There’s a buzz going around the net about ice cream sandwiches not melting. It started with a woman in Cincinnati who accidentally left a Walmart ice cream sandwich out in the sun for a bit and noticed that it was not behaving the way “real” ice cream behaved.

Was this true? Watch the embedded video, but then read on for the science.

The key to the lack of melting is the guar gum added to the ice cream.

Many online comment threads are full of people decrying the use of preservatives in food, but that’s not really what’s going on here. If you look at the list of ingredients for the ice cream portion of a Walmart brand ice cream sandwich, you’ll notice some differences between that and regular ice cream you scoop out of a container. In these products (and most other ice cream sandwiches on the market) you’ll find guar gum, calcium sulfate, and cellulose gum. These compounds are the main cause of an ice cream sandwich’s startling stability.

Guar gum is a polysaccharide (a molecule made of multiple sugars) extracted from the guar bean. It’s a plain white powder that is obtained by milling the matured beans. If “natural” food is a concern for you, guar gum is about as natural as it gets. It acts as an emulsifier, which means it thickens in water and stabilizes thawing. So, of course, it’s used in many foods.

Go here to read more. Science!