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Every once in a while — less often than a few years ago — you’ll open a bag of potato chips and see one which isn’t like the others. It’s green-ish, especially around the edges. It is safe to eat, though it is poisonous. Confused? Read on!

Potatoes grow underground and are shielded from sunlight — usually. Sometimes, parts emerge above ground, and those sections turn green as chlorophyll develops. And for this to happen, the light need not be natural light. Most green potatoes don’t make it to the stores — be it in the produce section or in crinkly foil bags — for a variety of reasons, but really, who wants to eat a green potato?

That said, on occasion, a green-tinted potato may find its way into a potato chip factory and, eventually, a slice thereof may sneak into a bag of chips. (It’s less and less likely though, due to advances in technology. Here’s a video showing how potato chips are made in a large factory setting; if you fast-forward to about 2:50, you’ll hear about the cameras used to identify and reject flawed chips.)

Chlorophyll is non-toxic and harmless, but, as mental_floss points out,

in the process of a potato going green … conditions are right for it to synthesize more of a glycoalkaloid (alkaloid + sugar) poison called solanine, which potato plants produce in their leaves, stems, sprouts and flesh as a defense against insects and other predators.

Solanine is not just bad for insects, in large enough amounts, it is really bad for you — it can cause “vomiting, diarrhea, headaches, and even paralysis of the central nervous system,” per Snopes. In the most extreme case, it can even cause death.

But don’t worry too much. One would have to eat about 10-20 or so green potatoes in a day to fall ill. A medium-sized potato yields about 36 chips, per the video linked to above; it’s safe to say that if you ate 360-720 potato chips in a day, you’re going to get somewhat sick, even if the chips aren’t of the green variety. And, of course, unless you purposefully made them yourself, you’re not going to encounter that many green potato chips perhaps even in your lifetime, let alone in a single day. So if you come across an occasional green chip, odds are you’re fine eating it.

On the other hand, don’t eat the green sprouts or leaves from the potatoes themselves, as they have very high levels of solanine. As the Straight Dope recounted – a story which is likely apocryphal, but regardless, demonstrative — “during World War II some refugees broke into an abandoned house and found a quantity of old sprouted potatoes in the basement. The potatoes themselves were too dried out to eat, so the refugees made a stew out of the sprouts — and got incredibly sick as a result.”

So, for perhaps the only time ever, this is one case where a vegetable’s fried yellow chips are better for you than its green leaves.

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Bonus Facts:

Ever wonder why, when you open a bag of chips, there’s all that empty space where extra chips could be? They don’t do that to rob you of snack food. Rather, the extra space is there to make your snacks taste better. As About.com explains, the space isn’t air like the air we breathe — there’s no oxygen in it. Chips exposed to oxygen will start to spoil, so instead, food packagers inject nitrogen into the bag, allowing the chips to bounce around freely without breaking and yet, not causing spoilage.

In case you’re curious, dark brown potato chips are not caused by overcooking the chip, but rather are caused by the potatoes being stored at cold temperatures for an extended amount of time (too long in this case). Normally the potatoes have a certain amount of sugar present that when cooked, with the aid of some amino acids, gives the chips the somewhat standard yellow tinge. However, when the potatoes are stored at cold temperatures too long, more sugar is built up, resulting in the chip turning dark brown when cooked, sometimes so much so that it almost appears burnt.