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Why honey sticks to the spoon

honey dripping

The way molecules move in honey is like how cars move in a traffic jam. Molecules can change lane but not move forward very far (Source: iStockphoto)


Sugar molecules do and don't slow down the water molecules in this viscous fluid, according to an international team of researchers. It just depends on who you ask.

Australian researcher Associate Professor Glenn Hefter of Murdoch University in Perth and colleagues report how in the Journal of Chemical Physics.

Honey and other syrups are basically water containing high concentration of sugars.

Some researchers say that such fluids are sticky because sugar molecules slow down the water molecules, says chemist Dr Ian Larson of Monash University in Melbourne.

But others say there's no evidence for this.

Hefter and colleagues set out to settle the debate, using salt in place of sugar, which behaves in a similar way but is easier to study.

The researchers looked at two types of water molecule movement: translational motion, or movement from A to B, and rotational motion, or spinning on an axis.

They found that in syrup-like solutions, translational movement of water molecules slows but rotational movement is unaffected.

Larson says this can be likened to what happens to cars in traffic jams.

Cars might be able to change lanes (rotational motion) but can't move forward (translational motion).

Larson says the contradictory findings in previous research are not contradictory at all.

He says they are a result of different researchers measuring different kinds of water molecule movement.

"Depending on what type of experiment you do, you can either measure rotational motion or translational motion," he says. "Everybody's right."

Tags: food-and-cooking, chemistry, physics