Our lab team tests gram strength on all gelatin and animal glues we receive into our manufacturing facility. We then use that number in correlation to the viscosity to determine what raw materials get used in our cake glues and dehydrated hide glue.
The gram strength of a material is important in our industry because it correlates to the rigidity of the glue after the bond has been formed. The higher the gram strength, the stronger the cohesive forces in the glue. Cohesive forces are the attractive forces between the molecules in the glue, so as the gram strength gets higher, the glue will stick to itself better. The bond will also become more rigid as the gram strength increases.
Gram strength is also referred to as "jelly" or "bloom" strength.
The difference between jelly and bloom strength is the concentration of the solution. The jelly strength is measured from a 12.50% solution of the gelatin after it has formed a gel. Bloom strength is performed using a 6.67% gelatin solution.
For testing, the solution of gelatin is prepared under specific experimental conditions. Gel rigidity arises from molecular interactions within the glue.
Interactions include, but are not limited to, secondary interactions and molecular entanglement. Protein (gelatin) molecular chains form non-covalent bonds to themselves. This interaction increases jelly strength. Molecular entanglement, based on the length of the chains interact, which increases the rigidity of the glue.
As you can see, a lot goes into make sure the raw materials going into your glue are top notch. Gram strength testing plays a major part in providing top quality glue products.