Sulfites in wine; what are they, and are they bad for you?

Sulfites in wine: What are they, and are they bad for you?

There are three commonly discussed sulfur-related compounds in wine, but they are not all considered “sulfites”.

Sulfur powder is an elemental powder dusted on vines, which protects against Botrytis and other moulds. This form of sulfur is not a sulfite and is not present in finished wine if properly handled. However, if residues remain on grapes at harvest, they can contribute to unwanted sulfur compounds during fermentation (like H₂S)

Sulfur dioxide (SO₂) is a true “sulfite”; it is commonly added during winemaking in various manufactured forms, but it is also naturally occurring in small amounts as a byproduct of fermentation.

SO₂ additives serve as antioxidants, antimicrobials and preservatives and are entirely different from sulfur powder used in the vineyard. These sulfiting agents are produced by burning fossil fuels and smelting mineral ores that contain sulfur and come in various forms, including tablets, gas, liquid and powders.

Sulfiting additives are powerful antimicrobials used to suppress the naturally present yeasts and bacteria in wine, allowing the winemaker to inoculate with lab-bought strains instead.

Sulfites also protect wine from oxygen and kill enzymes responsible for the browning of grape juice. Essentially, sulfites used in conventional winemaking eliminate microbial risks while enabling a consistent and chosen wine style.

Low- or no-addition producers may avoid sulfites altogether. However, many use a small, final dose of SO₂ at bottling to stabilise the wine for shipping or aging, without disrupting the wine’s character.

Hydrogen sulfide (H₂S) is a different sulfur compound, typically formed in trace amounts by yeast under stress. It's responsible for the "rotten egg" smell in wine when present, and it's not desirable. Grapes produce different formations of a whole group of sulfur compounds called “thiols” or “mercaptans”. Many of these compounds are undesirable, producing aromas reminiscent of burnt rubber, matches, or rotten eggs. However, at low levels, some of these compounds are attractive and even attributed to “mineral” aromas and flavours.

For example, the “chalkiness” of Chablis is largely a result of hydrogen sulfide (H₂S). Grapefruit, coffee and chocolate are other common aromas and flavours resulting from thiols. These sulfides are generally controlled naturally during fermentation; however, if they become excessive, intervention is typically achieved through micro-oxygenation.

Humans can detect sulphur compounds of this type at low levels, with concentrations as low as parts per billion detected. The natural gas in your home has a distinct smell, which is not naturally occurring. A mercaptan is added in small amounts so that if gas is left on, the smell is detected.

Sauvignon Blanc’s extreme flavour is a perfect example of the effects that naturally occurring sulfur compounds have on wine; the pronounced flavour is a result of the compound 3-mercaptohexanol.

Interestingly, there is virtually none of this compound present in the actual grape. A set of complex steps produces 3-mercaptohexanol:

It begins with fruit damage at harvest(machine-harvested grapes produce up to 20 times as much of this compound as hand-harvested grapes). The broken berries initiate an oxidation reaction, which is then followed by lipid oxidation. This reaction subsequently reacts with sulfites and/or glutathione, setting the stage for the formation of a modified 3-mercaptohexanol. At this point, 3-mercaptohexanol has no aroma until fermentation begins. These steps have all occurred in the field, from picking the fruit to placing the fruit in the bin, before the grapes have even reached the winery.

This naturally occurring process captures the complicated science behind winemaking. Many factors which determine the quality and character of wine are invisible to the naked eye.

Some varieties, such as Syrah, have specific aromas derived from a sulphur-containing compound called Dimethyl Sulphide (DMS). DMS can give aromas of coffee, blackberry, and hay. These compounds are all very volatile; if levels are too high, they create undesirable effects on flavours and aromas.

Conventional wine producers can remove the risk of undesirable traits by heavily sulfiting at all stages of winemaking and controlling fermentation with lab-bought yeast strains, among other measures.

However, when a wine is subjected to excessive SO₂ additions, wine can lose its liveliness and depth, rendering it somewhat “flat”.

The History of Sulfites

While dialogue exists regarding the use of sulfites since Roman times, some research rejects this narrative. Dr. Patrick E. McGovern, Scientific Director of the Biomolecular Archaeology Project for Cuisine, Fermented Beverages, and Health at the University of Pennsylvania Museum in Philadelphia, discusses his research on sulfites in his book, Ancient Wine: The Search for the Origins of Viniculture (2006). His extensive research on the antiquity of wine reveals no evidence that sulfur was used in wine preservation until the end of the 18th century. At this time, Dutch traders introduced the practice of burning sulfur wicks in wine barrels for sanitization and to stabilize the wine for transport. Sulfur used back then was elemental, a different story compared to the forms of sulfur we see today.

Introduced as a byproduct of the petrochemical industry in the 1900s, the majority of sulfiting agents are now produced by burning fossil fuels and smelting mineral ores that contain sulphur.

Today, it is common for sulfites to be added in every step of winemaking in the form of a gas, powder, liquid, or tablet.

Wine labels are required to list “contains sulfites” if the wine contains more than 10mg/L of sulfites(inclusive of naturally occurring H₂S and added SO₂). This means that if a producer adds no sulfites at all, but naturally occurring H2S breaches 10 mg/l( 6-40mg/L is common), this wine must now be labelled just as a producer ADDING up to 350mg/L of the petrochemical byproduct, SO₂.

This is just one example of wine labelling laws which leave wine drinkers in the dark.

Are sulfites bad for you?

SO₂ is utilized to destroy microbial life. SO₂ enters our bodies when we consume products containing SO₂, causing damage to our microbiome. Additionally, microbes naturally present in wines can be beneficial to our vitality, like other fermented goods such as sauerkraut and kombucha. Research continues to mount on the importance of microbiota for our health and the consequences of its absence, which are associated with disease.

Research into the effects of sulfite concentrations considered safe for ingestion has revealed that even at these levels, damage is caused to essential bacteria in our gut, and this damage is linked to disease.

“Sulfites and other preservatives are considered food additives to limit bacterial contamination and are generally regarded as safe for consumption by governmental regulatory agencies at concentrations up to 5000 parts per million(ppm). Consumption of bactericidal and bacteriostatic drugs have been shown to damage beneficial bacteria in the human gut, and this damage has been associated with several diseases.” (Irwin et al. 2017)

Wine is not alone. Many food and beverage items, such as dried fruits, tea, french fries, cheese, syrups, meats, and others, receive sulfite additions. Could this mean that if a person is drinking wine containing up to the legal limit of 350mg/L of SO₂, as well as consuming the average North American diet, the accumulation of sulfites ingested could exceed safe limits? Similar concerns are also prevalent in our food industry, with some producers opting for production measures that limit sulfite additions.

Are sulfites to blame for headaches? Sulfites can’t be singled out; producers who are liberal with sulfites, are often so with many more unnatural additives. Wine headaches could be the result of several things or a combination, particularly if you are drinking heavily manipulated wines. Conventional wines can be laden with additives; over 70 additives are approved in the US. High residual sugar(RS) levels could also be to blame, especially with some conventional producers adding straight sugar to their wines.

Headaches are not the only symptom of a sulfite sensitivity; others include: hives, itchiness, swelling (face, lips, tongue), redness, upset stomach, vomiting, nausea, painful cramps, vomiting, flushing, dizziness, low blood pressure, trouble breathing, coughing, chest pain or tightness, throat tightness, hoarse voice, nasal congestion, hay fever-like symptoms (runny, itchy nose, watery eyes, sneezing), trouble swallowing, paler than normal skin colour/blue colour, weak pulse, fainting, dizziness or lightheadedness, shock, anxiety, sense of doom (the feeling that something bad is about to happen), headache, uterine cramps, and a metallic taste in the mouth.

There are other theories for what causes wine headaches besides drinking too much-that’s called a hangover. Alternate theories include sensitivities to histamines (naturally occurring in fermented beverages), tannins, alcohols, yeasts, and tyramines (migraine-associated enzymes found in various foods).

Wine labels are flawed.

Sulfites in wine are not an easy topic to unpack, but they do highlight the importance for wine drinkers to take the time to investigate the wine they're drinking to make informed decisions. Besides SO₂, there are numerous questionable additives in conventional wine that the label will not disclose.

References

Waterhouse, A., Sacks, G., Jeffrey, D. (2016). Understanding Wine Chemistry. John Wiley & Sons, 2016

McGovern, P.E. (2003) Ancient Wine: The Search for the Origins of Viniculture. Princeton, New Jersey, US: Princeton University Press

PubMed. Irwin, S. Fisher, P., Graham, E., Malek, A., Robidoux, A. (2017). Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food. [Online]. Available from: https://pubmed.ncbi.nlm.nih.gov/29045472/. [Accessed: August 2020]

GuildSomm (March 2018) Wine Chemistry.[Online]. Available from: https://www.guildsomm.com/public_content/features/podcasts/b/guild_podcasts/posts/wine-chemistry. [Accessed: August 2020]

Legeron, I. (Editor: Caroline West).(2017). Natural Wine An Introduction to Organic and Biodynamic Wines Made Naturally. 2nd Edition. London, England/New York, NY, US: CICO Books an Imprint of Ryland Peters & Small Ltd

Food Allergy Canada. (2020) Sulphites. [Online]. Available from: https://foodallergycanada.ca/food-allergy-basics/food-allergies-101/what-are-food-allergies/sulphites/. [Accessed: September 2020]

WebMD. (August 18, 2019). Asthma and Sulfites Allergies. [Online]. Available from: https://www.webmd.com/asthma/asthma-and-sulfites-allergies. [Accessed: September 2020]

PubMed. M. Hasan Mohajeri, Robert J. M. Brummer, Robert A. Rastall, Rinse K. Weersma, Hermie J. M. Harmsen, Marijke Faas, and Manfred Eggersdorfer. (2018). The role of the microbiome for human health: from basic science to clinical applications. [Online]. Available from:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962619/. [Accessed: August 2020]