Norimaki Synthesizer Taste Display: a tasty sample of science

Imagine a device which could replicate any taste. Millions of dishes, drinks, desserts and snacks and your fingertips or, more accurately, at the tip of your tongue. Introducing the Norimaki Synthesizer, a device which, using electricity, electrolytes and 5 different gels, can produce flavours directly onto your tongue. So how does it all work?

A recent paper by Homei Miyashita from Meiji University, Japan, detailed work on the so-called “Norimaki Synthesizer”, a device which, when held against the tongue, can create tastes through the magic of science. I think this is one of the most interesting pieces of research I’ve come across recently. The paper, titled “Norimaki Synthesizer: Taste Display Using Ion Electrophoresis in Five Gels”, was published this year on the 29th of April. If you want to read the actual paper, you can download it from this website. It’s only 6 pages long and written in pretty straightforward language so while I would recommend reading it, I will be covering the content (and more) in this article, so it’s not essential to understanding this device.

Before diving straight into the science, how about a bit of linguistics? The name “Norimaki” Synthesizer comes from the name of a type of Japanese sushi called Nori rolls (海苔巻き), “nori” meaning the seaweed wrapped around the rice and filling. A food-based name for a food-based device. Hungry yet?

How does it work?

Japanese chemist, Kikunae Ikeda 池田 菊苗

There are current five (widely-accepted) basic taste categories: sweet, bitter, salty, acidic and “umami”. Umami (うま味) is a Japanese word meaning a “pleasant savoury taste”. It comes from the Japanese word うまい meaning delicious, coined by Japanese chemist Kikunae Ikeda. Umami has its own receptors, separate from the other traditional taste receptors, which has made scientists consider umami to be a distinct taste, making five basic tastes overall.

There are currently other taste categories also being proposed, such as Calcium (a bitter and chalky taste), Kokumi (another Japanese word, roughly translating to mouthfullness and meaning a feeling of heartiness), Piquance (the burn from a spicy food) and coolness (that menthol minty fresh taste, among others.

The Norimaki Synthesizer has 5 gels each containing electrolytes which supply certain amounts of each taste. Particular tastes can be created by forming a combination of the different five flavours.

Creating any colour by making
a mixture of red, green and blue

It’s a similar principle to the rgb colours used in LEDs. Every colour can be formed from a certain mix of red, green and blue. For example, to make red, you’d have 100% red and 0% blue and green. To make purple you’d have 100% red and blue but 0% green. To make white you’d have 100% red, green and blue.

The principle is that by combining different amounts of each of the 5 flavours, you can recreate any flavour. The amount of each flavour can be varied by adjusting the amount of voltage flowing to the gel. The more voltage is flowing to the gel, the weaker the taste. So for a sweet taste, you’d want high voltage to the sour, salty, bitter and umami gels, but low voltage to the sweet gel. Just as using red, green and blue flashing LEDs can trick our brain into thinking we’re looking at a beautiful sunset, the Norimaki Synthesizer aims to trick our brain into thinking we’re actually eating something.

By making fries appear saltier, we could reduce the amount of salt people add, a huge health benefit.

In his design, Miyashita was influenced by fellow Japanese scientist Hiromi Nakamura, also from Meiji University. In particular, the concept of “Augumented Gustation” from Nakamura’s 2011 paper titled “Augmented Gustation using Electricity”. Augumented Gustation involved stimulating the tongue using an electric current while eating and drinking to see whether this affected taste. For example, connecting a straw, fork or chopsticks to an electric current to show whether the taste could be altered by an electric current flowing. Nakamura has published several papers since, all focused on using electricity to alter how the tongue perceives taste, including one in which the participants found food saltier when a current was applied. A full list of Nakamura’s work can be found here.

Previous work done by Aoyama et al. in a paper titled “Galvanic Tongue Stimulation Inhibits Five
Basic Tastes Induced by Aqueous Electrolyte Solution” showed that electrolytes could be used to control the strength of the five individual tastes. An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The electrolyte splits into an anion (negatively-charged ion) and a cation (positively-charged ion) when dissolved in solution. The ions spread out through the solution but when a potential is applied across the solution, the anions move to the positive electrode and the cations move to the negative electrode. The movement of the anions and cations constitutes a current.

Why do the cations and the anions move?

The main bit of science behind it is a little thing called “ion electrophoresis” which is the migration of microscopic particles activated by an electric charge. This is the technical name for what is happening when a potential is applied and the cations move to the anode and the anions move to the cathode. Cataphoresis is the electrophoresis of cations and anaphoresis is the electrophoresis of anions.

Electrophoresis occurs because when a potential is applied, an electric field is created between the anode and the cathode. Field lies (the arrows) show the direction a positive test charge would move when placed in the field. In our case, the positive test charge is the cations and we can see from the direction the arrows are pointing that the cations could move from the cathode (positively-charged electrode) to the anode (negatively-charge electrode). Anions would move in the opposite direction.

The difference between the method in Aoyama’s paper and in Miyashita’s is that Miyashita proposed the use of a gel instead of solution. This was to keep the 5 basic tastes separate so the electric current to each electrolyte could be controlled individually, whereas using solutions the 5 electrolytes had to be controlled together.

Aoyama used the following electrolytes for each basic taste:

  • NaCl for salty
  • Glycine for sweet
  • MgCl2 for bitter
  • Citric acid for acidic
  • Glutamic sodium for umami

These are all compounds commonly found in foods with those tastes. For example, you might expect NaCl to be used for salty because NaCl is salt. Citric acid is found in citrus fruits like lemons and limes, glycine is used in many sweeteners (and actually comes from the Greek word “glykys” meaning sweet). The magnesium ions in MgCl2 are bitter, and magnesium chloride solutions are in general fairly bitter. In Japanese MgCl2 is sold as a white powder called nigari (にがり) coming from the Jpanaese word for bitter (にがい). Finally, glutaminc sodium (also called monosodium glutamate or “MSG”) is often used as a flavour enhancer in food.

In fact, Pringles contain MSG and it’s partly why they’re so addictive. Developed by another Japanese scientist Kikunae Ikeda in 1908, MSG exists as a white crystalline solid at room temperature and, while it’s often added to food, also occurs naturally in foods like tomatoes and cheese.

Returning to the synthesizer: Miyashita used the same electrolytes for his gels, creating separate solutions and adding them to heated agar. The agar-electrolyte solutions were then chilled so they hardened to form gels. While there were initial concerns whether the gels would allow ion migration (looked at in more detail below), the gels proved successful. Food colouring was also added to the gels to help differentiate them. Furthermore, after 3 minutes of continued usage while testing the device, none of the gels had lost taste which is evidence for their durability.

The device is wrapped in copper foil- this is the anode. There are platinum wires connected to each of the gels- these are the cathodes. The human body is used to complete the circuit so the device only operates when it is held.

Applying a potential causes cations in the gels to move to the cation (the platinum wires) and away from the tongue- this is why the taste weakens. The current flow to the 5 gels are controlled by 5 variable resistors. The higher the resistance, the less current flow and the less strongly that taste appears to the user. This is how Miyashita was able to change the taste between a sweet “gummy candy” taste and a salty “sushi” taste.

How could the Norimaki synthesizer be used?

Who would’ve thought that in the future we might be able to download a new candy flavour?

If the synthesizer can be reproduced on a wide commercial scale, you’ve effectively produced something that allows you to enjoy the taste of all your favourite snacks, minus the calories. It would certainly revolutionise the diet industry by providing a quick solution to cravings.

It truly does seem like something out of a sci-fi novel. It reminded me a little bit of the chewing gum from Willy Wonka and the Chocolate Factory when I first heard of it. For those of you who haven’t seen the film, Willy Wonka creates a stick of gum which is designed to replicated the flavour of a full three course meal: tomato soup, roast beef and blueberry pie for desert. Of course, in the book/film, it all goes wrong when the girl chewing it gets to the blueberry pie and ends up looking like a blueberry herself…

Looking at an extract from the paper:

Such devices are primarily intended to influence eating and drinking behaviors.

For example, one anticipated application is to make lightly salted foods taste much saltier, which could support a healthier lifestyle by preventing excessive salt intake.

Homei Miyashita. Norimaki Synthesizer: Taste Display Using Ion Electrophoresis in Five Gels, Extended Abstracts of the 2020 CHI Conference on Human Factors in Computing Systems Extended Abstracts (CHI ’20), pp.1-6, 2020.

Here Miyashita references a health benefit that’s currently also being looked at by Japanese scientist Hiromi Nakamura (mentioned previously). This taps into the potential medical uses for technology like this.

During the experiments, Miyashita mentioned wrapping the device in dried seaweed to make it appear more like sushi to enhance the sushi taste to the testers. This raises the question of whether, during commercialisation, the shape of the device might be altered to further trick the mind into thinking what the user is tasting is actually real. The device could be shaped like a soda can for fizzy drinks, or shaped like an ice-cream cone for ice cream flavours.

This brings me to the question of whether the taste alone is what makes a food item recognisable. Would ice-cream taste the same if it was served lukewarm and not it’s distinctive chill? Would many of us recognise it as ice cream, or would we just think of it as super sweet milk? Would we want to sample different soda flavours if there’s no pleasant bubbly taste on the tongue to accompany it.

You might potentially be able to change the temperature of the synthesizer to mimic the temperature of food, making the device cold for ice-creams and hot for hot chocolates, but there are other sensations which contribute to our eating experience, for example thee fizziness on the tongue when drinking soda. How could that be created? And what about the spiciness of a curry? I mentioned earlier that while there are currently five widely-accepted tastes, there are proposals for several more, including spiciness. Would increasing the number of gels, hence the number of tastes available, make the sensation any more realistic? Or would it become like the old saying “too many cooks spoil the broth”.

Unfortunately, no matter how you look at it, the experience would never been the same, no matter how close the flavour is mimicked. Mechanical actions like chewing and swallowing tell our brain important textural information which contribute to our perception of the food. While this might perhaps put a limit on its commercial potential, I’m very excited to see how this technology develops further.

Thanks for reading! You can check out some of my other posts here:

References (link & date accessed)

Watch the official video for the Norimaki synthesizer!

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