Measuring this feature of materials makes a difference from start to finish
More features of food impact its appeal than might be apparent. One of them is viscosity. In general, something with more viscosity is like it sounds—thicker—but there’s more to it. Scientifically speaking, viscosity “is a measure of the resistance of a fluid to deform under shear stress,” according to BYK (Columbia, MD and Geretsried, Germany) in its introduction to viscosity, adding: “Viscosity describes a fluid’s internal resistance to flow and may be thought of as a measure of fluid friction.” In food testing, viscosity is measured to assess flow and texture for quality assurance and more.
Virtually any and every food and food-processing step depends in some way on viscosity, and there several comparisons to make. Bakerpedia.com, for instance, provides a useful example: “Water would have a lower viscosity than cake batter.”
Beyond the various ways to use viscosity in food testing, these characteristics can also be reported in more than one way. In the United States, viscosity is often given as centipoise (cP), and the metric measurement is millipascal (mPa), where 1 cP = 1 mPa * s.
However viscosity is measured, it’s a must in the food industry.
Texture technology
People often say that they don’t like a food because “it’s a texture issue,” not necessarily because of the taste. That texture depends on viscosity.
How a material—food or beverage—is handled can impact its viscosity. For example, processing often includes pumping the material through pipes and heating and cooling, and these processes can change a material’s viscosity. The change, however, depends on the specific materials and the details of the processes. Overall, though, the food and beverage industry tries to maintain a product’s desired viscosity all the way to the consumer.
To accomplish that, food and beverage manufacturers must know the viscosity of the starting components, the impacts of processes on viscosity, the desired viscosity of the final product, and how that viscosity holds up on the way to the consumer.
Beyond testing the viscosity for the ultimate quality and texture of a product, food and beverage manufacturers track this metric throughout processing for other reasons. For example, a material’s viscosity affects how efficiently it moves through manufacturing steps, such as flowing through pipes. That efficiency of processing plays a part in the cost-effectiveness of making a product. In fact, the viscosity of a product’s components, intermediates, and the final food or beverage must be measured and controlled. The viscosity, for instance, determines how fast a material can pass through pipes in a manufacturing facility. If the steps to making a food involve heating or cooling, viscosity impacts that. Even the speed of packaging a products depends on the viscosity.
As a result, viscosity must be measured and considered when designing the manufacturing process for a product. Knowing the viscosity of the product at various stages of preparation is critical to designing an efficient process. The types of pipes used and the geometry of the entire system must be optimized for the physical features, including viscosity, of the material flowing along the production line. The structure of the production line, the steps, and the material’s viscosity also determine how much force needs to be added to keep everything moving at the right pace, even placing the food or beverage into its packaging.
According to a study on the viscosity of ketchup in the Journal of Food Engineering in 2016, “The viscosity and shear thinning behavior are essential characteristics of tomato ketchup. … “A real-time monitoring of those characteristics during processing is important to obtain a good quality of the final product and to reduce production waste” (Berta, M.; Wiklund, J. et al. Correlation between in-line measurements of tomato ketchup shear viscosity and extensional viscosity; doi: 10.1016/j.jfoodeng.2015.10.028).
Getting that good quality, though, can require some additives or adjustments to a recipe.
Tweaking the texture
No matter how much work goes into the design and implementation of manufacturing a food or beverage, changes occur and adjustments must be made. Even cultural changes can drive the need to adjust viscosity. In 2018, for example, in the Journal of Food Science, researchers reported: “There is a growing interest in substituting animal proteins with plant protein sources in food systems.” As an example, they explored replacing egg-white (EW) protein from chickens with hydrolyzed wheat gluten—gluten hydrolysates (GH)—to foods like meringue that are foamy, and the gluten worked better. The team noted, “the greater foaming capacity of GH than of EW protein solutions was related to their superior meringue batter (density and apparent viscosity) and product (specific volume) properties” (Wouters, A.G.B.; Rombouts, I. et al. Enzymatically hydrolyzed wheat gluten as a foaming agent in food: incorporation in a meringue recipe as a proof-of concept; doi: 10.1111/1750-3841).
In processing, viscosity can also be adjusted. “Rheology additives are generally suitable for increasing system viscosity—and thereby for improving storage stability, processability, and achieving greater film thicknesses,” notes the BYK website. For food and beverage applications, a rheology additive should comply with the necessary regulations, such as those from the U.S. Food and Drug Administration (FDA) or the European Union (EU).
From concept to consumer, viscosity matters in foods and drinks. The more viscosity is considered and measured, the more a food or beverage’s features can be controlled and maintained. From design and development to manufacturing and delivery, scientists and process engineers can make use of a food or beverage’s viscosity to improve the process, the product, and the production line’s efficiency and finances.
Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]