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Brookfield AMETEK

Ketchup

Laboratory Viscometer Application Data Sheet

USE

Ketchup is a condiment or dressing. It is typically poured, "squirted" or spread onto other foods, such as hamburgers, frankfurters [or "hot dogs"], other sliced meats or poultry, French fries, and in making sandwiches, for example.

MEHTHOD #1

Test Equipment:

  • Instrument: DV-I Prime or DV-II+Pro Viscometer
  • Spring Torque Range: Various, such as RV
  • Spindle: Various T-bars, such as T-B or T-C
  • Accessory: Helipath Stand
  • Speed, rpm: Various, such as 6 rpm

* While a particular model/version may be used as an example in this method, any current or past model/version from the same series may also be used. Please consult a sales associate to discuss the most current instrumentation and software available.

The test may be run at room temperature, or at refrigeration temperatures. The DV-I Prime provides continuous measurement of both torque and viscosity. The DV-II+Pro also provides continuous temperature measurement.

The Helipath Stand may be used with various Brookfield Viscometers or Rheometers. The choice of Spring Torque Range, spindle and speed may vary widely, depending upon the ketchup. In our example, we used a Brookfield RVDV-II+PRO, with Rheocalc v3.1 software for automated instrument control and data acquisition. Representative data from the analyses are shown in Figure 1:


Figure 1: Viscosity Data for Name Brand and Store Brand Ketchup at Room Temperature

The name brand product, shown in purple, is slightly more viscous than the store brand ketchup, shown in blue. The Helipath data starts at "zero" viscosity - before the spindle drills down into the material - and climbs to a "plateau" region where the spindle is in the bulk of the sample. The system then reverses direction, and the measured torque and calculated viscosity drops to "zero" as the spindle rises up and out of the sample. The "plateau" region for both products occurs between approximately 30 and 380 seconds.

The Rheocalc data may be exported to a spreadsheet, and the plateau-region data averaged, to give a QC number for viscosity. On the other hand, the Data Averaging feature available in the Rheocalc Wizard may also be used to output averaged data values. Another choice may be to simply have the system "drill" down into the sample for a specified amount of time, say 100 or 120 seconds, and then have the operator record the viscosity value at that time.

MEHTHOD #2

Test Equipment:

  • Instrument: YR-1 Yield Stress Rheometer
  • Spring Torque Range: Various, such as RV
  • Spindle: Various vane spindles, such as V-73; immersed to the primary immersion mark
  • Speed, rpm: 1 rpm

* While a particular model/version may be used as an example in this method, any current or past model/version from the same series may also be used. Please consult a sales associate to discuss the most current instrumentation and software available.

The test may be run at room temperature, or at refrigeration temperatures.

The choice of Spring Torque Range, spindle and speed may vary widely, depending upon the "thickness" of the ketchup. We used the Brookfield RVYR-1 Rheometer with EZ-YieldTM v1.4 software for automated instrument control and data acquisition. The YR-1 performs yield stress tests. The yield stress may be defined as the stress that must be applied to make a solid material flow like a liquid. The corresponding apparent yield strain is the amount of deformation or movement that occurs before the sample structure breaks down and starts to flow.

Representative data from tests run on the same two ketchups in Method #1 are shown in Figure 1:


Figure 1: Yield Stress Data for Name Brand and Store Brand Ketchups at Room Temperature

Figure 1 shows that the name brand product has a higher yield stress than that of the store brand at room temperature, 78 Pa vs. 68 Pa. The slope of the data line for both products leading up to the yield stress is similar, which implies that the "stiffness" of both products may be the same. The name brand ketchup data are shown in blue, while the store brand data are in green. Testing with an RVYR-1, the V-73 vane spindle at 1 rpm produced on-scale results with both products. If the test were run at a slower speed, the curves would shift to the right and the slope of the data line would be less. If the tests were run at a higher speed, the curves would shift left with a steeper slope.

MEHTHOD #3

Test Equipment:

  • RS3115LS or RS3230LS
  • FTKY3 water jacket
  • CC3-25S serrated bob
  • MB3-25F sample cup
  • Software Rheo3000
  • Bath/circulator F26MA /TC-602P

There are many ways to measure tomato ketchup but the R/S-CC coaxial cylinder rheometer with a serrated bob gives very good results, testing for multiple rheological properties in one quick test.

The R/S+-CC is a rotational, controlled stress instrument using coaxial cylinder (DIN 53019) or vane geometries. The combination of high torque (50 mNm) and wide speed range (0.1 RPM to 1,000 RPM) allow the instrument to measure over a wide shear rate range (0.13 sec-1 to ~1300 sec-1).

Because the R/S+-CC will operate in controlled stress (CSS) or controlled shear rate (CSR) modes, it offers more test types than standard controlled rate instruments.

The graph, as seen in Figure 1, shows a test of three different ketchups using a program which ramped torque from 0 mNm to 10 mNm over 60 seconds, taking 60 readings. The green data set is “store brand” ketchup which was considerably thinner than the two “name brand” products, indicating that the store brand had lower % solids, and therefore less body.


Figure 1

Results

As expected, all three samples were pseudoplastic (shear thinning; increasing shear rate decreases the viscosity of the sample).

This test gives the flow properties of the fluid, but because the test ramps torque rather than speed, we can also see the yield value simply by plotting the data differently, as seen in Figure 2.


Figure 2

When torque (or shear stress) is ramped from 0 to a higher value, there is no shear rate or speed until yield value is achieved. In this case we can see that all three samples had no speed until ~ 11.5 Pa, therefore the yield value is 11.5 Pa for all three samples.

While we might think that ketchup should have a higher yield value (11.5 Pa being a fairly small number) if we look at the data we can see that the viscosities are quite high: even the thinnest ketchup is ~500 Pa*s or 500,000 cP at low shear rates while the thickest is 9,000 Pa*s or 9,000,000 cP. It is not just yield value that makes ketchup hard to get out of the bottle but a combination of yield value and very high low shear viscosity.

Rheo3000 also allows us to use a regression analysis of the test data, in this case using the Ostwald (power law) model:

Store Brand Ketchup Name Brand 1 Name Brand 2
Ostwald Regression y = m* x^k2
y = 35.9435* x ^ 0.2804
x ... Shear Rate[1/s]
y ... Shear Stress[Pa]
Ostwald Regression y = m* x^k2
y = 59.7102* x ^ 0.2726
x ... Shear Rate[1/s]
y ... Shear Stress[Pa]
Ostwald Regression y = m* x^k2
y = 76.3444* x ^ 0.2777
x ... Shear Rate[1/s]
y ... Shear Stress[Pa]
Standard Deviation:
0.7934476899
Standard Deviation:
0.4760009051
Standard Deviation:
1.0821390927
Stability Index:
0.9989913699
Stability Index:
0.9996369965
Stability Index:
0.9981238762
Valid Data Pairs
3
Valid Data Pairs
3
Valid Data Pairs
3
Constants:
[0] 35.9435010928054
[1] 0.280408642634189
[2] 0
[3] 0
[4] 0
[5] 0
[6] 0
[7] 0
[8] 0
[9] 0
Constants:
[0] 59.7101880334478
[1] 0.272646030622011
[2] 0
[3] 0
[4] 0
[5] 0
[6] 0
[7] 0
[8] 0
[9] 0
Constants:
[0] 76.3443900463556
[1] 0.277662120606301
[2] 0
[3] 0
[4] 0
[5] 0
[6] 0
[7] 0
[8] 0
[9] 0

The model output gives us the correlation to the model (stability index) as well as the two Ostwald constants: Consistency Index (labeled constant 1) and Flow Index (labeled constant 0). The consistency Index is the calculated viscosity at 1 sec-1 in Pa*s. The Flow index is the “shear thinning” index: a Newtonian fluid would have a value of 1.0. values less than one are shear thinning, over 1 are shear thickening.