Quality Control in the Food and Beverage Industry is only Possible with Rheology

The last time you spread cream cheese on a bagel, did you note how easy (or difficult) it was to spread? Do you routinely shake your salad dressing to re-mix the separated oil and vinegar? In both cases, the shelf stability, dispensing and texture of your meal have been ensured through the core fundamentals of rheology.

This scientific discipline merges principles from both physics and chemistry to study the ways in which materials deform and flow under varying levels of stress. In food production, underlying rheological behaviors are critical for maintaining quality, customer satisfaction, and consistency.

Rheology is the study of materials’ flow and deformation, used to predict a product’s behavior and optimize formulations. For food and beverages, rheometers measure and quantify how a product responds to being stirred, squeezed, spread or shaken; how it changes when heated or chilled; and even how it is perceived when consumed.

Rheology is a must-have tool for ensuring quality across new products or reformulated ones. Food formulations change for various reasons, such as: accommodating a supply chain issue with a specific ingredient, expanding to offer a new flavor, adding a plant-based or health-conscious alternative, or changing to eco-friendly packaging that affects product dispensing.

Whatever the reason for your new product or formulation, its rheology must meet consumer expectations for it to be commercially successful. The final product will need to achieve attributes like:

• Enticing appearance – not too runny, not too lumpy
• Desirable texture and mouthfeel, not to “thick” or “thin”
• Smooth dispensing, easy to pour or squeeze or spread, and no drips
• Shelf stability throughout its time in transportation, store shelves, and customers’ kitchens

After successfully developing or reformulating a product, food manufacturers must then produce it on a large scale. Variations in the raw ingredients or in the processing conditions can result in batches that fail to meet consumer expectations or even trigger costly recalls. Integrating rheological measurements into quality control testing at production sites ensures a product is consistent and avoids consumer dissatisfaction long before it even gets out of the factory.

For quality control managers in food production facilities, data from rheology will help answer questions such as:

• Is our product consistent across different batches over time and throughout different regions?
• Has product consistency changed with the addition of new equipment or ingredients?
• How much variation in viscosity or yield stress should we deem acceptable before a batch is rejected?

With any food product or beverage, you’ll need four key measurements to understand how that product behaves during production, transportation, or consumption.

Viscosity: This describes a material’s resistance to movement. Viscosity exists on a continuum from thick (honey) to runny (cola). However, many foods and beverages are non-Newtonian, meaning their viscosity changes under shear. In many cases, this change is by design (e.g., a market shift to squeeze-bottle packaging for condiments such as cream cheese or mayonnaise).

Shear thinning: Some foods that remain viscous at rest will become quite runny when chewed, stirred, shaken, or spread. For example, peanut butter is dense and thick when sitting in its container but mixing makes it softer and more spreadable

Yield stress: Some food products change viscosity at a minimum stress level. For example, if you turn an open container of ketchup upside down, the ketchup may remain in place depending on its original consistency. Yet, if you apply pressure to the container by shaking or squeezing, the ketchup’s particles break apart. This allows customers to more easily distribute ketchup onto their burgers or fries.

Thixotropy: This describes how a product may at first decrease viscosity when under stress but then regain its structure when the stress is removed. Low-thixotropic foods regain their original structure quickly, whereas high-thixotropic food products do so more slowly. How quickly a product returns to its original state can make a huge difference in both batch consistency and customer satisfaction. A material with zero thixotropy like mayonnaise regains its structure instantly, while a high thixotropy food like yogurt can take multiple days to rebuild its viscosity after mixing.

Temperature, pressure, shaking, stirring, and other factors can affect your product’s texture, mouthfeel, and performance. These disturbances can intentionally (or mistakenly) permanently change the product’s behaviors at every stage of its life cycle. Using rheology is critical in these four key areas to ensure quality from development to the store shelf to the kitchen table.

We all know when a food product feels slightly off, but how do you measure it? Rheology allows food quality control managers to quantify and define the properties they want in their product. By setting a required viscosity, shear thinning behavior, yield stress, and thixotropy, you can ensure that your product is the same every time.

Rather than relying solely on costly and time-consuming consumer panels, food production labs and manufacturers can leverage rheology to verify batch consistency or measure the impact of formulation changes. Rheological data can even be correlated with consumer panels to predict customer satisfaction without ever leaving the lab.

Supply chain disruptions, new regulations, or small improvements in taste and texture may prompt you to tweak a formula during commercial production. Rheological measurements will help you better understand how changes to thickeners, stabilizers, and other ingredients affect the overall product’s texture. These measurements will help you determine whether the evolved formula remains within an acceptable, predictable range of measurable parameters.

Those same measurements may also require you to change the process and equipment used during production. If, for example, you introduce a new low-fat cream cheese whose ingredients have a different yield stress, you may need mixing and filling equipment capable of exerting different forces.

By running quick batch-to-batch quality control checks, rheological measurements help you feel confident that the last product to come off the line on any given day will deliver the same quality as the first. Minor, often unseen, variations in the manufacturing process can have an outsized impact from one lot to the next. If, for example, a material is under-mixed in processing, it might not achieve the right properties for the final product’s texture.

Finally, you want to ensure that the properties you worked so hard to develop in the lab are the same ones your consumer experiences on their plate. And even if it tastes delicious and is safe to consume, its behavior from container to table will impact overall enjoyment. For example, canned gravy needs to maintain enough viscosity to “cling” to meat even when it is heated.

A sensitive measurement from rheology helps you identify potential issues before they become bigger problems that can escalate into costly recalls or disappointed consumers abandoning your product. Implementing QC rheology checks before products leave your facility gives you the information to take proactive corrective action before issues occur.

To gain this vital knowledge, quality control managers use on-site rheometers like the Discovery Core Rheometer.

This instrumentation can help you understand how suspensions, gels, emulsions, pastes, and other non-Newtonian food products change under different conditions. Key features of the Discovery Core Rheometer include:

1. The ability to capture a complete viscosity profile of your products under a range of real-world storage and use conditions.
2. An easy-to-use touchscreen, complete with instructions and illustrations, that lets you perform routine measurements without a PC or advanced training.
3. A compact design that requires 75% less bench space than other models.
4. Customizable methods that can incorporate every step of your procedure and instantly indicate Pass or Fail readouts based on your specifications.

To learn more about how a rheometer works, watch this product demo.

There’s no getting around it. After your product leaves the plant, it will face a range of stressors. It may be heated or chilled, gently folded or pureed, spooned or spread, or slurped or chewed. To ensure your food product delivers consistent results across these varying environments, it’s critical to understand deformation and flow.

Only the principles of rheology – and the instruments that measure it – can quantitatively guarantee that you’re consistently delivering the high-quality products your customers expect.