Have you ever wondered how many calories are in a laptop?

Probably not. Because nothing about your  personal computer screams "I’m edible!", let alone “I’m delicious!” But in one odd corner of science, researchers are constructing computer parts from edible ingredients.

And while we might never pull all those together to build a CPU that you can have for lunch, there's a good reason these  experiments are on the menu. [intro jingle] On our journey to build an edible computer, let’s start with the power supply. Since it’s generally considered a bad idea to lick a power outlet, our edible computer will run on battery power. But before we introduce the version you can eat, let’s review the important parts  inside any kind of battery.

Basically, you have two halves  that make up the “terminals” you connect up to a circuit. There’s the anode, which accumulates lots of  negatively-charged electrons, and the cathode, which is missing a bunch of electrons and therefore positive in charge. They’re separated by a substance called  an electrolyte that, as the name suggests,   lets electric charge flow through it.

But not all of the electric charge. See, inside a circuit, the anode loses electrons in a chemical process called oxidation. The electrons flow through the circuit, delivering power to whatever you’ve got hooked up, before arriving at the cathode.

Meanwhile, the anode also releases  positively charged molecules that were made by all those electrons  hitting the proverbial road. And those molecules flow through  the electrolyte toward the cathode, giving it its net positive charge. Finally, as electrons complete  their loop of the circuit, they join back up with the positive charges at the cathode by way of a  process called reduction.

Combined with the electrolyte stopping electrons from taking a shortcut straight  from the anode to the cathode, the oxidation and reduction reactions at the two terminals drive  electrical power through the circuit. These terminals are also a reason why eating batteries is usually a terrible idea. Most consumer electronics use  lithium-ion batteries whose cathodes, and the bits surrounding them, contain  toxic metals like cobalt and nickel.

But remarkably, you can make anodes and cathodes  from edible materials too. The key insight is that oxidation and reduction reactions also happen inside your body, including when your body breaks down the  nutrients it gets from food. So for a paper published in 2023, some Italian researchers set out to build a completely edible battery.

The anode was made from vitamin B2, and the cathode was made of quercetin, which is an antioxidant found  in fruits and vegetables. They also used a water-based electrolyte with seaweed to stop the  electrons going the wrong way, and added some activated charcoal ... which yes is not a food  but you can safely eat it… to increase how well the charge would flow. Wrap it all up in beeswax, add tiny bits of safe-to-eat gold to serve as a couple of electrical contacts, and voila: you’ve got an edible battery.

It wasn’t exactly gourmet cuisine, but the setup did function as a real battery for twelve whole minutes. And while it was only able to produce 48 micro-Amperes of current, that’s enough to power a low-power LED bulb. So with time to finesse this proof-of-concept, we might see edible batteries getting put into actual devices.

Maybe not the phone you use to order food directly to your door, but they could power ingestible medical devices. Or if you scale them up a bit more,  you could use them in kids’ toys. Because not only do we have to worry about curious tiny humans sticking things in power  outlets that they shouldn’t, we also have to worry about them sticking things in their own mouths.

But let’s move from edible batteries to the next component of our edible computer: The circuitry. Lucky for us, there’s been progress on that front, too. To avoid a tangle of wires, computer chips feature circuits that have been printed directly onto them.

The ink is electrically conductive, and the board is insulated  so the current doesn’t leak. But just like batteries, the materials that make up most circuit boards will wreak havoc inside your body… even if you ignore the fact that they’re so hard and  rigid your digestive tract would just absolutely hate you. But it turns out there’s a  material we can use to make soft, flexible and waterproof circuit boards: Kombucha.

Love it or hate it, Kombucha tea is brewed using a SCOBY, or “symbiotic culture of bacteria and yeast”, stuck together in a mat of cellulose. And, as it happens, SCOBYs can double as flexible, tough sheeting for circuit boards. In one 2023 study, researchers printed functional  electrical circuits onto dried out SCOBY.

Unfortunately, scientists don’t exactly know if the electrically conducting  “ink” this team used is safe to use inside the human body. But those Kombucha circuits were safe enough to put on skin. And the team hopes that, in the future, you might weave them into fabrics to  create new “wearable” biomedical sensors.

As for a truly edible,  electrically conductive ink, a different team of researchers mixed together some beeswax and vegetable oil, then added tiny particles of activated carbon to make a paste that can carry electrical charge. They applied it to the skin of an apple, and successfully observed an electrical current flowing through a completed circuit and powering… you guessed it…an LED. In other words, it seems like we have edible versions of both the stuff we print circuits with, and the stuff we print circuits onto.

But for us to create an edible computer,  there’s still one hurdle to clear. Because in order for them to compute stuff, computers need very particular  types of electrical circuits called logic gates. Logic gates take input signals of ones and zeros, and use some kind of “logic” to produce an output signal… of either a one or zero.

For instance, there’s the NOT gate, which takes a single input of zero or one, and returns you whatever that input is not. In other words, it turns a zero into a one, or a one into a zero. It’s weaving gates like this together into bigger and bigger layers  of sophisticated operations that gets you the world of modern computing.

Whether you’re talking about  a solar-powered calculator or your laptop that begs for mercy when you try to play Baldur’s Gate 3. Now, in theory, we could power logic gates with that edible battery we talked about. But a tiny current isn’t up to the task of powering the millions of logic  gates inside a modern computer.

And for safety reasons, you probably don’t want large electrical currents inside you, either. Which is why, in one 2023 study, Swiss researchers created logic gates powered not by electricity, but by an edible fluid. Basically, the gates were valves made of cellulose and zein, which is a plant-based  protein extracted from corn.

And the valves were meant to either restrict or release a flow of extra virgin olive oil. But that’s not all. In order to control the valve, the team used an external source  of pressure: more olive oil.

So when there’s pressure from the “input” oil, the valve shuts and stops the flow of oil going through it. And when the input is turned off, the valve can open up and let the internal source of oil flow freely. In other words, the researchers created a “NOT” gate  that inverts a fluid-based signal.

But they pointed out in their paper that this could be scaled up to create even more complicated, but still completely edible, logic gates. And if that’s the case, you could hypothetically replicate the exact same logic performed in a non-edible computer. However, we should provide  a quick reality check here.

This is just a single logic gate, and simply adding two numbers together requires dozens of logic gates, at minimum. But even a single logic gate has  some surprisingly tasty applications. For instance, in a study from 2022, researchers created an AND gate out of a blend of agar jelly and fruit gummy, which could be filled with different  colored, and flavored, fluids.

An AND gate outputs a signal of one if and only if all of the  input signals are also one. Otherwise, it outputs zero. So in this edible version, a little heart shaped pattern would appear if and only if both ends of the logic gate were squirted with liquid.

That experiment is unlikely to spawn a full on jelly computer. But it was, according to the study participants, delicious. So we might have to wait more than a while for an even slightly edible computer to come on the market.

But if one ever does, you can be sure of one thing: Someone’s gonna get it to run Doom. Thanks for watching this episode of SciShow. If you want to learn about even more completely unexpected ingredients that scientists have used to build a battery, you should check out the episode we did for our podcast, SciShow Tangents.

Not only do our hosts Ceri, Hank, and Sam hit upon one of the edible  batteries referenced in this video, they also cover how scientists have turned animals into batteries, too! Which animals exactly? I’m not going to spoil it for you.

You gotta go listen for yourself. So just scroll a little bit down and click on the link below. [ OUTRO MUSIC]