How to measure crispness / crunchiness

Crispness/Crunchiness is a texture property characterised by a material’s tendency to fracture suddenly under an applied force, often producing a characteristic sound. This property is commonly associated with snacks (e.g., potato chips), breakfast cereals, fresh fruits and vegetables, and baked goods (e.g., biscuits, crackers). Whilst crispness and crunchiness are closely related, they refer to slightly different sensory and mechanical characteristics.

Crispness is typically measured using a Texture Analyser to test a thin material during break strength testing, which identifies often a single sharp break/peak or a number of fracture events (peaks) on a force curve. Crunchy foods, like carrots, nuts, or apples, tend to resist deformation initially and require more effort/force to break down completely as the material tends to be thicker or more substantial.

Crispness/Crunchiness are also commonly tested when the sample is presented in bulk (usually due to the lack of sample uniformity from piece to piece). A crisp product tends to produce many small fracture peaks, while a crunchier product shows larger, more distinct peaks with a greater drop from peak to trough.

Crispness and crunchiness testing using a Texture Analyser is crucial in the food industry to evaluate the texture of various products. Here are key examples:

• Potato chip crispness: Evaluating the crispness of potato chips by measuring the forces and distance required to fracture them as a product that is no longer crisp may appear stale.
• Biscuit, cookie or snack bar crunchiness: Assessing the crunchiness of biscuits and cookies by measuring the force required to bite through them.
• Fresh produce (carrots, apples) assessment: Crunchiness is a desired trait in fresh fruits and vegetables, indicating freshness and firmness. Measuring crunchiness can help determine the optimal harvest time for fruits and vegetables to ensure the desired textural qualities.
• Fried food coating crispiness: Evaluating the crispness of fried food coatings by measuring the force required to cut/bite through a product such as chicken tenders or tempura.
• Snack food texture testing: Testing the crispness or crunchiness of snacks such as pretzels, popcorn, and corn chips by measuring the force needed to compress or break snack products in bulk.
• Breakfast cereal texture evaluation: Assessing the crispness of breakfast cereals (with/without milk), such as flakes and puffed varieties by crushing a controlled portion. Crunchiness is essential for cereals and granola to provide the expected texture when chewed. Manufacturers use texture analysis to maintain the right balance between crunchiness and hardness, ensuring the product doesn’t become too difficult to eat.
• Nut and seed snack crunchiness: Testing the crunchiness of nut and seed snacks, like almonds or sunflower seeds by measuring the force needed to crush/cut a nut or seed to assess its texture.
• Pizza crust crunchiness: Assessing the crunchiness of pizza crusts, from thin to deep-dish varieties by measuring the force applied when biting into a slice of pizza.
• Bread crust crispness: Testing the crispness of bread crusts, such as those on baguettes or artisan bread by measuring the force required to break/cut the crust of a loaf of bread.

In these examples, a Texture Analyser simulates biting or breaking actions by applying controlled forces to food samples. The resulting force-displacement data quantifies crispness or crunchiness, allowing manufacturers to maintain product quality and optimise formulations.

In a typical crispness/crunchiness measurement test, a probe/attachment can push down on a single sample (for homogeneous samples) or certain weight/number of pieces (in the case of irregular pieces) to cause failure.

Single pieces of homogenous product

Crisp Fracture Support Rig

Three Point Bend Rig

Craft Knife Adapter and Blades

Cylinder Probes

Multi-particulate or non-uniform products

Ottawa Cell

Kramer Shear Cell

Note: The testing of brittle materials will produce graphs that will not be variable in shape.  Failure of a sample does not occur in exactly the same way for each brittle sample and the graphs will display this inherent variability/irregularity.  However, there are ways that curves can be analysed that look for key events within the graph that can be repeatably obtained. From the graph you can observe/obtain the following:

• Rupture point
• Crispness
• Fracturability
• Crunchiness
• Brittleness
• Fracture strength
• Fracture distance
• Work of failure
• Breaking strength

Single piece of homogenous product

When measuring crispness/crunchiness of a single piece of sample, the force vs distance/time graph typically shows a sharp, sudden peak in the graph followed by a quick drop corresponding to brittle fracture – the material breaks quickly once a certain force threshold is reached. This indicates that the material fractures quickly with minimal force buildup and there is sudden fracture/failure of the sample. In very crisp foods (like crackers), there might be several peaks in quick succession as the material fractures in different spots or further smaller peaks might be shown until final breakdown or continued testing of the failed/broken sample fragments ends.

Multi-particulate or non-uniform products

When measuring crispness/crunchiness of a bulk sample, the force vs distance/time graph typically shows multiple sharp, narrow peaks during the distance travelled by the probe. Each peak corresponds to a fracture or break within the bulk material.

Crispness displays multiple small peaks whereas crunchiness often involves lower frequency and higher amplitude peaks. 

A full explanation of this curve and its analysis can be accessed within Exponent Connect software. Existing Exponent users can upgrade to Exponent Connect specification.

Below is a video example of how we can help you understand curve analysis for an example property. 

• Temperature: The temperature of the sample can influence its mechanical properties, affecting the measured crispness and crunchiness.
• Humidity: Ambient humidity levels can alter the moisture content of samples, potentially changing their crisp or crunchy texture.
• Test speed: The rate at which force is applied during the test can influence the measured results, as crisp and crunchy foods may respond differently to varying speeds of deformation.
• Compression distance: The extent to which the sample is compressed affects the force-displacement curve and resulting texture analysis.
• Storage conditions: How the sample is stored prior to testing can affect its moisture content and texture.

The Stable Micro Systems Texture Analyser is the ideal tool for optimising the measurement of crispness and crunchiness, offering versatile testing capabilities. It precisely quantifies key fracture attributes that occur quickly producing fluctuating curves with multiple peaks and troughs while incorporating Acoustic Envelope Detection to capture sound and video during testing for a multi-dimensional analysis.

With specialised testing attachments, it adapts to specific sample requirements across a wide range of single or multiparticle products, from snacks and cereals to fresh produce and baked goods.

Exponent Connect software provides enhanced accuracy by capturing data at 2000 points per second, providing highly detailed graphs for in-depth analysis. In contrast, lower data collection rates, often found in alternative equipment, can result in compromised accuracy and missed information, impacting the reliability of the results.

Advanced data analysis of fluctuating (jagged) force-distance-time curves and its ability to simulate consumer evaluation techniques ensure realistic, relevant results. Backed by Stable Micro Systems’ expertise in method development, it provides unparalleled accuracy for refining textures and maintaining quality standards in crispy and crunchy foods.