Viscosity Testing in Chocolate. What instruments should be used?
Announcement posted by John Morris Group 22 Jun 2015
Confectionery specialists, in food processing, are continually refining processes to deliver us a better product. At John Morris, we're regularly asked about which instruments are best to apply in food processing. Happily, Brookfield have investigated viscosity applications and we'd like to share the findings with our food industry.
Chocolate is used in making a large variety of desserts and treats, including sweets, icings, pastry fillings and desserts, just to name a few.
TESTING EQUIPMENT
- Viscometer/Rheometer Spring Torque Range: HA
- Spindle: SC4-27 with SC4-13RPY Sample Chamber
- Accessories: Small Sample Adapter, TC-550AP-230 Programmable Temperature Bath
- Speed, rpm: 5, 10, 20, 50 and 100
- Temperature: 40°C
TEST METHOD
The US National Confectioners Association and Chocolate, NCA specify a chocolate test procedure using Brookfield equipment such as those listed above. The Small Sample Adapter may be used with various Brookfield Viscometers or Rheometers. We used a Brookfield HADV-III Ultra Rheometer with SC4-27 hanging link spindle for our example. The SC4-13RPY sample chamber has an integral temperature probe that connects with its cable to the rheometer, to provide temperature readout. The test temperature of 40°C was maintained by connecting the Small Sample Adapter water jacket to a Brookfield TC-550AP-230 Programmable Refrigerated Bath.
Rheocalc v3.2 software provides automated instrument control and data acquisition. It controls both the rheometer speeds and the bath temperature. Representative data from the analyses are shown in Figures 1 and 2 below:
- Figure 1: Chocolate Behavior at 40°C
Figure 1 demonstrates that the viscosity of the dark chocolate decreased as the speed increased. This behaviour is known as "shear- thinning".
- Figure 2: NCA/CMA Casson Plot of Chocolate Rheology at 40°C
Figure 2, generated in the Rheocalc™ Analysis module, compares the calculated NCA/CMA Casson model values to the measured data. The Confidence of Fit (%) or "CoF" is nearly 100%, signifying an excellent fit of the model to the data. The Plastic Viscosity is 1241 cP and the Yield Stress is 129.2 Pa. These parameters provide important measures of how the molten chocolate will flow and enrobe, for example.
The viscosity value, cP, at 20 rpm, measured with HA-range viscometer and SC4-27 spindle, correlates with Degrees MacMichael or "deg. M": deg. M = (Torque, %)x(3.40) or [(Viscosity, cP)/(250)]x(3.40). Therefore, in our example, 31.4% Torque and 7850 cP at 20 rpm correspond to 107 deg. M.
Like to find out more about chocolate viscosity? Read Brookfield's chocolate testing system