We grow a lot of potatoes in this country: 33 billion pounds to be exact. That’s about 142 pounds of potatoes per person every year. About half are used fresh to make baked potatoes, potato skins, mashed potatoes, canned potatoes, potato soup, potato salad and Mr. Potato Heads. All of these uses of fresh potatoes pose no more of a sulfite danger than any other fresh food. You just have to beware of other ingredients that might be added to such dishes. The other half of our potato crop is processed into french fries, frozen hash-browns, potato flour and dehydrated mashed potatoes. I hate to break the news, but most of those processed potatoes contain sulfites.
Potatoes have a slight temperature problem. If they are stored at temperatures below 45 degrees, the starches can convert to sugars and they can turn brown. If they are frozen, browning can become an issue. I guess that’s why your grandmother told you to keep your potatoes in the cupboard and out of the refrigerator. Any product that contains a frozen potato may have a color problem requiring sulfites. Dehydrated potatoes have similar issues that are solved by sulfite preservatives. Potato flours go one step further and use sulfur dioxide to bleach the final product, giving it a nice white appearance like other flours.
French fries are the kings of processed potatoes and most fries are prepared in a potato factory and frozen before being sent to your local burger stand. The burger people simply dump them into a deep fat fryer for final cooking and serve them to you hot. At the factory, potatoes are cooked under pressure until the skin softens. When the pressure is suddenly released, the skin is jolted loose and it easily peels off in a stream of water jets. The potato skin is used either as cattle feed or to produce methane gas to help run the potato plant. The peeled potatoes are inspected and sent to the cutting machines. The cutting machines are centrifugal pumps that accelerate the potatoes to 50 mph and shoot them into stationary blades. Out pops french fries. The fries are inspected by automated machinery for size, spots and color. Those that pass are blanched in vats of hot water. If necessary, a sugar dip improves the sugar content of the potatoes. Then the fries are dried to controlled water content by blasts of hot air. Finally, they are "par fried" for about a minute and a half in very hot cooking oil. At this point, they are blast frozen and boxed for shipment. Somewhere in this process, sulfites are added because french fries wind up with an effective sulfur oxide concentration of about 13 ppm. For a super-sized bag, this means 2730 micrograms of sulfur dioxide. No thank you, I’ll pass.
Now, the potato industry must have some real muscle. You will remember that the FDA banned sulfite preservatives on salad bars in 1986. In 1990, they proposed to do the same thing for fresh potatoes intended to be cooked and served unpackaged and unlabeled (like french fries). In a protracted court battle, the potato industry challenged the FDA ruling and prevailed on procedural grounds. I’m not exactly sure what all of that means, except this is many years later and sulfites are still all over french fries. My advice to sulfite sensitive people is simple. When it comes to potatoes, unless it is baked whole in its own skin, don’t eat it.
Of course, you also have to watch out for dehydrated potatoes. Dehydrated spuds are used to make instant mashed potatoes. They are easy to recognize when they are in a box on the grocery shelf. But when you’re eating away from home, you have to ask where the mashed potatoes come from before you eat them. Dehydrated potatoes have a cousin, potato flour. You should read ingredient labels and avoid potato flour. Like a fool, I switched from ordinary hamburger buns to Hawaiian buns to avoid high fructose corn syrup. Unfortunately, the Hawaiian buns had a few grams of potato flour that spawned several headaches before I realized what was going on. Potato flour is a sulfited starch that causes trouble for me about 24 hours after eating and lasts for an additional 24 hours. It’s hard to relate your pain to something that you ate 48 hours earlier.
What about potato chips? The bags state "No Preservatives" but can you really believe them? I honestly could find no information on how potato chips are commercially manufactured. I guess the industry protects its secrets. So, I ate a few of Lay’s Classic chips one day, and a few more on following days until I was staring at a full dinner plate of chips. No headache, no problem. Thank you Frito-Lay for not using sulfur preservatives. Of course, after you dine on a full plate of potato chips, it’s a long time before you want another chip.
Potatoes are a good source of starch just like corn. And like corn, they can be refined to produce food starches, maltodextrins and dextrose. In fact, potato starch is more common than corn starch in Europe where American maize has never caught on. In the United States, many factories have been built to refine potatoes over the past century. But potato refining is a somewhat messy business and environmental pressure combined with competition from corn have depressed American potato refining. Maybe depress is too weak a word. There is only one raw potato refining plant left in all of the USA. But don’t fret; the potato waste from french fry and chip factories can be economically refined. So, refined potatoes have begun a comeback. Some french fries are now coated with potato starch to keep them crisp for longer periods.
Since refined potatoes are much less common in North America than refined corn, you won’t run across potato starch on food labels very often. When you do, it will probably be on a soup can. However, food labels do regularly specify just "food starch" or "modified food starch". Such an ingredient could be corn starch, wheat starch, potato starch or any starch. The food manufacturer then has the freedom to use whatever starch is cheapest, most available or works best. Of course, in practice, it will usually be corn starch if the item was produced in America. As far as the oxides of sulfur are concerned, the worst starch is corn starch. So, using the corn starch SOx values for "food starches" is both realistic and conservative. The same comments apply to generic dextroses and maltodextrins.
When we assign a number to the SOx value of an ingredient like "food starch", we are just making a guess. We would like to hope that it is a good guess or even an educated estimate, but we don’t really know for sure. An SOx value is simply an average of the effective sulfur oxide content of a large number of samples. A particular sample might differ from the group average just like the height of any human may differ from the average. So, remember this when you look at the nutrition label on a can of soup and calculate a sulfur content. It’s only a guess. To be more accurate, you would have to contact the manufacturer or run some chemical tests. And even then, what could you say for sure about next month’s can of the same soup?