Chocolate viscosity

With Easter upon us, many of us enjoy eating the associated chocolate eggs. It’s often easy to overlook the numerous steps between cacao harvesting, transporting, processing, and ultimately enjoying the taste of the final chocolate confection. As PTG/e, we’ve provided support in one of those many steps, related to the manufacturing process of chocolate products.

One of our customers approached us for viscosity measurements on raw cacao, an intermediate product in the chocolate production process. The viscosity data was required for the pump design needed to transport the cacao through pipes from one vessel to another. To correctly size such a pump, it is important to know what the viscosity of the material is, and particularly what the range of viscosities could be at different pumping speeds and temperatures.

Therefore, we used our TA Instruments DHR-2 rheometer, equipped with a Peltier heating system, with a 60 mm parallel plate configuration. We measured the viscosity of the raw cacao over a wide range of shear rates (simulating different pumping speeds), and at different temperatures as well. An example of such a flow sweep measurement performed at 90 °C is shown in the plot below.

While at low shear rates the raw cacao has a more or less constant viscosity, it can clearly be seen that the viscosity decreases dramatically at increased shear rates. This kind of material behavior is usually referred to as ‘shear thinning’, where the viscosity decreases as the flow increases and a certain yield stress is overcome. You could compare this behavior to peanut butter, which does not flow if you tilt the jar upside down, but spreads easily once you start smearing it on a sandwich. Such information on the shear thinning behavior of any material can be very useful in process design, because less energy is needed to pump a lower viscous material of course.

With all the viscosity data we collected under various circumstances, our customer could complete his pump design and thus satisfy their customer needs.

Besides raw cacao, we have had the pleasure of measuring a wide variety of foodstuffs, such as fruit juices, bread paste and pesto. Similarly, we have had the (arguable) pleasure of measuring cattle feed ingredients as well as filtered sewer sludge. Most importantly in all cases, we were able to provide our customers with useful viscosity data in order to aid in their process design.

Interested in viscosity measurements of your fluids? Please contact us at, we will be glad to discuss the possibilities.

Happy Easter!