How do you know if food is past its best?

How do you know if food is past its best?
02 July 2019

Interview with 

Firat Guder, Imperial College London


A food market with a wide array of different vegetables.


A new, ultra-cheap food sensor can tell instantly whether your chicken thighs are still good to eat. It’s called the ‘paper-based electrical gas sensor’, and it might just save supermarkets wasting some of the millions of tonnes of food they throw away every year. Plus - it can even connect directly to a smartphone. Firat  Guder from Imperial College London is the device’s inventor, and he told Phil Sansom how he came up with the idea...

Firat - Paper carries a substantial amount of water that would allow us to do wet chemistry without ever adding a single drop of water to paper. So you need, essentially, liquids to do chemistry often times, and this liquid is absorbed from the moisture in the air. It turns out that the environmental gases can actually interact with this layer of water that's absorbed in the paper, and by measuring just the electrical properties of this layer of water we can determine if a certain gas is in the environment.

Phil - How does the gas affect the electrical properties?

Firat - For example, if there is ammonia gas in the environment it can actually come and then dissolve in this layer of water into ions. With the increased concentration of ions there is also an increase in conductivity of this layer of water. So by just measuring the ionic conductivity we can essentially measure the concentration of, let's say in this case, ammonia.

Phil - Oh. So like if you measure how well the piece of paper conducts electricity, that goes up if there's ammonia in the air?

Firat - Precisely, yes. The sensor itself is more sensitive to water-soluble gases, and ammonia is a highly water-soluble gas so it's really, really sensitive to ammonia, but it is also sensitive to other water-soluble gases such as trimethylamine and even carbon dioxide.

Phil - And it's basically just paper right, so that's why it's dead cheap?

Firat - They cost about two cents. And, through high-volume manufacturing, we estimate that, probably, we can decrease the price about a thousand times.

Phil - What are you going to do with it?

Firat - We have a very inexpensive sensor that performs really well, so it was just, to me, that obvious that this would be a really useful technology in sensing spoilage in freshness of meat products. Because meat is protein rich, when the proteins decompose they release a lot of ammonia and trimethylamine and so on - nitrogenous compounds.

Phil - So are you anticipating that you can use this as a sensor inside the packaging of meat to tell whether it's actually gone off or not?

Firat - Yeah, precisely. I started talking to various managers at grocery stores just to see what they think about this because clearly the literature says that food waste is a big problem. Well, first of all, this was a really difficult thing to do because it turns out that most grocery stores were not really interested in sharing their stats with an outsider. They don't want to tell people how much food they throw away, so I had to actually build personal relationships with some of these managers to, I guess, gain their trust.

One of the things that I noticed is that the meat products, which are considered to be high value, they already contain various electronic components that are embedded inside the packaging itself. And the most known examples of this is near field communication tags, such as the ones that are used in Oyster cards and so on. And this allows retailers to really monitor their inventory and because our sensor is electrical, it turns out that we can integrate our electrical sensors onto these disposable near field communication tags that are already in place with meat packaging. By making components or making smart tags that would allow them to also monitor the freshness of foods, they think that they would be able to save a lot more money and throw away a lot less food.


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