Sulfur dioxide is added to dried fruit primarily to preserve color and prevent spoilage. Without it, dried apricots would turn from bright orange to dark brown within weeks, and many fruits would develop off-flavors or lose key nutrients during storage. It’s one of the oldest food preservation techniques still in wide use, and while it’s safe for most people, it poses real risks for a small percentage of the population.
How Sulfur Dioxide Preserves Dried Fruit
When fruit is sliced and exposed to air, enzymes trigger a browning reaction, the same process that turns a cut apple brown on your counter. Sulfur dioxide halts this reaction by blocking the enzymes responsible. It also acts as an antioxidant, slowing the breakdown of the fruit’s natural pigments and flavors over months of storage.
Beyond cosmetics, sulfur dioxide inhibits the growth of mold, yeast, and bacteria on the fruit’s surface. Dried fruit still contains enough residual moisture to support microbial growth, especially in warm or humid conditions. The sulfur dioxide creates a chemical environment that keeps these organisms in check, extending shelf life significantly. Sulfured dried apricots, for instance, can last a year or more on the shelf while retaining a bright golden-yellow color. Unsulfured versions darken to brown or nearly black and have a noticeably shorter window before quality declines.
There’s also a nutritional angle. Sulfur dioxide has a reducing (antioxidant) character that helps protect vitamins A and C during drying and storage. Early research on dried peaches found that the sulfites formed during treatment shielded vitamin C from breaking down, likely because of the acidic environment they create and their ability to neutralize oxygen before it degrades sensitive nutrients. The tradeoff is that sulfur dioxide destroys thiamine (vitamin B1), so sulfured dried fruit is not a reliable source of that particular nutrient.
What Sulfured vs. Unsulfured Fruit Looks Like
The visual difference is dramatic. Sulfured dried apricots maintain that familiar bright, almost candy-like orange. Unsulfured apricots look completely different: deep brown, sometimes nearly black, with a chewier, denser texture. The taste shifts too. Unsulfured fruit tends to have a more concentrated, caramelized sweetness because the browning reactions that sulfur dioxide prevents actually develop new flavor compounds.
Light-colored fruits show the biggest contrast. Apricots, pears, peaches, and apple rings are almost always sulfured in conventional production because consumers associate the pale, vibrant color with freshness. Darker fruits like raisins, prunes, and dates may or may not be treated, since their natural color masks much of the browning.
Who Needs to Avoid It
For most people, the sulfur dioxide in dried fruit is harmless. Your body breaks sulfites down efficiently using a naturally occurring enzyme, and the amounts in food are well within safe limits. But for a subset of people with asthma, sulfites are a genuine trigger. Studies consistently report that 3 to 10% of adult asthmatics experience adverse reactions to sulfite additives, ranging from mild wheezing to severe, potentially life-threatening breathing difficulties.
The mechanism isn’t fully understood, but inhaling sulfur dioxide gas released from food (or absorbing sulfites through digestion) can cause the airways to constrict in sensitive individuals. People with severe or poorly controlled asthma face the highest risk. Sulfite sensitivity outside of asthma is much rarer, though some people report headaches, skin flushing, or digestive discomfort.
If you have asthma and have never had a reaction to dried fruit or wine, you’re likely not sulfite-sensitive. But if you’ve noticed breathing issues after eating dried fruit, sulfites are worth investigating with your doctor.
Labeling Rules in the U.S.
The FDA requires any food containing 10 parts per million (ppm) or more of sulfites to declare them on the label. At that threshold, sulfites are considered “detectable,” and a food sold without proper labeling is legally misbranded. This is why you’ll see “contains sulfites” or “sulfur dioxide” in the ingredients list on most packages of dried apricots, mango, and similar products.
Below 10 ppm, labeling is not required, because the amount is considered incidental and unlikely to cause a reaction even in sensitive individuals. Foods that pick up trace sulfites from another ingredient during manufacturing (rather than having sulfites added directly) also fall below this threshold in most cases. Imported dried fruit that contains undeclared sulfites above 10 ppm can be detained at the border without physical examination under FDA import alerts.
If you’re actively avoiding sulfites, check the ingredient list rather than relying on front-of-package claims. Products marketed as “natural” may still contain sulfites if they fall below the declaration threshold. For certainty, look for packaging that specifically says “unsulfured” or “no sulfites added.”
Choosing Between Sulfured and Unsulfured
Your choice comes down to priorities. Sulfured dried fruit looks more appealing, lasts longer, and retains more vitamin C and vitamin A. Unsulfured dried fruit avoids a common allergen trigger, preserves thiamine, and appeals to people minimizing food additives. Nutritionally, neither option is dramatically superior for someone without sulfite sensitivity.
If you buy unsulfured dried fruit, store it in a cool, dark place in an airtight container. It will darken further over time regardless, but proper storage slows quality loss. Refrigeration or freezing extends its usable life by several months. Sulfured varieties are more forgiving with storage but should still be sealed tightly once opened to prevent the sulfur dioxide from off-gassing, which reduces its protective effect over time.