A Chemist Explains the Science Behind That Viral Freezing Grape Video

Several days ago, a strange video emerged on Reddit involving a grape and a glass of cold water. A user who goes by the name u/Rollertreatment shared footage of the phenomenon, in which a person (who goes unidentified) dips a grape, which appears to be frozen, in a glass of water. Ice crystals spontaneously begin to grow around the grape, forming a gorgeous snowflake-like sphere.

Commenters on the post offered several vague explanations for the surprising display: One suggested that the water had been chilled to around zero degrees (but was not allowed to freeze), creating a state called “metastability.” When the grape hits the water, it adds energy to the cup, and the water immediately freezes. Another postulated that the grape caused the molecules in the water to “line up,” and as a result, the water quickly formed frozen crystals around the grape.

None of these descriptions sound exactly scientific, so we decided to get a straight answer from an expert: Dr. Laura Kaufman, a chemistry professor at Columbia University.

Turns out the grape doesn’t need to be frozen for this experiment to work. Dr. Kaufmann told Kitchn that the grape is being submerged in a glass of “supercooled water,” in other words, water that is below its normal freezing temperature of zero degrees Celsius.

“A supercooled liquid is metastable. It’s not the lowest free energy state of the substance at that temperature (which would be a crystalline solid), but it can exist [in liquid form] if it is undisturbed.”

You don’t need a science lab to supercool water, but you do have to cool it very fast and in a totally clean container, which might be tricky in the average household, which is full of dust and dirt particles (if you want to try it, here’s an instructional video).

Crystallization (or freezing) of the water can only happen when the molecules are able to “come together” in a certain order; those organized molecules are what ultimately cause the crystals around the grape to form, Dr. Kaufman adds. If the molecules don’t have anywhere around which to “become ordered,” like a speck of dirt or a crack in the glass (again, that’s why it’s important that the water glass be totally clean), the crystals won’t start to grow. However, if you introduce any object to the supercool liquid — like a grape — it acts as a catalyst for the crystals to begin to form.

“[The grape] is perturbing the system, and introducing an entity around which molecular ordering can happen. The crystal nucleates and starts to grow. The particular shape of the grape then supports the growth of the ice as a sphere,” she says.

So there you have it. There’s no magic at work here in this interaction between cold water and breakfast fruit — just a simple chemical reaction. Does that make it any less cool to watch happen? Not at all. Although the explanation might be simple, this video does prove that nature is strange and beautiful, and full of fun tricks that you can experience even from the comfort of your own kitchen.