20 July 2026, 03:34 PM
Our laboratory encountered a persistent problem while conducting standard Bloom strength tests: operators continued to obtain inconsistent results when testing products from the same batch.
To determine the cause of these discrepancies, we investigated and troubleshot every step of the testing process. We found that human factors influenced both sample preparation and the testing environment, leading to inconsistent results. The following are the primary reasons we identified for the variations observed among different technicians:
Evaporation During Heating
One operator sealed the flask or covered it with a watch glass while heating the gelatin, while another left it completely or partially open. This resulted in differences in water evaporation, leading to variations in sample concentration. During testing, even a difference of just 0.3% can alter gel strength by several Bloom units.
Stirring Speed and Air Bubbles
One operator stirred the solution vigorously, while another stirred it gently. Vigorous stirring is likely to introduce air bubbles, resulting in lower test values.
Cooling Time
Gelatin itself is extremely sensitive to changes in temperature and time. If an operator allows the flask to cool on the lab bench for a longer period before immersing it in the water bath, this alters the formation of the crystal network.
Meniscus Alignment with the Probe
Some operators are not meticulous enough when leveling the gel surface or precisely aligning the probe with the center. An off-center or tilted surface can result in uneven force distribution.
Environmental Humidity During Testing
If one operator leaves the gel flask open on the lab bench in a dry room for 10 minutes before pressing the “Start” button, while another operator tests it immediately, the measured hardness values will differ. The first operator’s procedure allows a hard film to form on the gel surface.
Have you ever encountered this situation? How can operator bias be avoided? We welcome your feedback.
To determine the cause of these discrepancies, we investigated and troubleshot every step of the testing process. We found that human factors influenced both sample preparation and the testing environment, leading to inconsistent results. The following are the primary reasons we identified for the variations observed among different technicians:
Evaporation During Heating
One operator sealed the flask or covered it with a watch glass while heating the gelatin, while another left it completely or partially open. This resulted in differences in water evaporation, leading to variations in sample concentration. During testing, even a difference of just 0.3% can alter gel strength by several Bloom units.
Stirring Speed and Air Bubbles
One operator stirred the solution vigorously, while another stirred it gently. Vigorous stirring is likely to introduce air bubbles, resulting in lower test values.
Cooling Time
Gelatin itself is extremely sensitive to changes in temperature and time. If an operator allows the flask to cool on the lab bench for a longer period before immersing it in the water bath, this alters the formation of the crystal network.
Meniscus Alignment with the Probe
Some operators are not meticulous enough when leveling the gel surface or precisely aligning the probe with the center. An off-center or tilted surface can result in uneven force distribution.
Environmental Humidity During Testing
If one operator leaves the gel flask open on the lab bench in a dry room for 10 minutes before pressing the “Start” button, while another operator tests it immediately, the measured hardness values will differ. The first operator’s procedure allows a hard film to form on the gel surface.
Have you ever encountered this situation? How can operator bias be avoided? We welcome your feedback.