Introduction: Growing Rock Candy in Only a Few Hours!!

Today I am going to demonstrate a technique I had developed to grow rock candy crystals in just a matter of a few hours, instead of the conventional several weeks.

This technique is quite simple, but we will be working with hot sugar liquid here, so this is only to be attempted by someone responsible, and qualified to do it safely. That means if your are just a kid, don't try this without Parent or guardian supervision.

Now that is out of the way, we need to go over what we need. First thing we are going to need is a pot to cook the sugar solution in. We also are going to need a candy thermometer, in order to determine the stage at which the sugar solution is cooking at. If we don't have one of these it can be almost impossible to get this right.

Were also going to want a measuring cup... Sugar of course, water, and a container to grow the crystals in. I am using a heat resistant plastic container, but I would suggest using something like a canning jar, as they are able to handle some high heat without risk of breaking.

We also need something to grow the crystals on, I am using a piece of string, and of course if you plan on eating your crystals you want to make sure it is clean and safe to eat off of. And equally important something to suspend the string off of, I am going to use that pen.

Other than that, so long as you have a controllable heat source and a spoon, you should be good to go.

Step 1: Add the Ingredients

Picture of Add the Ingredients

-Take your measuring cup, and measure out roughly 4 cups of sugar, and add it to the pot. As you can see my sugar has clumped up, and would be annoying to try and use for normal baking. So this is a perfect way to use it up.

-Secondly, you'll want to add in one cup of water.

That's as far as ingredients goes for right now.

Step 2: Cook the Solution

Picture of Cook the Solution

After that you'll want to turn on your
thermal range, what ever it may be, to around medium-high. From here on out we want to watch the sugar water solution very closely, and mix it frequently as to assure it can not burn or caramelize.

Also make sure you keep a good eye on your candy thermometer, we need this to get too 230F (110C) or the Syrup stage for sugar. If we bake it to short, it may take a really long time for your crystals to form. We bake it to long, and your crystals may form so fast you don't have the chance to get your seed strand in it before it turns to a solid block of sugar. Also try to keep your thermometer from touching the bottom of your pot for the most accurate reading.

Step 3: Prepare Your String

Picture of Prepare Your String

So while that's cooking, let's see if we can't prepare what we are actually going to grow the crystals on.

The key here is to make sure that we have the string placed where it close to the bottom, but not actually touching it. About and Inch from it should be good. Once we get that marked, next we'll need to tie the string to the Pen, or whatever you may be using for the bridge. If you have excess string you can either cut if off, or like I did wrap it around several times before tying it.

And for now we can set that back off to the side, and continue cooking this.

Step 4: Continue Cooking, and an Explamation of What's Occuring.

Picture of Continue Cooking, and an Explamation of What's Occuring.

Now what we are doing is removing as much of the water out of the solution as possible, creating a super saturated solution. As time passes, and the solution cools the sugar is forced out of it and crystallizes. It is essentially the same thing that happens when you let the sugar crystals grow over the course of weeks, except that instead is using evaporation.

Now the main difference is, that even though when we cook this solution and the concentration of Sugar to Water is way higher than the evaporated solution, the cooked solution doesn't instantly force out the sugar from it and have it crystallize... Why is that... Is it just from the heat..?

Well no, or not solely at least. It is true that the heat will allow for the Sugar-Water solution to hold a higher concentration of sugar, but that isn't the only reason it stays liquid. What I mean is this solution will take around 16 hours to harden fully, yet it cools off completely in around 3 depending on the container it is put in. So even though it is cool, the sugar isn't forced out and to crystallized right away.

Well this is because of a Phenomenon called super-cooling, or at least in part. Cool, what does that have to do with a hot solution..? Well let's first look at what exactly super cooling is, it is a phenomenon when a Liquid or gas does not turn solid even after being cooled past it's freezing point, now a freezing point is not necessarily cold as many people like to believe, a freezing point is just a Temperature in which something turns solid, that does not mean it's cold in the least bit, well at least not by our perspective.

For an example, the Freezing point of Iron about is 2,799 Degrees F, touch that temperature with your bare skin and I can assure that frost bite will be your last concern. So with this mind let's understand, that just because the sugar is Hot or warm does not mean it can't be Super-Cooled, once again it is all perspective.

So the reason the solution takes so long to form crystals and doesn't turn into a solid block while it's cooking has to do with a few factors.

One, even tough we have cooked out enough water that crystals can form and should start to form, they don't do to the super-cooling phenomenon in which a crystals can't form without a nucleolus to grow on.

And two, Sucrose otherwise know as sugar, takes a certain period of time to actually form crystals depending on the crystals structure.

So the stuff will stay liquid for a time, until it finds something to nucleoli off of. This could be a Speck of dust, a scratch in the container or any number of other imperfections. The rougher they are the better. But the smaller the imperfection, the longer it will take the crystal to grow, as there is reduced surface area.

So how we stimulate the crystals to grow is using something called seed crystals, or in our case a strand of seed crystals. This will provide the nuclei point in our super cooled solution to allow the crystals to start growing. And by doing this, help limit it from growing on the walls of the container instead of the string.

If you want to see a more dramatic demonstration of a super cooled solution look up a Sodium Acetate otherwise know as Hot ice, demonstration.

So now that the long winded sciencey explanation is over, let's continue to bake the sugar solution.

If the sugar starts to bubble up like this, don't panic it is alright, just make sure that you dial down the heat a bit as to insure it doesn't bubble over the sides of your pan and make a big mess.

A few minutes pass, and we are about to reach the syrup stage, my pot is starting to bubble up again, and as you can see they are a lot thicker now. Notice though now when they break my solution has become clear, that means the sugar has dissolved.

looking at my thermometer we have reached the syrup stage, we can turn down the heat now, and let it sit until it cools to around 220 F before we add any flavorings, coloring, or transfer it to the growth container.

Step 5: Prepare Your Seed Crystal Strand

Picture of Prepare Your Seed Crystal Strand

While that is cooling, we can prepare the seed crystal strand. This is simple, I'll just take the string I had prepared prior, and dip it in the sugar syrup. You might have to use a spoon or something to really get it to coat. After that, take the string and coat it using some granulated sugar, this sugar will act as our nucleation point.

Step 6: Add Flavorings, Colorings and Transfer It to Growth Container

Picture of Add Flavorings, Colorings and Transfer It to Growth Container

Once cool to about 220F, you can now add in some flavorings and colors
if you want. I am simply going to add in some vanilla flavoring for mine.

Once that has been done, if you are
going to do it... You can transfer the syrup to your growth container. This is the part you need to be most careful during, you don't want to spill any or make a mess but at the same time you don't want to get this stuff on your skin, It's not called confectioners Napalm for nothing after all.

When you successfully do this, you can now add your seed strand, it might try to float, in which, you should be able to rise it up a down a few times to straiten it out. once that that has been completed, now possibly the hardest part. Waiting for your sweet treat to grow.

I'm going to leave this for four hours, but you can wait more or less depending on how big or small, you want your treats to be. Make sure you don't leave it sitting for too long though, as if you do you might come back to a block of sugar.

Step 7: Let It Grow... Let It Grow! the Wait Never Bothered Me Anyway ;)

Please drop me a Comment, a Favorite or a Vote if you got the reference in this steps tittle :)

Anyways If you want to see the time lapse just of it growing, start the above video and skip it ahead to 9:07s. The footage there was taken over the course of four hours, but even after 1 hour the crystal has quite a bit too it.

The above photo is the Crystal at 4 hours of growth, it is now ready, in my opinion to be removed.

Step 8: Remove, Dry and Enjoy Your Treat!!

Picture of Remove, Dry and Enjoy Your Treat!!

So now that it's been given sufficient time to grow, I am just going too pull it out of the solution. If the crystal does not want to come out easily, you might have to get a spoon in there, by the side and try to wiggle it a little and free the crystal strand.

Luckily mine can out fairly easily. As you can see, it is thick with syrup though. All we have to do is hang it up in another container, and let the excess syrup drip off of it. When it is done it should look something like this.

Now you can see it here next to a quarter for size comparison, not bad at all for four hours growth. Well thank you guys very much for watching, and if you enjoyed the video Please remember to comment, rate and subscribe!!

On one last note, don't leave the excess syrup around to harden otherwise you might have a sugar brick left in your container. It can be cleaned out with hot water, but is a major hassle, and best to avoid.

Thanks again, and bye!!

"Hey everyone thanks for reading this Instructable, I just want to let you all know all your Support means a lot to me, and makes it worthwhile! This video took 1 day to record, two days to edit. And to bring it here to you wonderful people on Instructables took me another 3 hours to type up, and compose. So all of this is no easy task, and I can only do it because of your support!! Thank so much everyone!!"


bravoechonovember1 (author)2015-06-02

looks tasty!

will it keep growing after 4 hrs?

yes it will

4043077 (author)2017-11-06


4043077 made it! (author)2017-11-06

i loved it it is awsome i made 3 crystals in 2 hours but one was to big and it filled the jar qnd i cant take the crystal out lol

jbc2 (author)2015-07-17

Fat finger post...

Anyway, run a designed experiment...ANOVA, figure out significant factors, build the model equation, then use some calc to fun! Also, this makes me feel I'll just daydream about doing this :)

jbc2 (author)2015-07-17

It would be interesting to run an experiment on making rock candy. May be a good project for a cold winter day, armed with likely factors / variables

TC78 (author)2015-02-23

Awesome, definitely going to try this. Thanks :)

TrollFaceTheMan (author)TC782015-03-14

Thanks for commenting, and good luck!!

TrollFaceTheMan (author)TC782015-02-23

Np, and thank you for commenting!!

Cat00x (author)2015-03-03

When i was a kid I tried to make rock candy but it never stuck to the string. I guess I never got the sugar hot enough! Thanks for this very detailed and interesting instructable. At this point in life I think I'm more likely to just put a spoonful of sugar in my mouth than go through the hassle. But I think this is great for kids to see.

TrollFaceTheMan (author)Cat00x2015-03-14

The magic has gone out of it eh..? XD

guds777 (author)2015-02-26

But if you use something like a Maple syrup or something similar, is it not possible to add some color to it...

No, you can't add flavoring or color to it. Growing up my family made syrup every spring, when you cook sap down it creates maple syrup. Cooking it farther is the process that creates maple sugar candy and it's color is naturally brown and it's already flavored.

But what if he wanted something like Maple Cherry..? He would have to add flavoring in it...

If using pure maple syrup the flavor gets stronger as it cooks down, in that process you're not cooking it until it becomes smooth. In fact the syrup starts turning to sugar. Adding a flavor to that wouldn't taste very good. This coming from 40 years of making candy. If you want a maple flavor use the recipe in the tutorial and add some maple flavor oil. Loran makes wonderful flavor oils and a huge variety. A small 1 dram bottle is enough for 1 batch. To mix flavors make a double batch. There are so many flavors though you might not want to mix any.

No, I do get that Maple Syrup is naturally Maple flavored, but what I'm getting at is. Adding flavor to it is doable if you really want to, it's not like going to break it or something XD.

Like strawberry maple, or blueberry maple, or maple and tea some people like.

TrollFaceTheMan (author)guds7772015-02-26

I'm not quite sure what you mean... Are you asking a question..?

filiatraultcampbell (author)2015-03-03

Would it work with the same process I use for hard tack? Only instead of pouring it into a cookie sheet I could finish it with string? Right now I use 3 cups sugar, 1 cup light kayo and 1 1/2 Cups water. Cooked until 310 degrees remove from heat add my flavor oils and color.

Is it supposed to end up like a taffy..?

My8thLife (author)2015-02-26

I read your recipe and am hoping to try it. However, I am confused about one part. You say to bring the syrup to 230°F. Two steps later you say to continue cooking. Do you mean to continue cooking at 230°F, or is there another temperature involved that I am missing.

Max temp should only reach 230F

Seagrey (author)2015-02-26

I think the slow articulate language makes this useful for an even wider viewing demographic. Well done! I’m middle aged and I want to try this : ) Voted!

TrollFaceTheMan (author)Seagrey2015-02-26

Well thank you very mich sir :D

Seagrey (author)TrollFaceTheMan2015-02-26

And/or Madam : )

TrollFaceTheMan (author)Seagrey2015-02-26

Sorry I use the expression sir a lot, didn't really think about it. So thank "Sir and/or Madam..."

Thank you*

lucidpsycho (author)2015-02-24

I've seen this happen whenever I make sheera syrup for gaimat dumplings.

It crystalizing?

Yes when the sheera doesn't have enough water or lemon juice in it, it starts crystallized around the stirring spoon and the sides of the pot

memartina (author)2015-02-26

Why would someone go through so much trouble and risks to make a string of rock candy? I don't know, so I'm asking.

Do you like Glazed donuts, Deep Fried food, Or hard cady..?

guds777 (author)2015-02-26

Next cook Meath. Blue Meath.

guds777 (author)guds7772015-02-26

Just for clarification that was a joke...

TrollFaceTheMan (author)guds7772015-02-26


Viliuks (author)2015-02-26

The thing is I see they don't grow as normal crystals that take weeks, they are hard and it seems these are soft crystals. Correct me if I'm wrong. :)

TrollFaceTheMan (author)Viliuks2015-02-26

Depends on what you mean by "Soft", the crystal sizes are indeed smaller as they are forced to grow really fast, but they still are as Crunchy Good as can be.

You can still grow the crystals very fast and get them to be big too, by either using bigger seed crystals, or simply not heating it as much (Example 220F instead of 230F.)

That will also of course cause them to grow slightly slower, which is as to why they'd be bigger.

kriemer (author)TrollFaceTheMan2015-02-26

Have you ever experimented with temperatures vs time vs crystal size, i.e. 230F vs 220F, vs. 210F, vs 200F, etc? How cool can you go and still get a rapid crystallization? As a rock candy lover from way back, part of the "WOW" factor (for me) has always been the size of the crystals.

Great winters day science project with a taste treat reward at the end to the experiment. Wonderful that you added the science to the instructions.


TrollFaceTheMan (author)2015-02-26

Good luck!

johnnyoh (author)2015-02-26

I am going to do this with my neighbor's kids. But I prefer them fried.

TrollFaceTheMan (author)johnnyoh2015-02-26


TrollFaceTheMan (author)2015-02-25

Thanks for all the support, and if you like it please vote for it <3

bucklipe (author)2015-02-25

I'm going to do this with my grandkids.
Not boil them... Make them some rock candy.
Two ideas when I do it:
Instead of string, I'll use a bamboo skewer suspended from more skewers laying across the jar.
I will use Sanding Sugar (largest crystals) to seed the skewer.
The Sanding Sugar is a bigger crystal and would make larger crystals on the skewer.

TrollFaceTheMan (author)bucklipe2015-02-25

Very nice, if you get a chance please post some pics!!

zaphodd42 (author)2015-02-25

Great project! I'm always looking for Maker Day stuff with my 5 year old niece. Quick results, a ton of science and candy at the end of it all! What doesnt say "kid friendly" about it! (And I'm sure her mother will love her eating 4 cups of sugar and coming home from her uncle's house!) Thanx for the idea!

It's kid friendly so long as there is a responsible adult there. :)

Best of luck!!

Raitis (author)2015-02-24

Ooooh, this is really fast! Thanks for posting.

TrollFaceTheMan (author)Raitis2015-02-24

No problem, thanks for commenting!

tomatoskins (author)2015-02-23

I've always loved everything about rock candy crystals in general! Great instructable!

Thank you very Much :)

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Bio: I am just a person who loves doing crazy and fun things... I always love to try to innovate when I can, and share any ... More »
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