Evaluation of hardness of a premium brand and budget brand potato chips by bulk compression using an Ottawa Cell.
The quality of a product and its appearance are important factors to a consumer when it comes to product selection. Quality and appearance can be described by colour, flavour and taste, in addition to physical attributes such as size, shape and texture.
Using the CT3 Texture Analyser, the textural qualities of crisps can be assessed. Weighed samples are placed into an Ottawa cell and compressed by a plunger at a given speed. Hardness is determined by the maximum force on the graph. This correlates with the force required to crush the chips between the molars. The area under the graph is a measurement of work done and correlates to the energy required to overcome the strength of the internal bonds within the chips by the molars. The quantity of fractures can also be measured which gives an indication of the crispiness/crunchiness of the sample. The fracturability values are the initial fractures and give an indication of the samples brittleness. By quantifying these textural attributes, the quality of crisps can be assessed to meet customer satisfaction.
Weigh out equal portions of chips ready for testing. The weighed amount of sample should fill the Ottawa cell between 50 – 75 % of its fill capacity.
Note: When testing different sample types, the hardest sample is best tested first in order to anticipate the maximum testing range required. This will ensure that the force capacity covers the range for other future samples.
For comparison purposes, the weight of the samples to be tested should be the same from test to test.
As the samples are of variable geometry, the results are an average of the forces required to crush the sample.
Figure 1 shows the compression test for 10 g of budget and premium brand chips using the Ottawa cell. The maximum force value is a measure of sample firmness/hardness (force required to compress and crush the sample between the molars). The area under the curve from the start of the test to the maximum force value is a measure of work done (energy required to break the strength of the internal bonds within the sample). The fluctuations in force values on the graph are the result of multiple fractures generated during the compression. Tests have been performed at room temperature
Figure 2 shows the force vs. distance, distance graph for the compression of 10 g of two brands of chips using an Ottawa cell. Tests have been performed at room temperature. The maximum force value is a measure of sample hardness. This is the amount of force required to compress and crush the sample between the molars. The area under the graph from the start of the test to the target distance point (30 mm) is a measure of work done. This is the energy required to break the strength of the internal bonds within the sample. Once the target distance has been attained, the plunger withdraws from the sample, as seen by the sudden drop in force to zero load. The horizontal line shows the distance the plunger travels in returning to its starting position above the sample surface. (The negative distance values indicate a travel distance of more than 5 mm before the probe makes contact with the chips in the cell.)
When a trigger force of 30 g has been attained at the sample surface, the plunger proceeds to compress the sample at a speed of 2 mm/s over a distance of 30 mm. During this time, the sample is fractured multiple times as seen by the fluctuations on the graph. The maximum peak value is a measure of sample hardness. The area under the graph from the start of the test to the maximum force value is a measure of work done. Once the plunger has reached the target distance (30 mm), the probe withdraws from the sample and returns to its starting position at the sample surface.
The table below is a summary of the results.
The budget chips are twice as hard as the premium chips as seen by their hardness values and require a higher distance of compression before fracture as seen by the 1st fracture deformation distance values, indicating a higher elastic component. The budget chips are also less brittle in comparison to the premium chips with a lower fracturability value. The quantity of fractures for the premium chips are twice those for the budget chips, indicating that the premium chips have a crunchier and crispier texture compared to the budget brand.