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Chocolate, though sweet and delicious, is a pain in the neck to pump. It’s shear sensitive, viscous, solidifies when cool, and also requires special attention to hygiene (as it is for human consumption). If you’re building a new system or troubleshooting an existing one for chocolate transfer, take a quick read through these common pitfalls to avoid when it comes to pumping this sweet confection.
To avoid burning the chocolate, it’s critical to keep the cocoa butter in the chocolate as a homogenous mixture. Chocolate is shear sensitive, and cocoa butter and cocoa solids can easily separate if pumped at high speeds. For this reason, centrifugal pumps are generally a poor choice for chocolate transfer applications.
Don’t forget to watch your discharge pressure too. If the pump is going against 100 psi or more, shear will amplify inside the pump, separating the cocoa butter, and burning the chocolate. Pump as slow as possible with highly viscous chocolates to prevent this from happening.
Slower pump speeds relate to lower NPSHR (Net Positive Suction Head Required). This is critical for viscous media to pass through the suction of the pump. Generally, you’ll want to keep the RPMs below 300 to give proper consideration for viscosity.
If chocolate cools, or solidifies during a shutdown period, it is critical that the chocolate is warmed before start up. Significant damage occurs during a cold start with chocolate in the pump.
It’s a good idea to choose a pump with a jacketed feature that allows for circulation of hot water or steam through the pump (without coming in contact with the chocolate).
Avoid trying to warm the chocolate by means other than a jacketed pump. Utilizing a heating torch, or other methods of direct heat, can burn the chocolate.
There are a number of reasons centrifugal pumps are a poor choice for transferring chocolate. First, Centrifugal pumps run at faster speeds, imparting far too much shear on chocolates. They also don't deal with viscosity well, as described in our previous post, Why Viscous Fluid Is The Centrifugal Pump's Kryptonite, efficiency and production takes a nose dive when viscosity increases from 0 cps. On the other hand, flow rate and efficiency increases as viscosity increases with positive displacement pumps. They're also a much better choice because they operate at low speeds (less than 300 RPM is typically recommended for chocolate). Depending upon your goals, a gear pump, rotary lobe, or circumferential piston pump are excellent choices for chocolate.
A gear pump offers easier, faster maintenance, given its single shaft seal. Lobe or circumferential piston pumps are more complex, with two shaft seals, but offer some solids handling capability for chocolates containing ingredients like peanuts, or raisins.
Choosing the right materials of construction for a pump that transfers chocolate is tricky. Some important questions that need to be answered are:
There are some basic guidelines to follow when pumping chocolate. These include:
Not following these guidelines can result in pump failure, prematurely worn parts (idler pin, bushing, sometimes the crescent or rotor gear), and destroyed mechanical seals (if used).
Chocolate is one of the most difficult fluids to transfer in food production. With its ever changing and shear sensitive properties, it must be handled with extreme care. If you’re struggling with consistency and quality of your chocolate, talk to an engineer experienced in the subject. They’ll be able to help you make changes to increase production, and reduce chocolate induced headaches.