I’m not a doctor, but I feel compelled once again to elucidate the facts vs. fiction regarding the physiological and neurological effects of sulfites based on my meta-survey of published, peer-reviewed scientific research—the kind backed by hard data to prove or disprove claims.

What are sulfites?

The term “sulfites” refers to salts comprising one of the several sulfite ions (e.g. bisulfite [HSO3¯], sulfite [SO3²¯], metabisulfite [S2O5²¯]), or more precisely, sulfur dioxide (SO2) ions. Sodium bisulfite and potassium metabisulfite are examples of sulfite salts; the latter is the most common form used in winemaking.

Sulfites and SO2 are very effective antioxidants protecting wine from the destructive effects of oxygen, and also act as antimicrobial agents preventing wine spoilage from rogue yeasts and bacteria.

Although sulfites have been used in winemaking since the days of the Romans, the growing public awareness of the use of sulfites in wines—mainly from those alarming US General Surgeon warnings on labels—and the trend towards more “natural” (whatever that means) and healthier foods have turned sulfites into an evil of sorts. Red wines and sulfites are unequivocally blamed for all sorts of ailments, from headaches and migraines to upset stomachs. Note that the General Surgeon warning is only required for wine containing more than 10 mg/L (ppm) of total sulfur dioxide (SO2). But all wines exceed this threshold, with or without sulfite additions, since cultured winemaking yeasts naturally generate in the order of 10 mg/L or more of SO2 during alcoholic fermentation. Some indigenous yeast used in “natural” winemaking, or what some call minimalist winemaking, can produce upwards of 100 mg/L of SO2, sometimes more than all sulfite additions put together.

Physiological Effects of Sulfites

Sulfites are critical components of many biological systems. Our body manufactures a small amount of sulfur dioxide during metabolism of amino acids and converts it into harmless sulfates (SO4²¯).

There is ample data to support classifying sulfites as toxicological substances. What is known is that sulfites can trigger respiratory attacks amongst the 1% population of asthma sufferers. Sulfites cause inflammation of mastocytes, or mast cells, that reside in tissues including those in the lungs. The mast cells contain many granules rich in histamine and are released during the inflammation triggering the attack. For this reason, control and disclosure of these additives are warranted. If you are not familiar with the effects, prepare a 10% solution (10 g in 100 mL of water), pour in a bowl and take a tiny sniff—the vapor quickly causes a suffocating reaction within the nasal passage and pain up to the sinuses.

But do sulfites in red wine really cause headaches and migraines? The literature is littered with anecdotal evidence that sulfites are the culprits. My own informal survey from years of asking the question to those who blame sulfites disproves such claims in one hundred percent of cases. The first question when someone states that they cannot drink red wine as it gives them headaches is, “Do you get headaches after drinking white wine?” The answer is always, “No.” The fact is that whites generally have higher sulfite levels since they are more susceptible to oxidation effects given their much lower levels of protective (antioxidant) polyphenols compared to reds. Polyphenols in reds come mainly from grape skins during the maceration and fermentation phases of red winemaking; whites are not macerated and therefore there is no polyphenol extraction.

Of those surveyed, none of those who ate dried fruits have reported to get headaches, yet, dried fruits are known to contain appreciable amounts of sulfites.

Those Nasty Biogenic Amines

The most common source of headaches and migraines lies in biogenic amines, which include histamine and tyramine, respectively. Amines are organic compounds resulting from the decarboxylation (removal of CO2) of amino acids and are generally characterized by unpleasant odors. Amines are used in a number of applications including medical drugs, such as antihistamines used for treating colds or fever, illicit drugs, such as methamphetamines, and most have physiological and neurological effects and therefore of health concern. Biogenic amines are the product of life processes, such as fermentation, and include butanediamine, better known as putrescine, and pentamethylenediamine, better known as cadaverine, both of which have a very strong, foul smell typical of decayed meat—definitely not desirable compounds in any food or beverage.

Red winemaking most often involves a second fermentation, known as malolactic fermentation, or MLF, which converts the sharper-tasting malic acid into the softer lactic acid. This is accomplished by cultured lactic acid bacteria (LAB), some of which can produce biogenic amines, including histamine and tyramine, or if the MLF is not properly managed. If a specific bottle of red wine is known to cause headaches, with the next bottle, first take antihistamine to establish whether histamines are in fact the problem. Whites are usually not processed for MLF as the by-products do not marry well with the lighter, fruitier style. Full-bodied, barrel-fermented or oak-aged, buttery Chardonnays are common exceptions. And so, Chardonnays and other MLF whites can also be a source of biogenic amines. The effects of these amines are compounded in the presence of alcohol, and so, again, reds tend to be the culprits given their higher alcohol levels. But individuals that possess the digestive enzymes (amine oxidases) that inactivate the biogenic amines will feel no ill effects.

Tannins

Another possibility is tannins—those compounds responsible for the taste of bitterness and sensation of astringency in reds, or as winemakers prefer to say, tannins add to the “mouthfeel.” Tannins are believed to release serotonin—a neurotransmitter found mainly in the gastrointestinal tract but also in the central nervous system. Serotonin dilates and constricts blood vessels in the brain, which can cause headaches and possibly migraines. Serotonin also causes the gut to move faster, which can cause diarrhea.

We can conclude that tannins too can be classified as toxicological, but they aren’t probably by their virtue of being natural. Tannins are naturally synthesized in plants as part of their defense mechanisms.

Are Sulfites Bad?

Sulfites are suffering a bad rap only because they are not “natural.” Sure, sulfites are not really good if we could do away with them, but they are not necessarily bad either when used judiciously. But consumer perception is reality—sulfites are bad.

Winemakers need to deal with this one way or another, but no other alternative has proven anywhere as effective as sulfites at protecting wine. I strongly believe that winemakers can reduce the use of sulfites by getting into a minimalist mindset, but I don’t believe that zero sulfites is the solution—not yet given the winemaker’s toolset. Vinegrowing and winemaking conditions are rarely perfect to completely eliminate sulfites—a minimum amount is always required. Until some new solution proves more effective and “healthier,” sulfites are here to stay. Just ask the Romans.