Lecture 3: Demystifying Your Ingredients - Sulfites

Part 2: Sulfites

Besides fats, ingredient lists contain many other names that you may recognize but not necessary understand.  Many times, these ingredients are preservatives, which are added to increase the shelf-life of your foods.

Today, we will talk about sulfites, a set of closely related chemical preservatives.  This preservative is one that you may consume often.

That is, if you're over 21.

Sulfites

Figure 1.  A common warning on most wine bottles.

So...you're out shopping, and you decide to pickup a bottle of wine for a super-classy, not-student-styled, dinner party.  You stroll over to the wine section and see "contains sulfites" on nearly all the bottles.  It looks like a warning and it sounds bad, but is it?  What is a sulfite anyways?
 
"Contains sulfites" is a catch-all phrase for something that contains sulfur.  Sulfur is a natural byproduct of fermentation, so it's hard to avoid.  In the case of wine, sulfur is usually added in the form of SO2, the preservative known as sulfur dioxide.  Adding this preservative maintains the wine's fresh flavor so that the wine can travel from its winery all the way to your dinner table and taste as intended.  Grapes contain small amounts of sugar, which bacteria like to feast on as the grape breaks down.  Adding a little SO2 makes it very hard for bacteria to survive, and it therefore stops the breakdown.  If the bacterial fermentation process didn't stop, your grapes would turn into vinegar (Spencer 2010).

In general, unless you're allergic to sulfites, the amount of sulfur that's in your food and wine isn't going to hurt you.  You can buy sulfur-free wine, but unless you have a real allergy, that's not necessary.  According to Apartment Therapy, dried fruit contains more sulfites than wine, and red wind has a lower sulfite concentration than white wine and dessert wine (Gorman 2009).  They also mention that any wine with at least 10 parts per million (ppm) of sulfites must be labeled as such.  In other words, sulfites are an important part of keeping your wine fresh, but it's not like you're drinking a glass of sulfur.

Figure 3. Wine in San Gimignano
(Simmons 2012)

In the industrial sense, SO2 could cause some problems. Inhaling SO2 in its gaseous state could cause some lung irritation.  Coming into contact with liquid SO2, which is very cold, would definitely cause some skin problems, perhaps because of the temperature (CCOHS 1997).  Still, both of those events are pretty unlikely, so there's not much need to worry.

Figure 2. Sulfur Dioxide.

If you read our post about fats carefully, you should have noticed how we described carbon as only capable of forming four single bonds.  If you haven't taken organic chemistry, then the sulfur atom (S) in this SO2 diagram might look a little odd to you.  Sulfur is capable of having an expanded octet, which just means it can carry some extra electrons (the dots), which allows them to make more bonds.  So here, sulfur is seen with four bonds (two double bonds) to the oxygen atoms (O) and an additional two, unbonded electrons.

Now that you're had your tidbit of organic chemistry for the day, we'll give you a few more sulfur fun facts:
1) It's spelled "sulphur" in British English, which is simply called "English" if you're from the UK.
2) Sulphur is what makes well water smell like rotten eggs.  Gross!
3) Sulphur is a natural part of life.  It forms disulfide bridges between cysteines, one of our semi-essential amino acids.  Disulfide bridges are a kind of very strong atomic bond, and they are important for holding proteins together.

References
1) Gorman, M.  Nov. 2009.  "Sulfites in Wine: The Myths, the Facts, and the Truth."  Apartment Therapy: thekitchn.
2) Dec. 1997.  "Health Effects of Sulfur Dioxide."  Canadian Centre for Occupational Health and Safety (CCOHS).
3) Spencer, B. 2010. Sulfur in Wine, Demystified. Into Wine.