Brookfield Engineering

Chocolate

Process Viscometer Application Data Sheet

Application

Chocolate processing, a major segment of the food industry, is a primary application market for process control. The Brookfield TT-200 Process Viscometer provides on-line monitoring of viscosity in the formulation (coating and molding) of fully melted chocolate. The distinct advantage of the viscosity measurements made with the TT-200 Viscometer is that it can be configured to duplicate the measurement of the Brookfield laboratory viscometer which is used to define the behavior characteristics of chocolate. This guarantees reproducibility of viscosity measurements between lab and process.

Problem Description

Various chocolates with different flow properties are used for enrobing and for making blocks. It is common to describe the flow property by the Casson flow curve, which incorporates the following two parameters:

  • Yield value is the shear stress which must be exerted to initiate flow. It relates to the coating or decorating characteristics.
  • Plastic viscosity is a function of the shear stress which must be exerted to maintain constant flow. It determines how well the chocolate will flow into a mold.

The objectives in chocolate processing are:

  • To assure a uniform flow rate for enrobing (covering an object like a nut or piece of fruit).
  • To assure a uniform flow rate for block making.
  • To assure consistent product.
  • To assure compliance with industry standards.

To meet the Chocolate Manufacturer's Association and National Confectioner's Assocation standards, chocolate manufacturers demand proper coating characteristics (as measured by yield value) and proper flow into molds (as measured by plastic viscosity).

Solution

The accepted method in the United States for assuring uniform flow rate for chocolate processing is to use Casson geometry to determine flow curves. Brookfield gives chocolate manufacturers the necessary equipment to reproduce these industry-standard Casson yield values and plastic viscosities, both in the laboratory and on-line for the chocolate formulation process.

To measure the Casson values, it is necessary to take viscometer readings at different speeds in order to evaluate shear stresses against different shear rates. This evaluation is initially done in the laboratory utilizing a Brookfield multi-speed viscometer with a constant temperature bath and a special Casson geometry-configured Small Sample Adapter. Calculations are carried out to determine the plastic viscosity and yield stress values. These measured values are used to define process viscometer set-points for on-line process control. Examples include the addition of cocoa butter and two-chocolate blending to obtain the desired flow properties of melted chocolate.

The TT-200 Viscometer provides accurate, continuous on-line viscosity measurement because:

  • The coaxial cylinder geometry permits accurate mathematical definition of the shear rate and duplicates the geometry of the bench-top viscometer used to make the lab viscosity measurements.
  • The TT-200 Viscometer measures viscosity values on-line that insure compliance with the Casson flow curve.
  • The TT-200 is a fixed shear rate instrument with a linear output which provides high sensitivity to variations in viscosity.

By controlling viscosity in process, the manufacturer maintains a constant and uniform chocolate flow.

Qualifying Your Application

  • How frequently are you checking the chocolate for viscosity?
  • How often are you making viscosity adjustments by modifying the batch formulation?

If any of the above checks or adjustments occur every 15-30 minutes, on-line process viscosity measurement is recommended.

Benefits

  • Decreases the time for certifying batches meeting specification.
  • Reduces time-consuming sample grabs.
  • Duplicates same tests on-line as off-line in the lab, thus minimizing variations from established standards.
  • Can provide a complete production record for later review.
  • Helps maintain constant and desired flow properties for each batch of chocolate.
  • Provides assurance against rejected chocolate.

Viscometer Specifications

  • Viscosity Range: Defined by test data from lab viscometer
  • Temperature Range: 300°F maximum
  • Pressure Range: 200 psi maximum
  • Repeatability: ± 0.5% of span
  • Signal Output: 4-20 mA
  • Mounting: 4” 150# flange including TT-200-52HY modified outer baffle for chocolate service
  • Motor: Single-speed synchronous; multi-speed available
  • Power Requirement: 115 or 230 VAC; 50 or 60 Hz
  • Electrical Code: NEMA 4; (water & dust tight)
  • Rotating Shaft Seal: Food grade teflon stuffing box
  • Material of Construction: 300 series s/s wetted parts

References

Available upon request

Return on Investment

Typically, a 10-15% time savings per chocolate batch can amortize the equipment cost in less than one year. Use of the Brookfield TT-200 Process Viscometer:

  • Reduces grab sample and lab test times by as much as 50-100%.
  • Reduces the hold times needed for corrections to batches.
  • Can increase production up to 15% by increasing the number of batches of chocolate per day with no increase in overhead.