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Problem

In the early stages of chocolate refining, cocoa beans are ground to a pulp called cocoa mass, which is prone to rapid biological degradation. This is avoided by pasteurising the cocoa mass shortly after the grinding operation. The cocoa mass is a viscous non-Newtonian slurry with high solids content making it extremely difficult to process.

Traditionally, chocolate manufacturers have used stirred tanks with steam heating coils to raise the temperature of the cocoa mass which is then held for a predetermined period of time to complete the pasteurisation. This is a batch operation involving large tanks with expensive agitators. Rapid buildup of cocoa mass on the steam coils results in very low heat transfer coefficients and an expensive cleaning stage between batches. Residence time control is poor.

Solution

Statiflo was approached to determine whether static mixing technology could solve some, if not all, of the Chocolate Refining problems. Following close consultation with the customer, Statiflo engineers quickly designed a custom engineered total process solution.

The heating stage was performed by direct steam injection using a small diameter Statiflo Motionless Mixer to ensure rapid dispersion of steam to avoid the noise and vibration normally associated with inline steam injection. Due to the completely mixed flat temperature profile, steam injection rates could be controlled by downstream temperature sensors.

Having raised the cocoa mass temperature high enough for pasteurisation to occur, it was then essential to provide sufficient residence time to complete the process. This was achieved by several stages of large diameter Statiflo Motionless Mixers, designed to provide ‘plug flow’ for the specified residence time.

The complete package included Statiflo Series 200 Mixers in sanitary stainless steel construction complete with all injectors, reducers and interconnections.

Result

This system has now been running for over 15 years and has been successfully duplicated on other chocolate refining processes. The original batch operation was superseded by a continuous inline process. Tanks and agitators, together with their heavy maintenance, their high energy consumption of steam and electrical power, and their labour intensive cleaning requirement were made obsolete.

Continuous pasteurisation 24 hours per day, 365 days per year at very high heat transfer coefficients and with excellent control of residence time has been possible.

STATIFLO MOTIONLESS MIXER FEATURES OF PRIMARY IMPORTANCE IN THIS CASE STUDY

  • Approaches ideal plug flow for residence control
  • Efficient heat transfer in laminar flow
  • Degree of mix independent of viscosity and flowrate
  • No moving parts for maintenance free operation
  • Sanitary design in polished stainless steel
  • Suitable for cleaning in place (CIP) systems
  • Consistent and predictable performance
  • Completely sealed system

Other Statiflo Features

  • Minimal space requirement
  • Available in all sizes
  • Eliminates radial gradients
  • Available in any material
  • Custom designed
  • Meets all QA/QC levels
  • Available worldwide

 

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