The grinding process also causes an increase in the overall product temperature, and at this point a stabilizer might be added, such as hydrogenated vegetable oils.
This oil then crystallizes once the product returns to ambient temperatures, and the formed crystalline lattices trap the stabilizer particles within the paste.
[5] At room temperature, the oils in natural peanut butter remain liquid, causing a phase separation.
[7] For accurate data, rheometers typically require no-slip, and the properties of peanut butter do not satisfy this condition.
Squeezing flow viscosimetery uses two parallel plates to compress a fluid uniaxially[7] This method can be used to better understand the viscoelastic properties of peanut butter.
Another way to overcome the wall-slip effects, is to rough up the contact surface of parallel plate rheometers using a material such as sandpaper.
[8] Both stabilized and unstabilized peanut butter displayed highly non-linear behavior,[8] and the storage (G’) and loss (G’’) modulus was determined.
[8] Mentioned previously, the increase in strain causes loosely aggregated peanut particles to break, allowing a more homogeneous oil-peanut mixture to form.
However, the increase in moduli at a critical strain implies a less homogenous structure is being formed, causing a greater resistance to flow.
[8] Meaning at a critical strain, the flow would cause particles to create a less ordered structure resulting in an increase in viscosity.
However, if the angular frequency was decreased and increased again, a different behavior emerged, and the peanut butter was unable to retain the same initial complex viscosity.
This is likely due to an increase in peanut oil produced by a higher grinding time, causing a lubricating effect to decrease viscosity.
[10] Increasing the grinding time also produced peanut butter with a narrower particle size distribution with high densities.