Determining gel strength, which is also referred to as bloom, is a common practice for many food producers. Gel strength is an important measurement because it has a strong influence on mouth feel. In a typical gel strength test, the amount of force needed to rupture the specimen and the extension at rupture are reported.
A manufacturer of gummy candies was interested in purchasing equipment that would allow them to determine the gel strength of their products on their own, as opposed to hiring an outside test lab. Gel strength is dependent on test speed, geometry, and size of the puncture probe, as well as the alignment of the probe. A misaligned probe could result in a stress concentration at the corner of the probe. Unnecessary stress concentrations may cause a premature failure. It is important to ensure that proper equipment is used. We recommend the use of a 3-jaw chuck to fix the probe in place. With a 3-jaw chuck, the alignment will always be optimum, since the device is self-centering and there is no subjective manual alignment necessary. The diameter of the probe is dependent on the specimen geometry or standard being followed. In the case of gummy candies tested at Instron, a 5/16-inch probe was used and a test speed of 2 in/min.
We suggest using either our 3300 or 5500 electromechanical testing systems equipped with a 3-jaw chuck and food probe set for determining the gel strength of a variety of materials. Bluehill® 2 software is an appropriate software package - the automatic preload feature will allow a system to automatically determine the starting point so that consistent extension at rupture values can be achieved. It is important to make sure that a proper load cell is used. Because the gel strength for some specimens may be very low, you should select a load cell for the respective testing system that will allow you to maintain optimum accuracy at the point of specimen rupture.