Growing sugar crystals makes a fun and delicious science experiment for children.
The kids and I really enjoyed growing sugar crystals this past week, and the kids especially loved eating them! This is a science experiment that we had been meaning to do ever since we grew salt crystals, but it took us a couple of years to get around to it!
Delicious Science: Growing Sugar Crystals
To make the sugar crystals, we boiled as much sugar as we could in a cup of water. I didn’t measure, but we had close to three cups of sugar in that cup of water – it was a very thick syrup! We were careful to keep the heat high enough to dissolve the sugar, but low enough not to caramelize it. The sugar syrup is still a light brown because we used raw sugar, which is a brown color to start with. We added a dash of vanilla, too, just for flavor since we were basically making candy.
Once the sugar was dissolved, we hung a bit of yarn over the edge of our jars, covered the jars in clean cloth kleenex, and kept everything together with the round screw-top. It’s important to keep just a cloth or paper towel over the top of the jar so that there is ventilation but the syrup is protected from dust. You also want to make sure some of your yarn is hanging over the edge so that you can easily pull your crystals out at the end. Then we set them on the shelf for what was meant to be a week but turned into 10 days because we forgot about them at the end.
Update: My friend Natalie tells me that having the yarn touching the edge of the jar probably kept crystals from forming. So, if you want to crystals to attach to the yarn, you need the yarn to attach to something else (say, a popsicle stick or even another piece of yarn) that stretches across the top of the jar. I do remember my mom using yarn with a paper clip to weigh it down tied to a popsicle stick that sat across the top of the jar when we made these when I was a kid. Natalie had the best luck using wooden skewers to grow crystals. Mommy Crusader shares great tips for making skewer rock candy!
I had expected the crystals to grow along the yarn, but instead they grew across the top of the syrup – but still attached to the yarn. I don’t know if they did this because the jars we used were so shallow, or if that just happens a lot anyhow. The important thing is that the crystals grow, not how they grow.
Two of our jars were covered in crystals, and two only had a few. I suspect that the two with only a few crystals got moved around a little bit too much by curious children.
Even though our crystals didn’t grow the way I expected, the kids were still able to pull most of them out by the bit of yarn we left hanging over the edge. The three older kids really liked this candy, but two-year-old Anna declared that it was “Ew.” That’s fine with me.
I was really excited to see how clearly the crystals formed! There were a few on their own that I didn’t manage to photograph at all, and then these clumps that I got okay photos of.
I was fascinated by how clearly the shapes of the crystals could be seen (that’s a paper towel they are sitting on, for scale reference). Even though I didn’t take a close-up when we grew our salt crystals, it is obvious that these sugar crystals are asymmetrical while the salt crystals were much more cube-like.
Have you ever grown sugar crystals? How about salt crystals?
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Snackable Science is another great edible science resource for kids:
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MaryAnne is a craft loving educator, musician, photographer, and writer who lives in Silicon Valley with her husband Mike and their four children.
SO cool!
Wow! You really succeeded in growing tremendously large crystals!! I will have to try this at home with my kids. They will love it! Thanks!!
The crystals were really neat to look at! Much larger than our salt crystals.
Wonderful photography, MaryAnne! What a fun science experiment for kids.
Thank you, Elisa! I was so happy to get photos of these beautiful crystals.
We did this when my oldest were little, but have had bad experiences with it since then…not sure why. Your adding vanilla has got me wondering if the vanilla would join with the sugar in the crystals and change them, or just flavor them…or just evaporate off…hmmm…I think we might have to give this a try :)
I think the vanilla flavored them, but didn’t do anything else. The crystals definitely looked like regular sugar crystals to me.
I have never successfully grown crystals. I don’t know why, but for some reason I just am not successful with it. Actually I can come up with several reasons why.
I was so glad these worked, because a lot of my friends have tried unsuccessfully. I did some reading before that really emphasized having a lot of sugar in the water – as much as possible.
We also did it once a couple of years back. My husband had to experiment because we had the same experience with the string. However, the rock candy formed well on a wooden skewer – go figure!
How interesting! Maybe we will try a popsicle stick next time.