In addition to the formulation and raw material issues described above, there are processing issues that can affect product stability. For example, stability testing is typically required the first time a new formulation is made on a large scale. This is because the way in which the product is made on a large scale can have a dramatic effect on its stability. This is particularly true of emulsions, because the energy used in processing determines particle size and distribution, which helps determine product stability. The only way to fully assess the impact of the chosen manufacturing method on product stability is to evaluate samples made under actual production conditions. This may require that a trial production batch be made prior to commercialization of the formula. At the very least, stability testing should be done on the first production batch of any new product, so that the impact of actual production processing conditions may be evaluated.
Once a manufacturing process has been shown to be successful, any changes to that process may require additional testing. Alterations in the order of raw material addition may be necessary to reduce processing time; changes in heating and cooling rates may occur due to differences in heat transfer in large batches; and different mixing conditions will all affect the amount of shear the product experiences. Any one of these changes will cause stability problems.
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