Butter and Margarine

USE

Butter and margarine viscosity are extremely high. Force measurements can be used for these tests using a Texture Analyzer. Flow properties can also be measured using a Viscometer or Rheometer. The Brookfield RST-SST (Soft Solids Tester) can measure the flow properties with a test running under 60 seconds.

TEST EQUIPMENT

Instrument: RST-SST Rheometer

Geometries: VT-10-5 (10 mm long by 5 mm in diameter) and VT-20-20 (20 mm long by 20 mm in diameter) vane spindles

Test: Controlled shear rate (CSR) yield test:

• Start: 0.5 RPM
• End: 0.5 RPM
• Length: 30 seconds to 60 seconds (depending on the sample)
• Readings: 30 to 60 measuring points depending on the test length
• Temperature: All samples (and the rheometer vane spindles) were conditioned in a refrigerator at 4.5°C prior to testing.

Results

Figure 1 plots shear stress vs. time for 4 different samples. The yield value is described as the peak shear stress value (i.e., ~12,000 Pa for the sample labeled “spread”, or ~95,000 Pa for the sample labeled “Butter”). The test detects large differences between the samples.

We also calculate the modulus (slope of the stress/time curve) and again values show significant differences; ranging from1,168,313 Pa for the butter (the highest) to 75,264 Pa for the spread (the lowest).

• The combination of yield value and modulus correlate with butter “spreadability”.
• The test is done at refrigeration temperatures, where consumers are using the product.
• The test is fast; in all four tests run time was less than 30 seconds.
• The SST is a very robust instrument, able to withstand constant use in a busy QC lab with very little service.