Mexican wines compared with other international wines.
o        For Grenache, Zinfandel, and Chardonnay, Ca2+, Mg2+, K+, and Na+ tended to be higher in Mexican wines compared with other international wines, though these values were not statistically significant.

Conclusions

It is clear from this pilot study that sodium and other ion levels are significantly higher in Mexican wines compared with other wines made in other regions of the world. In general, sodium levels were about 2-3 times higher in Mexican wines than wines from other regions of the world. The “saltiness” tasted in Mexican wines may therefore be as a result of these increased ion concentrations.

In terms of potassium, the authors attributed the differences in concentrations between red and white wines as a result of the K+ accumulation in the skins of grapes as they mature on the vine. Since red wines are made with the skins, they are exposed to a higher level of potassium than are white wines, since the skins are removed prior to white winemaking. Some studies have also found that potassium levels increase as maceration time increase (i.e. length of time the skin is in contact with the juice), thus supporting the idea that red wine has higher potassium levels than white wine due to the presence of potassium in the skins of grapes.

Though no sensory analysis was performed on any of these wines, the authors cited previous research stating the wines with higher salt levels scored lower than wines with “normal” salinity levels and were thus perceived as lower quality. According to the authors, the Mexican wines in their study had about the same salinity levels in them than they did in the previous study that they cited.

This was just a “research note”, i.e. not a full-blown study, so I’m not surprised that there are a lot of things that were not done that probably should have been. For example, it wasn’t clear to me that they compared Mexican wines to any of the wine regions that have been known to struggle with salinity problems in the past (i.e. Texas and South Australia), which is a comparison I would have been curious to see.

I would have also liked to have seen a sensory analysis in this study. How do the levels of these ions found correlate with the taste or perceived quality? A quick taste would answer that pretty quickly.

Photo By Tomascastelazo (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Photo By Tomascastelazo (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

I would also be curious to know how salinity levels in wine have changed over the years, and if it could be correlated with environmental changes due to climate change, or if salinity levels in Mexican wine have remained relatively constant throughout time.  It may be hard to find some of the specific environmental data that would be helpful (i.e. salinity levels in irrigation water going back many many years), but as long as there is a good amount of older wines in wine cellars in Mexico, I believe they should be able to at least get an idea of how salinity levels have changed (or not) in the wines themselves over a long period of time.  The wine industry in Mexico started all the way back in the 1500s, so I’m confident someone has some old bottles we could test (maybe not that old though…).

Finally, I would have liked to have seen the researchers test water samples from the regions by which the grapes from the resulting wines were grown. Of course, I suppose it wouldn’t be possible to do that comparison for any year but the current one, since ion levels in the environment aren’t constant over time, but it would at least be a start. For a follow-up study, water ion levels should certainly be tested every year for a number of years, and then compared with the salinity in the grapes as well as the finished wine for those grapes grown in that region. It would be interesting to correlate ions in the water with ions in the wine, and how much does it take to make a big difference in taste?

Overall, this study provides some confirmation that increased sodium levels in wine may be causing a salty taste in the wine (I’m sorry, but can I just say “duh!”?). For winemakers in these regions where salinity levels in the irrigation water are higher, as in Mexico, they may want to consider using appropriate winemaking techniques (i.e. stabilization of tartrate through ion exchange), particularly since it doesn’t appear these practices are being currently utilized in these areas.

Increased salinity levels in the irrigation water is also cause for concern for other plants and wildlife, as well as humans who use the ground water as drinking water (which is a lot of people!). Salt and other ion imbalance can cause survival and growth issues with other crops, plants, and wildlife, and can cause many negative health impacts for humans, including hypertension (high blood pressure). Municipalities may need to consider implementing some sort of treatment plan for the water, as with climate change this issue of decreased precipitation and increases in ion concentrations isn’t going to go away any time soon.

What do you all think of this study and its implications? Please feel free to leave your comments!

Source: Cabello-Pasini, A., Macías-Carranza, V., Siqueiros-Valencia, A., and Huerta-Díaz, M.A. 2013. Concentrations of Calcium, Magnesium, Potassium, and Sodium in Wines from Mexico. American Journal of Enology and Viticulture 64(2): 280-284.

What do you think about this topic?