The Short Answer: Naturally Occurring, Not Added
Contrary to a common misconception, winemakers do not add nitrates ($NO{3}$) as a preservative during the vinification process. The presence of nitrates in white wine, or any wine, is due to the natural absorption of nitrogen-based compounds by the grapevines from the soil and water. The levels of these naturally occurring compounds in wine are typically very low, often a small fraction of what is found in many everyday vegetables. When it comes to wine preservation, the compound to be aware of is sulfur dioxide ($SO{2}$), or sulfites, which are added to inhibit microbial growth and prevent oxidation. This confusion between nitrates and sulfites is a primary source of misinformation for many consumers.
Unpacking the Science: Nitrates vs. Sulfites
To truly understand the makeup of wine, it is crucial to distinguish between nitrates and sulfites, two very different compounds often conflated by the public.
Nitrates are naturally occurring chemical units composed of nitrogen and oxygen. They are a fundamental part of the soil ecosystem, and grapevines, like other plants, absorb them as a vital nutrient for growth. Once in the plant, these compounds play a role in the vine's metabolic processes. The trace amounts that may end up in the finished wine are simply a byproduct of this natural cycle. For most people, the levels are not significant enough to pose a health risk.
Sulfites, on the other hand, are a different story. They are intentionally added to most commercial wines by winemakers to act as an antioxidant and antimicrobial agent. This prevents the wine from spoiling and helps maintain its flavor and color over time. Sulfites are also naturally produced in small quantities during fermentation. A key distinction is that white wines typically contain more added sulfites than red wines. This is because red wine gets natural preservative qualities from its tannins, which are extracted from the grape skins during fermentation. White wines, which have no skin contact, require more protection from spoilage.
Comparison Table: Nitrates vs. Sulfites in Wine
| Feature | Nitrates ($NO_{3}$) | Sulfites ($SO_{2}$) |
|---|---|---|
| Source | Naturally occurring in soil; absorbed by vines. | Added by winemakers; also a natural byproduct of fermentation. |
| Purpose | A nutrient for grapevine growth. | Preservative, antioxidant, and antimicrobial agent. |
| Addition | Not intentionally added by winemakers. | Routinely added to almost all wines. |
| Concentration | Trace amounts, typically very low. | Up to 350 ppm in U.S. wines, generally higher in white than red. |
| Associated Concerns | Potential link to migraines in some sensitive individuals. | Allergic-type reactions in sensitive people, particularly asthmatics. |
The Source of Nitrates in Grapes
Grapevine nutrition is a complex process. The nitrogen absorbed by the roots from the soil is essential for the plant's metabolism. The amount of nitrates in grapes can vary based on several factors, including the type of soil, climate, and viticultural practices, such as fertilizer use. For example, vineyards that use nitrate-based fertilizers or are located in regions with high soil nitrogen levels may produce grapes with slightly higher natural nitrate concentrations. However, winemakers and viticulturists work to manage nitrogen levels carefully, as both deficiency and excess can negatively impact grape quality. The ultimate goal is a balanced fruit composition, not high nitrate levels.
Factors Influencing Natural Nitrate Levels in Grapes:
- Soil Composition: Nitrogen content varies significantly across different vineyard soils, which directly impacts vine uptake.
- Fertilization Practices: The use of nitrogen-rich fertilizers can increase soil nitrate levels, though many modern viticultural practices aim for balance rather than excess.
- Rainfall and Irrigation: Water moves nitrates through the soil, so rainfall and irrigation schedules play a role in how much is available for absorption.
- Cover Crops: Some vineyards use cover crops between vine rows to manage nutrients, which can affect the nitrogen cycle in the soil.
- Grape Variety: Different grape varieties may have slightly different uptake rates for soil nutrients, leading to minor variations in natural nitrate levels.
Nitrate Levels in White Wine Compared to Other Foods
If you are concerned about your dietary intake of nitrates, focusing on white wine is largely misdirected. Numerous studies have shown that the nitrate levels found in many common vegetables vastly outweigh the trace amounts present in wine. A survey by Food Standards Australia New Zealand (FSANZ) highlighted this by comparing levels in various foods, finding that white wine contained around 10mg/kg of nitrites, while foods like spinach and celery had concentrations well over 1000mg/kg. This perspective is important for understanding that wine is not a major dietary source of nitrates.
Examples of Foods with High Nitrate Levels:
- Spinach
- Celery
- Lettuce
- Beetroot
- Radish
- Parsley
- Processed meats (where nitrates are added for preservation)
The Health Concerns: Decoding the Myths
One of the most persistent myths surrounding wine is that nitrates cause headaches. A 2016 study found a correlation between certain oral bacteria that convert nitrates into nitrites and migraines in some individuals, suggesting a potential link. However, the researchers noted that correlation does not equal causation, and the link needs further investigation. The more widely understood trigger for reactions is actually sulfites, to which asthmatics, in particular, may be sensitive. Other factors, such as histamines, tannins, and alcohol itself, are also known culprits for wine-related headaches and discomfort. For the majority of people, the minimal amount of naturally occurring nitrates in white wine is not a concern, and the health benefits of consuming fruits and vegetables with higher natural nitrate levels far outweigh any minimal risk associated with wine.
Conclusion
In conclusion, white wine does contain trace amounts of nitrates, but this is a natural consequence of the grapevine's nutrient absorption from the soil. Winemakers do not intentionally add nitrates for preservation; instead, they add sulfites, which serve a different purpose and are responsible for many of the sensitivities people experience with wine. The levels of natural nitrates in wine are insignificant when compared to many common, healthy vegetables. For most consumers, the presence of these trace natural compounds is not a cause for concern. If you experience adverse reactions after drinking wine, it is far more likely that other factors, such as added sulfites or histamines, are the cause rather than naturally occurring nitrates. Enjoying your white wine in moderation is the best approach.
Optional outbound link
For more detailed information on vineyard management and the role of nitrogen in grape growing, visit the research resources at the Australian Wine Research Institute: awri.com.au/wp-content/uploads/1_nutrition_nitrogen_fertilisation.pdf.
