Sulphites (or sulfites, if you are American) are already an allergen of their own – so much so that in Canada they are considered a major allergen that must be reported on food products. Sulphites are a regular ingredient in wine production, so much so that finding wine without sulphites is uncommon. I heard a little while ago about people with glycol allergies being wary of dried fruits and vegetables produced using the sulphite process, and wanted to investigate further.
Fruits and vegetables can be dried via a number of different methods. Many add sugar to fruit. Dried fruit with no added sugar can actually be three to six times more expensive than frozen fruit, even for manufacturers making use of this dried fruit to make other products. Sulphites are commonly added to maintain the original colour of the fruit – brown and shrivelled is more what sulphite-free dried fruits and vegetables should look like. Most produce is washed in chlorinated water before drying, but the chlorine should readily evaporate during the drying process. Food nutrition after drying has not been thoroughly studied at this time, but the methods of drying are quite diverse:
Freeze drying – No ingredients need to be added for this drying process. First, the produce is frozen. Next, it is placed in a vacuum chamber under low heat. The ice crystals in the food change directly from a solid to a gas, in the same way that ice cubes in your freezer slowly get smaller and smaller even though they’re not melting: Sublimation. The vacuum outside the food pulls this water vapour out of the food. This is one of the most costly methods of drying produce. The result is a piece of dried produce that usually maintains the original look and structure of the fresh produce, but very crunchy and dry. Dried produce manufactured using this method can be so dry that it pulls moisture from the air when left in an unsealed package and becomes more chewy.
Infused – A concentrated sugar solution is added to the fruit and the mixture is heated until the sugar moves into the fruit and the water evaporates. Sugar solution can be high fructose corn syrup.
Sun-dried – Fruits can be sun dried easily, but vegetables that are high in acid and sugar are usually the only ones that can be sun-dried. They start by being washed, cut or cracked in some way to expose the highest-moisture part of the produce to the air, and then laid out on trays in the sun until dried.
Drum dried – Often needs a carrier to be added to prevent sticking of the produce to the drum. A tumbling motion characterizes this method, where warm, dry air carries away moisture from the produce.
Air dried of tunnel-dried – Produce is set onto a screen or other porous platform and dried with the application of heat and good dry air currents.
Drying method really doesn’t seem to have any direct impact on what chemicals or extra ingredients are added in most cases; it all comes down to the manufacturer’s choice.
Sulphuring and sulphite dips (the sulphite process) are not the same thing. To sulphur produce, sulphur is burnt in an closed box, and the fumes penetrate the produce to prevent spoilage. This is a very old process. Sulphite dips are much faster, and involve a vat containing dissolved sodium bisulphite, sodium sulphite, or sodium meta-bisulphite. Produce is dipped into the vat and then dried by whatever method chosen. On packaging, this will be labelled as sulphur dioxide (due to the chemical processes that occur, the chemical changes). According to the FDA, only products containing more than 10 ppm, or 10 mg/L, are required to list sulphur dioxide on the label (in the US).
There are other methods of preserving colour in produce, but these are not as effective long-term, and are thus less used. Ascorbic acid (vitamin C) and sugar are both common preservatives. Ascorbic acid by itself is the most effective of these two, but ascorbic acid mixed with sugar, fruit juices that are high in ascorbic acid, honey, and sugar solutions are all valid options. Steam blanching is another method, using only water, that colour can be preserved, though flavour and texture can change.
Vegetables are more often just blanched by water or steam.
The most important thing I learned for sulphite allergy sufferers is that organic dried fruits do not contain sulphites, at least in North America and Australia.
What other ingredients are in dried produce?
Aside from the above-mentioned sugars, ascorbic acid, fruit juices, honey, sulphur, sulphites, and chlorinated water used to wash, some fruits, like raisins and berries, have a thin coating a vegetable oil applied to prevent them from sticking together. Any dried fruit or vegetable that is NOT organic can also contain pesticides and herbicides. I cannot find a concrete source of glycol in the drying or preserving process, though I am sure some manufacturers could find a reason to add it if desired.
So what in dried fruit might cause glycol allergy sufferers problems?
Remember, dried fruit is fruit that has most of the water removed. Drying fruit does not remove its sugars or fibre. One single dried apricot contains all of the sugar and non-evaporating chemicals and plant structure of an entire apricot (plus any added sugars and chemicals). This means that if you eat ten dried apricots you are eating the equivalent chemicals of ten whole apricots. Even if one apricot’s chemical load didn’t bother you, ten might. I mentioned before about pesticides and herbicides being a possible source of glycol in non-organic produce, and this effect is amplified in dried produce because we eat more of it.
From everything I can find, eating organic dried produce should eliminate any possible issues with either a sulphite or a glycol allergy, though it is always important to thoroughly read labels and be aware of their limitations. If you are really concerned about glycol or sulphites in your dried produce, the best way to ensure safety is to buy organic and dry it yourself. The links below should help with that.