We’ve all been there. You open a packet of crisps to find that only a tiny fraction of the bag contains the starchy goodness you paid for. Have crisp manufacturers been continually deceiving us, or is there a good reason for the apparent abundance of air in crisp packets?
It turns out that crisp packets don’t actually contain the same air that we breathe: they contain pure nitrogen gas. Atmospheric air contains around 78% nitrogen and 21% oxygen, with the remaining 1% being comprised of carbon dioxide, water vapour and some other rare gases. This means that the gas in crisp packets is basically air without oxygen, and this small detail is very important in maintaining the quality of crisps.
Crisps, like many foods, go stale when exposed to oxygen. But by filling crisp packets with nitrogen, manufacturers delay the exposure of the crisps to oxygen, thereby delaying the oxidation process and allowing the crisps to maintain their consistency for a longer period of time. One study by CDA verified this by comparing the shelf life of a variety of crisp brands with the proportion of nitrogen they contain. The study found that a brand called Pop Chips, of which a single bag contains 72% nitrogen by volume, also had the longest shelf life, which was 55 days. They concluded that filling a bag of crisps with more nitrogen allows the crisps to enjoy a longer shelf life.
Preventing crisps from going stale is important in maintaining their taste. A study carried out by the University Of Delaware involved training a panel of tasters to “evaluate the sensory quality of potato chips”. While this study may not have done much in the realm of improving the reputation of the University Of Delaware, which is now often the butt of jokes related to useless research, the study did yield some interesting results. They conclude that crisps exposed to oxygen undergo a process called lipid oxidation. They found that there is a small change to the extent of lipid oxidation as a result of filling bags with nitrogen, and their panel of trained tasters were actually able to taste the difference between bags filled with different levels of nitrogen and oxygen.
Some manufacturers claim that they fill crisp packets with nitrogen in order to protect the crisps during transport. A statement from Walkers reads: “There is a very good reason for the packets not being filled right to the top. Crisps are very fragile and can get crushed very easily. To try and prevent this from happening, we put [nitrogen] in the packs before they are sealed to act as a cushion for the product during transit.”
It turns out that adding nitrogen does not actually provide any added protection to the crisps. An artist called Henry Hargreaves found that the exact opposite is true: bags filled with more nitrogen were more likely to have broken crisps. He suggests using vacuum packed bags instead, which would better protect the crisps and allow for more efficient packaging and transport, thus making the bags more environmentally friendly. Vacuum packed bags would however be more expensive than the current packaging methods, so I can’t see manufacturers adopting this ambitious artist’s suggestions any time soon.
Crisp manufacturers will continue to use nitrogen to fill their bags, as long as it offers a cheap way to keep crisps from going stale. It is important to note that it is not the presence of nitrogen, but the absence of oxygen which preserves the crisps. Any non-toxic gas could do the job, but nitrogen is both cheap and abundant, factors which make it extremely attractive to manufacturers.
Next time you open a packet of crisps and find only a handful of crisps at the bottom, remember that there is method behind the madness.