I understand that we fill potato chips bag with nitrogen to prevent oxidation. But why do we use nitrogen, instead of neon or hydrogen or something else?
My first guess is that nitrogen is lighter than neon/argon but what about hydrogen or helium?
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48$\begingroup$ Because nitrogen is cheap. $\endgroup$– Nilay GhoshJun 19, 2020 at 3:12
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33$\begingroup$ And doesn't explode. $\endgroup$– henningJun 19, 2020 at 13:06
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15$\begingroup$ Hydrogen? So you want chips bag floating around like balloons and have to be hold down? $\endgroup$– stackoverblownJun 20, 2020 at 14:52
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11$\begingroup$ Nothing is better than chips freshly baked in hydrogen flame. $\endgroup$– PoutnikJun 21, 2020 at 14:31
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$\begingroup$ From personal experience (traveling to a number of different customers in behalf of Lako Tool to install heated bag crimpers ("sealing jaws") on vertical form, fill, and seal wrapping machines), I have never seen any gas nozzles that would fill the bags. In fact, that could inflate the bags and therefore interfere with the sealing process. $\endgroup$– Mike WatersJul 29, 2020 at 16:06
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4 Answers
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As Nilay Ghosh said, nitrogen is cheap. Very cheap. Neon is expensive. Argon is cheaper than neon, but considerably more expensive than nitrogen. Helium is also expensive and needs to be used wisely, for important things, e.g., cryogenics. And hydrogen! I can just see the ads: “Buy our chips: they are lighter than air! But avoid open flames and sparks unless you want to be Hindenburged to a crisp (no pun intended)”
Another fill gas to avoid is sulfur hexafluoride. A tennis ball manufacturer once decided to fill tennis balls with sulfur hexafluoride, assuming this would prevent the balls from going flat as a consequence of the high molar mass of sulfur hexafluoride. But the tennis balls exploded on the shelves because air diffused in.
Thankfully, no one has ever tried using nitrous oxide as the fill gas in potato chip bags!
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$\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$– user7951Jun 19, 2020 at 19:27
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$\begingroup$ Also, SF6 is the most potent known greenhouse gas, with a global warming potential of 23900. $\endgroup$ Jun 20, 2020 at 9:51
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13$\begingroup$ Funny as it may seem, if the bags were filled with nitrous oxide I'm guessing a lot of folks would buy them for the gas. $\endgroup$ Jun 21, 2020 at 0:56
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13$\begingroup$ Nitrous oxide would be a bit of a laugh. $\endgroup$ Jun 21, 2020 at 16:20
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4$\begingroup$ Nitrous oxide is an oxidiser and would cause the oils to go rancid faster. $\endgroup$– KalleMPJun 21, 2020 at 17:01
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Not mentioned yet: nitrogen is entirely non-toxic, environmentally friendly, does not contribute to global warming or ozone depletion.
In very good approximation, nitrogen is just air with the oxygen removed that would oxidize the contents. The usual production process consists of liquefying air, distilling it, and then selling the gases separately. This makes food-quality nitrogen very cheap. It's not a huge problem if there's 1% oxygen left in the bag.
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12$\begingroup$ Not sure about the case of potato chips, but there is often used mixture 80% nitrogen + 20% carbon dioxide, probably to actively suppress eventual growth of anaerobic microflora. That applies probably more on animal products like meat. $\endgroup$– PoutnikJun 19, 2020 at 18:49
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4$\begingroup$ I'm recalling when I was working in research for the Air Force, we would get liquid nitrogen for our equipment that was a by-product of the production of liquid oxygen for aircraft. $\endgroup$ Jun 21, 2020 at 0:58
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5$\begingroup$ oxygen and nitrogen separation by fractional liquidation is done in large scale in iron/steel processing industry, as using pure oxygen is reportedly cheaper than air, reaching high temperatures easier and avoiding useless warming up of nitrogen. $\endgroup$– PoutnikJun 21, 2020 at 14:38
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$\begingroup$ @Poutnik: The process also yields argon, which is a valuable gas for welders. At welding temperatures, nitrogen is no longer inert, but argon is a noble gas. Nitrogen is really what remains when the valuable stuff is sold. $\endgroup$– MSaltersJun 22, 2020 at 23:39
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Substances that are gaseous down to, say, -10 are finite (and not very large) number.
Of these, we want:
Safe against ignition (so no hydrogen or gaseous hydrocarbons)
Not poisonous (phosphine, arsine, carbon monoxide - out!)
Not corrosive (chlorine, fluorine - sorry)
Without unpleasant smell (hydrogen sulfide is no-go)
Not related to processes of food degradation (oxygen)
Low diffusion in everything, in order to stay into the package (helium, go home - but sometimes used in cans)
Environmentally friendly (CFCs and friends - great if it wasn't for ozone layer)
Cheap (krypton, xenon - stay away from our mass products)
A lot of them fail more than one of the above.
And those that pass, have to be approved by local food quality regulator.
What we have left:
Nitrogen - numero uno for inert packaging. Cheap as hell, inert for all practical purposes.
Carbon dioxide - a bit more expensive, easier logistics (lower pressure tanks), less suffocating potential (heavier than air and has some smell), alters the taste a bit (but not always bad - see soda drinks).
Argon - adds a touch of luxury, otherwise just like nitrogen. Sometimes just not separated from nitrogen. I have seen it used in an occasion when nitrogen is off.
Air - cheaper than nitrogen and still contains ~80% nitrogen. Sometimes mixed with nitrogen in order to get the oxygen down to acceptable level.
p.s. other gases can be food-grade as well, including, but not limited, to hydrogen, nitric oxide, sulfur dioxide, oxygen, ammonia. They are used for other purposes in the food industry, but not for packaging.
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2$\begingroup$ @EdV yes, but CO is related to processing and not to packaging. $\endgroup$– fraxinusJun 19, 2020 at 19:07
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The reason to employ nitrogen in place of air, in addition to a cost advantage, is the fact that air contains oxygen, possibly water vapor, dust particles (containing trace amounts of transition metals) and even microbes (bacteria, mold spores,...) as well.
Upon warming with time, I would not expect that such a mix is a good inert medium to store/preserve food.
While using hydrogen may provide some marketing hype, my experience is that the gas is very adept at escaping and any mixing with air followed by accidental ignition may result in burns. So just adding pure N2 from liquid nitrogen is probably a better idea.
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$\begingroup$ There is a cost advantage for using nitrogen over air? $\endgroup$– hkBstJun 21, 2020 at 12:37
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$\begingroup$ @hkBst depends. Are "customer returns" treated as an externality? $\endgroup$ Jun 21, 2020 at 14:52
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1$\begingroup$ @hkBst Nitrogen will cost more than air unless it happens to be in excess as a by-product in close proximity with transport cheaper than compressing/pumping air. However the reason to use Nitrogen is to avoid the oxygen in the air. $\endgroup$– KalleMPJun 21, 2020 at 17:06