By Mary Vessele, Global Product Marketing Manager, Test & Measurement, Cole-Parmer
Viscosity determines the quality of many foods
The last time you let a chocolate bar melt in your mouth, cut into a moist cake, poured honey in your tea, or bit into a scrumptious pizza pie, I am willing to bet you were not thinking about viscosity. You were probably not thinking specifically about quality either. All you were probably thinking about is the delicious burst of flavor and the texture in your mouth, maybe the calories as well! Quality is something we all appreciate but let’s face it, we are not thinking about the little details that give our foods the quality we expect when we are eating them. Lucky for us, the manufacturer is thinking about quality at every step of the manufacturing process and that is why viscosity is so important to them. Many factors can impact the quality of foods being manufactured. During the production process, special attention is given to measuring and tracking viscosity as it is an important indicator of quality.
Viscosity describes a fluid’s internal resistance to flow. A fluid with a higher viscosity would pour slower and seem thicker than a fluid with less viscosity. When there is a change in a material’s property such as molecular weight and density, both of which affect how a liquid flow, the viscosity changes, and the quality is altered.
Why viscosity is so important
The texture of food is dramatically impacted by changes in viscosity. The chocolate industry is particularly dependent on viscosity testing, as the texture and flow of chocolate can be complex to manufacture and maintain. The thickness of chocolate when in a melted state will impact the finished solid state. To achieve the correct density, texture, and taste of chocolate when it becomes solid, careful consideration to the viscosity of the chocolate in a liquid form is vital. After all, who wants to eat a chocolate bar with a lumpy texture instead of a smooth creamy texture?
In the baking industry, viscosity plays a very important role as it will impact the chance of phase separation, affecting the products made from batter and dough. Pinpointing and maintaining an exact viscosity when baking or working with dough ensures phase separation happens at the appropriate time during the baking process, affecting the quality of the baked goods. If a cake batter has a low level of viscosity, the phases will separate easily at the wrong time resulting in a poor-quality cake. Have you ever had a cake that is crumbly, dry or flat? So disappointing!
Viscosity testing is a tool used in the production process of just about every type of food and beverage. It is a very important test that offers repeatable and reliable results, ensuring that the quality of the product is not only achieved but also maintained from batch to batch.
Using a viscometer to measure viscosity
The most common way to measure and track viscosity is with a viscometer. Today’s viscometers are very user-friendly and functional thanks to Rotational Viscometer technology. These viscometers measure a large range of viscosity from 200 to 106,000,000 with an accuracy range of ±1% to ±0.2%. The measurement of a product’s viscosity is based upon immersing a specifically selected spindle within a sample of a product. As the spindle rotates at a specific speed, vigorously stirring to create a vortex, the torque required to rotate the spindle at a set speed is measured and is based upon the amount of drag created from the spindle moving in the liquid. Resistance to rotation is sensed by the instrument and the measured torque value is mathematically converted into a viscosity value in scientific units called centipoise (cP) or milliPascal-seconds (mPa.s). Water is the reference material that establishes the benchmark value of 1 cP for its viscosity. All materials are subsequently measured for viscosity in comparison to water. The rotational viscometer device will record and store up to 10,000 data points. With the software provided, instantaneous viewing of flow curves, plotting up to four data sets at the same time, and graphical presentation of data can be achieved. These results can be downloaded to an excel spreadsheet and the user has infinite reporting possibilities. It is very important to track batches to ensure they contain the same viscosity level throughout production to achieve optimal quality.
The flow resistance increases with the speed and size of the spindle. Different samples and materials require different types of spindles depending on how much of a sample is available, the torque range used, temperature needs, and material consistency. Thanks to the complete flexibility and configurability of today’s devices users can interchange different spindles depending on their needs. For thick more viscous samples, a parallel plate or cone spindle is used. For thinner, less viscous pourable liquids a concentric cylinder spindle would be appropriate. For gel-like material, a T-bar is an option. This is a relatively inexpensive process and many sellers of viscosity equipment offer convenient bundles in which the device, spindles, cleaning materials can all be purchased together at a discounted price.
The importance of temperature
When measuring viscosity, temperature becomes a very important player in the game because the sample will have a different viscosity measurement depending on the temperature it is at. For example, honey tested at room temperature may have a viscosity measurement much different than honey cooled in the refrigerator or heated. The test conditions to measure viscosity should be tightly controlled because temperature highly affects the results. To achieve accurate viscosity measurements the food sample should be controlled within +-05 C. To help the user maintain accurate temperatures of their samples many viscometers have built-in RTD temperature probes and will display the temperature on the unit.
It is very easy to see that Viscometers play an important role in the food industry. Viscosity is measured either in the process or at the end of processing to qualify the end product for acceptability and quality standards. Many times, samples are selected off the production floor and brought into the QC lab for testing to ensure the quality is maintained throughout the entire process.
We have made it easy for you to ensure your food and beverage products are produced with the highest of quality in every batch with one convenient viscometer bundle.
The next time you take a bite of cake or let chocolate melt in your mouth think about Viscosity!