Every morning at the breakfast table, the honey flows slowly from the spoon onto the roll and paints a kind of zigzag pattern on the butter when you slowly move the spoon in one direction. But where does this zigzag pattern come from? The phenomenon can often be observed in the home: when we put the pancake batter in the hot pan or forcefully squeeze the mustard from the tube onto the sausage. And the confectioner is happy about the effect when he decorates the cake with liquid chocolate. The tough mass always folds back and forth in a zigzag as soon as it hits its base. The phenomenon is so commonplace that hardly anyone thinks about it, let alone wonders.
Nevertheless, scientist Neil Ribe from the Institut de Physique du Globe in Paris asked himself why. He developed a model for the folding of viscous liquids. Various parameters such as the initial thickness of the liquid film, pouring speed, drop height and properties of the liquid - for example viscosity, density and surface tension - are included in the equations.
And indeed: The model developed by Ribe can predict how a liquid will behave under the respective experimental conditions and how often it will fold back and forth, whereby Ribe distinguished between two different types of folding – the " forced" and the "free" convolution. The mustard tube, for example, falls into the first category: the mustard is highly viscous and has to be squeezed out of the tube so that it flows at all, whereas the honey runs down from the spoon by itself, i.e. with the help of gravity. Here free folding occurs. Laboratory tests showed that the predicted flow behavior corresponded well with the experiments actually observed. And what's the point of all this?
For example, pastry chefs could calculate how to create an ideal pattern of chocolate on the cake. Joking aside, this theory sheds light, among other things, on the movement of layers of rock deep inside the earth. For example, rock that submerges into the earth's interior, although it appears to be solid, shows a kind of flow behavior - but viewed on a time scale of millions of years. The food industry could also use this new model to optimize the filling of packaging with viscous foods - which brings us back to honey.