Sulfites in wine: friend or foe?
One of the things I hear frequently from people who find out I’m a technical guy for winemaking is, “I’m allergic to the sulfite in wine. What can I do?” My heart sinks when I hear this. Sulfite allergy is such an all-pervasive myth that it seems like an endless tide of misinformation to stand against, and even some of the people who should know better (like wine educators and salesfolk) sometimes give the impression that there’s some validity to the idea that sulfite is in some way contributory to allergic responses or headaches from wine. Because they don't. They literally can't.
A few quick facts about sulfite before we address the allergy issue. What is Sulfite?
Sulfite is the name given to a stable salt of elemental sulfur, usually Potassium Metabisulphite. It works by releasing free sulfur dioxide (FSO2), which inhibits yeast, mold and bacteria, and scavenges oxygen out of the wine. It is added to unfermented grape juice to suppress indigenous yeast and spoilage bacteria, and directly to wine after fermentation, to prevent oxidation. Oxidation in wine follows the same pattern in an apple slice exposed to air—the wine browns and takes on a flat ‘cardboard’ taste. Sulfite goes through a redox reaction with oxygen, preventing browning and flavor loss. Sulfite is a recognized food additive. Its use is governed by Federal legislation.
Where can Sulfites be found?
All wine contains sulfite; even wines labeled ‘no sulfite added’. All wine produces sulfite naturally during fermentation, up to a level of about 10-PPM. Even with no addition of outside sulfite, wine always contains it—it cannot be removed.
The legally allowable amount of sulfite is 70-PPM FSO2 in dry table wine.
Nearly all dried fruit and meat contains sulfite. Raisins have up to 1250 PPM.
Bacon, orange juice, potato chips, cider, candied fruits, sausages, and even pancake syrups contain sulfite: often at levels vastly higher than those found in wine.
The human body produces its own sulfite as a by-product of metabolic activity–that’s right, you contain sulfite.
The truth about Sulfite
Fortunately for my continued work as a wine guy, I realized that if I didn’t give the good information, it was my own darn fault if people didn’t learn the truth. To whit: human beings can’t be ‘allergic’ to sulfite. An allergy is an inappropriate immune-system response. Sufferers have excessively active white blood cells: when an allergen binds to the mast cells or basophils they produce antibodies that cause an inflammatory response, which can range from mildly annoying to lethal.
Sulfite, a stable salt of elemental sulfur cannot provoke this immune response–it just does not work this way.
Common (false) ideas about sulfite:
What about sulfa drugs? Lots of people are allergic to those. The class of drugs known as ‘Sulfa’ (actual name, ‘Sulfonamides’) don’t contain any sulfur in any form. The two aren’t chemically related. It’s like claiming to be allergic to pencils because you are also allergic to penicillin.
What about asthma? Sulfites trigger asthma. Lots of things trigger asthma that are not allergens. When very high concentrations of sulfite dust or the vapor from a liquid solution comes in contact with mucous membranes (like the alveoli in your lungs) the moisture in them combines to make sulfuric acid. That makes everyone’s lungs cramp, not just asthmatics, but it’s not an allergy.
I’m allergic to sulfite. You’re not an allergist! No, I’m not. But you’re not allergic to sulfite either. You may be very sensitive to it (as I am–surprise!) but that’s a very different thing.
I’m not a doctor/allergist/scientist, just a wine-guy. I wouldn’t possibly comment on this issue without a major backstop. My source is Dr. Janice Joneja, a pretty darn smart person and a renowned expert on allergies. She’s far more adamant about the allergic potential of sulfite in winemaking than I’ll ever be (in addition, she’s extremely patient and generous with her time towards geeky wine tech guys–thanks Dr. J.)
So, what does cause people’s problems with wine? Shunting aside the obvious (drinking too much wine) the biggest contributor to negative response to wine consumption is bio-amines. Plants produce these as natural defenses against predators, and they work. In humans they provoke immune response, and are the reason why people take antihistamines.
Fully ripened grapes don’t contain massive amounts of bioamines, and the yeast that causes the fermentation process doesn’t add significant quantities of them either. The bioamines in wine generally come from a secondary fermentation treatment known as ‘malolactic fermentation‘, or MLF. MLF is caused when a bacteria (typically a cultured one added to commercial wines) consumes the malic acid in the must and converts it into lactic acid. This can be desirable for two reasons: first, malic acid is pretty harsh, tasting like green apples, while lactic acid is softer and easier on the palate.
Second, a by-product of MLF is the compound diacetyl, which lends a buttery or melted butter aroma to the wine. This is so strong that commercially synthesized diacetyl is the flavor ingredient used in microwave popcorn (which is why they call it ‘buttery’ rather than ‘buttered’). MLF is normally executed on red wines, some Chardonnays and very few other whites. Unfortunately the bacteria also produces large amounts of bioamines, and these are probably the source for most people’s allergic response to wine–since only a few white wines get it, it’s the source of the ‘red wine headache’ trope–which is particularly amusing since white wines usually contain higher levels of sulfite than reds, yet it’s reds that get blamed, because of the bioamines.