Naming the Demons
I
call them the Brimstone Demons because they cause me so much pain. But for
the other 99% of America that is not sensitive, sulfur preservatives are
quite marvelous creatures. When sprayed on fruit and salads, they prevent
enzymatic browning keeping the foods fresh and appetizing. When added to
pickled peppers and red cherries, they maintain the natural, attractive coloring
of the food. When used on shrimp and seafood, they prevent black fungus spotting
and other forms of spoilage. Sulfur oxides perform similar tricks on instant
potatoes, french fries, grapes, raisins, wine, lemon juice, fruit juices,
dried apricots, shredded coconut, dark breads, chocolate mud pies, colas,
cookies, candies of every persuasion, yogurts, syrups, cereals and the list
goes on forever. You may notice I didn’t mention guacamole avocado dip.
It’s just too painful for me; you see, I used to love guacamole before
I learned they were one cause of my headaches.
As preservatives, the FDA allows only a few of the oxides of sulfur to be
used in foods and they go by the following names which may appear on food
labels:
Sodium Sulfite (Na2SO3)
Sodium Bisulfite (NaHSO3)
Sodium Metabisulfite (Na2S2O5)
Sulfur Dioxide Gas (SO2)
The first three are true sulfite salts and potassium may replace sodium in
some formulations. When dissolved in water, they dissociate to free the sulfite
SO3 ion. This combination of one sulfur and three oxygen atoms is a strong
anti-oxidant and explains why sulfites are such good preservatives. Like
other anti-oxidants, they protect food by combining with and neutralizing
free radicals and oxygen. If oxygen is available, sulfite ions readily oxidize
to become sulfate SO4 ions. The sulfate form is quite stable and neither
protects food nor causes pain. Sulfates in food do not cause much trouble
for most people, even those with sulfite conditions. Sulfites should not
be confused with nitrites or nitrates which are commonly used to preserve
meats.
The last chemical on the list above is sulfur dioxide. Strictly speaking,
it is not a sulfite because it lacks the third oxygen atom. However, the
human response to sulfur dioxide mimics the response to sulfites, probably
because it may be oxidized to become a sulfite. As a gas, sulfur dioxide
is one of those nasty air pollutants we all like to avoid. In foods, sulfur
can easily combine with organic molecules taking the place of carbon and
oxygen groups. In fact, there are forms of sealife near volcanic vents on
the ocean floor that survive on sulfur compounds as replacements for the
carbon-based nutrients you and I need. When carbon foods or tree wood is
burned, carbon dioxide (CO2) is produced. When sulfur is burned, sulfur dioxide
(SO2) is produced.
Sulfur dioxide gas is used to prevent discoloration when drying fruits such
as apricots. In the process, SO2 is trapped and bound to the fruit and the
concentration can be quite high. Unfortunately for some of us, sulfur dioxide
is much more than a preservative. Since ancient times, burning sulfur has
been used to temper the fermentation of wine. Most modern wine makers use
the sulfite salts directly, but the result is the same. Sulfur dioxide molecules
bind to the wine and all wine bottles carry the warning "Contains Sulfites".
Sulfur dioxide can also be dissolved in water to have a softening effect
on fibers and other organic structures. This effect is used to advantage
in the corn refining process that produces corn starches and syrups. Corn
refining is no backwoods industry; over the years, corn syrup has replaced
sugar as the number one sweetener in the United States. Since corn refining
starts with sulfur dioxide, all corn starches and syrups wind up with a sulfur
content. And it doesn’t stop there. Sulfur dioxide is an important
ingredient in caramel color, a colorant that is produced in much the same
way as true caramel. Now, I never heard of caramel color before I became
interested in foods. If it’s new to you too, read the list of ingredients
on your next Coke or Pepsi. Diet colas are nearly all water and caramel color.
Regular colas do add a sweetener: high fructose corn syrup, of
course.
How the oxides of sulfur cause problems in humans is not understood. However,
from the above description of their uses in the food industry, it is quite
clear that they interfere with normal biological functions. As a side reaction,
sensitive body tissues swell and cause breathing problems, headaches and
other discomforts. Sometimes it appears that the SO3 ion is the culprit;
sometimes it appears to be SO2 bound tightly, loosely or not at all. Whatever
the form, it would be nice to simplify things. So, I will introduce the concept
of biologically effective sulfur oxide, which I will call SOx. Regardless
of the form of the sulfur, if you know the effective value, you know its
potential for causing headaches and asthma. The SOx value for a food must
be determined experimentally. In my case, I simply eat a food sample, note
my headache response and equate this to a similar headache caused by a calibrated
solution of sodium sulfite. The SOx weight is then defined as the weight
of the SO2 atoms in the calibrated solution of sodium sulfite.
When discussing sulfur preservatives in dried fruits, I mentioned that the
concentration may be quite high. The concentration for dried apricots is
typically 220 PPM. The PPM means "Parts Per Million" and refers to the weight
of the preservative as a part of the total weight of fruit. For instance,
if you divided the fruit into one million parts, 220 of those parts would
be biologically effective sulfur oxide. You can use PPM numbers to calculate
weights. Since food labels like to use grams for weight, we will use grams.
A gram is the weight of ten drops of water.
Grams are conveniently divided into smaller parts called milligrams (mg)
and micrograms (ug). The abbreviation for milligrams is "mg" which makes
common sense. However, the abbreviation for micrograms is less obvious since
"mg" cannot be used. So, the Greek symbol "mu" that sounds like "mew" and
looks like the letter "u" was chosen, presumably by someone that drank too
much Greek wine. As a result, micrograms are abbreviated "ug". It takes one
thousand milligrams (1,000 mg) or one million micrograms (1,000,000 ug) to
make one gram.
You can calculate sulfur oxide weight by multiplying the PPM concentration
by the weight of the food. If the food weight is in grams, the answer will
be in micrograms.
(Food Weight) times (PPM
Concentration) = SOx
In the case of dried apricots with 220 PPM concentration of effective sulfur
oxide, a 4 gram bite would be preserved with 4 x 220 = 880 ug of SOx. That
would give me such a headache, I would have to bang my head against the wall
for hours. That’s all the math you need to know to use food labels to
predict the sulfur oxide content of your dinner. Of course, you have to know
a little bit more about food ingredients, but that’s what the rest of
the book is about.