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.
LACK OF CONSIDERATION FOR VISCOSITY
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.
IMPROPER TEMPERATURE CONTROL
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.
CHOOSING THE WRONG TYPE OF PUMP
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 WRONG MATERIALS OF CONSTRUCTION
Choosing the right materials of construction for a pump that transfers chocolate is tricky. Some important questions that need to be answered are:
- Which standards do you need to conform to? If your facility needs to adhere to 3-A or EHEDG standards, the lower cost, cast iron pump will not be an option for you. You will also not be able to use a pump with packing, or mechanical seals. Advise the engineer you’re working with about any standards you must meet.
- Will the pump be subject to COP or CIP cleaning? If so, you will certainly require a pump with hygienic design. Look for a pump that complies with third party certifications. 3-A and EHEDG are the two key third party certifiers in the food industry.
- Will the pump be handling products with high potential for bacteria growth (like dairy)? Chocolate generally is not a good growth medium for bacteria or fungi. But when other ingredients are added, such as the dairy products involved with making milk chocolate, hygienic pumps should be used.
NOT FOLLOWING GENERAL GUIDELINES FOR PUMPING CHOCOLATE
There are some basic guidelines to follow when pumping chocolate. These include:
- Adjusting clearances (usually extra)
- Maximum rotor rim speed of 250
- Strive to keep the discharge pressure half of the 100psi max or less
- Drilled idlers
- Casing flush or suckbacks (either holes or grooves) to move liquid to behind the rotor (In our experience, this helps with reducing burning chocolate and keeping it in a liquid state)
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.