Bean hardness measurement

PRINCIPLE OF THE TEST

Evaluation of the hardness of dry cooked beans by bulk compression.

CONTEXT

Compression testing is a commonly used method to measure the force required to cause sample failure. The maximum force characterizes the hardness of the sample. The area under the curve for the applied force versus the strain of the sample is a measure of the energy required to crush the sample.

METHOD

Equipment : CT3 with 50 kg load cell

Luminaire base table (TA-BT-KIT)

Ottawa cell (TA-OC)

Extrusion plate

Capture drawer

TexturePro CT software

Settings :

Type of test: Compression

Pre-test speed: 2.0 mm / s

Test speed: 2.0 mm / s

Post-test speed: Select return to test speed

Target type: Distance

Target value: 10 mm

Trigger force: 50 grams

SAMPLE PREPARATION

Remove the beans from their storage bags just before testing. Weigh 30 g of beans and pour the sample into the Ottawa cell (this amount will be enough to fill about 50 % of the Ottawa cell).

PROCEDURE

Attach the plunger to the instrument.

Place the fixture base table on the instrument base and lightly tighten the thumbscrews to allow some degree of mobility.

Insert an empty Ottawa cell on the base table and tighten in position using the side screws.

Align the plunger with the Ottawa cell by lowering the plunger and readjusting the position of the Ottawa cell so that the plunger can be lowered into the cell without touching the edges of the cell.

When alignment is complete, tighten the base table thumbscrews to prevent further movement.

Place a collection drawer under the Ottawa cell to collect any extruded sample.

Lift the plunger to allow easy removal of the cell.

Place the weighed sample in the Ottawa cell and spread it out to create a flat surface.

Return the cell containing the sample to the base table, remembering to tighten the side screws.

Lower the plunger a few millimeters above the sample surface. Note: For comparison purposes, the start distance above the sample surface should remain the same for all samples tested.

The plunger was lowered to 50mm from its starting position so that it was only a few millimeters above the sample surface. The starting position chosen should be such that the plunger does not come into contact with the surface of the sample before testing.

Start the test. When proceeding to the next test, clean the plunger, extrusion plate, and Ottawa cell to remove all traces of a previous sample.

Note: When optimizing test parameters, the harder sample is tested first in order to predict the maximum test range for subsequent samples.

RESULTS

The following graphs show the hardness of dry cooked beans for different cooking time intervals.

Figure I shows the force as a function of time; the maximum value is the hardness of 30 g of beans cooked for 5 minutes and 7-10 minutes respectively. The tests were carried out at room temperature.

Figure II shows force as a function of distance; the maximum value is the hardness of 30 g of beans cooked for 5 minutes and 7-10 minutes respectively. As the plunger compresses the sample a distance of 10 mm, an increase in the load is observed. Once the specified distance is reached, the plunger withdraws from the sample, returning to its starting position as shown in the lower portion of the graph.

DISCUSSION

When a trigger load of 50g has been reached at the sample surface, the probe will compress the sample to a specified distance of 10mm. During this time, the force increases, as the sample begins to fracture.

The maximum force value obtained over the specified distance is a measure of hardness. The higher the maximum force value, the harder the sample. The area under the curve is a measure of the hardness work done; the larger the area under the curve, the harder the sample. From Figure 1, beans that are 7-10 minutes are harder and require more energy to compress than those cooked for 5 minutes.