Have you seen those edible water bottles?

Or the fruity little bubble things you can put on your self-serve frozen yogurt?  I’ve always thought, “Wow, that must be a very advanced and difficult thing to do, but it turns out you can make poppable balls of liquid yourself, with a little help from seaweed. The process is called spherification, and today, we’re going to head over to the lab, which is actually the studio right there, to try it out. [♪ INTRO] .

There are lots of variations online, but the basic chemistry is pretty simple. You’ll need just two solutions. The first is a 0.5% solution of calcium lactate, which is just calcium plus a kind of sugar.

It mixes right into the water.  You’ll also need to mix sodium alginate with whatever liquid you want inside.  That’s the part that comes from the seaweed. Or, more specifically, certain species of brown seaweed, like giant kelp. The alginate is made up of long chains of sugars.

And it’s also water soluble, though sometimes stubbornly. So you might need to give it some time to dissolve, or even use a blender. You may also consider adding some color to it, to help you see it better.  The goal is to get all those sugary chains loosely studded with sodium ions so that they’re floating separate from one another in the liquid.  That way, when you drop the alginate solution into the calcium lactate solution…. chemistry happens!

Almost instantly, a skin starts to form around the outside of the alginate solution, creating a perfectly protected sphere. This happens because the calcium ions displace the sodium ions.  That’s partly because calcium has two positive charges and sodium only has one positive charge.  And those two charges also allow each calcium to interact with multiple sugars at once, including ones in different alginate chains.  So, the calciums form cross-links which bring the chains together and anchor them into place. In fact, for a 2014 article, researchers set up a computer simulation to model what happens to alginate chains with sodium versus calcium.  They found that in the presence of sodium, the chains are loose and floppy.

But with calcium, the whole thing snaps into what they call an ”egg-box” structure.  The alginate chains form the carton, a loose criss-crossed grid pattern, while the calcium ions are like eggs, sitting in the little gaps between the chains and holding the whole thing together.  And since each chain is anchored in many places, if you tried to pull one loose, it would cause other parts to tighten, like a mass of tangled yarn.  So you end up with an interwoven gel. The dense structure is closer to alginate’s natural state in seaweed, which is a big part of what makes them so rubbery and tough.  The trick with spherification is in the method. If you just throw alginate and calcium together, you get a sticky glob of goo.  But if you carefully plop one solution into the other, the reaction happens just at the interface.  So, you get a solid-looking sphere filled with a liquid surprise.

It’s gonna shoot me right in the face, isn’t it? Oh, it did! I knew it!

Now, if you leave the liquid-filled beads in the calcium solution, it’ll continue to diffuse into them, and they’ll eventually become totally gelled.  So if you want to keep a nice liquidy center, you want to fish them out of there, plop them in some plain water to stop the reaction.  Though spherification is a pretty recent trend, it isn’t a new idea. It dates back to a 1946 patent, as a way to make artificial fruits.  Apparently, at that moment, the world wasn’t ready for gelatinous fake cherries. But in the early 2000s, the avant-garde cooking movement took off.  And chefs started having fun with methods like spherification to make super creative and surprising dishes, like an “olive” that releases a gush of salty goodness when you bite it.

Or fruit purees and juices made to look like fried eggs or caviar. It wasn’t long before scientists also started to take note, especially because of the speed of these reactions.   Other compounds like gelatin and agar, can also form edible, cross-linked gels. But they can take hours to set.

But simulations suggest that calcium alginate gels become stable within 150 nanoseconds. That’s one and a half ten-millionths of a second! Which is why it can so perfectly encase your tasty liquid before it has a chance to diffuse away.

Calcium alginate gels are also stable at higher temperatures. That’s unlike gelatin, which, literally, can melt in your mouth. Weirdly enough, the chemicals involved don’t taste like much, so you can’t really tell they’re in there, especially if you add some flavoring.  And you can use just about any liquid!

The main thing you need to know is if it already has a ton of calcium in it, like some fruit juices do.  If it does, you might need to flip the order of the solutions. So, add your calcium-rich juice to an alginate-and-water solution, instead of the other way around.  And, of course, you can further tinker with the chemistry, method, and timing to make coverings that are thinner or thicker, creating everything from a soft gel to something that’s downright gristly. Like for edible water bottles, you might want a really tough wrapper.  I know that may not sound very appetizing.

But you don’t have to eat it.  The key thing here is that it’s technically edible, so it’s also biodegradable! So instead of having a plastic bottle, you’ve got a durable wrapper that breaks down faster than cardboard. Plus, seaweed is a very renewable resource.

Some species can grow more than half a meter per day! And they don’t need land or fresh water. Today, the uses for spherification have grown far beyond fake fruit and avant garde cuisine.  Researchers are using these same basic ingredients to develop all kinds of biodegradable materials, including films, coatings, wrappers, and more.

It’s even used as a biological scaffold for engineering bone tissue. And to manipulate the solubility of things you  can’t normally dissolve in water, like carbon nanotubes.  So be sure to keep an eye on what the fancy chefs are doing.  After all, cooking is chemistry. So they just might be the ones to come up with the next great innovation in material science.  And in the meantime, we get to enjoy their delicious creations.

Thanks for watching this episode of SciShow! And a special thank you to all our patrons on Patreon.  Without our patrons, we wouldn’t be able to make fun episodes like this. Plus, we would miss out on all the silly science memes you post to our patrons-only Discord.  If you’re part of our legion of awesome patrons—THANKS!  And if you’re not, but you think you might want to be, you can learn more about our patron community at Patreon.com/SciShow [♪ OUTRO].