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Is Consistency Viscosity? Not really!

 

We make the Bostwick Consistometer. The Bostwick is used extensively to measure the consistency of sauces and condiments. It has strong application in the quality control departments of ketchup and mustard producers. Results from a Bostwick Consistometer have been used for more than six decades to control the quality of many of the foods you use.

The Bostwick has application in may other industries. More than we even know about.

However there is an underlying question. What is consistency? There have been many attempts at the answer among test and measurement people. In trying to get a good definition we started with the dictionary which defines it in three contexts which are :

  1. Compatibility among things.
  2. Uniformity.
  3. Degree of firmness.

For our purposes we have chosen the third context — Degree of firmness. I think as it relates to testing of liquid materials, the most easily understood is. “Consistency is the relative ability of a sample to flow.”

By the way I would love to learn about other definitions that make sense to you.

For many products attempts have been made to relate Bostwick Consistometer results to viscosity. There has been only limited success in a narrow ranges of flowablilty and temperature. Some reasons given by the researchers are that surface tension and density changes caused by temperature, change the correlation of Bostwick results and viscosity.

The cement and concrete industry also use the concept of consistency. They use consistency measurements to correlate to workability. That test is frequently done using a device called a slump cone.  As with the Bostwick, there are no absolute or widely accepted standards for the properties measured by this consistency test.

In summary, the Bostwick Consistometer is a critical quality control instrument for many processes. However, a dilemma is caused by not having an absolute standard for the measurement. This test is in the truest sense of the word, an empirical measurement.

Let us hear your comments and opinions.

Art

Check out this great infographic:

 

Consistency vs. Viscosity

 

by Art Gatenby

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