The apparent end point of primary drying was determined by comparative pressure measurement (i.e., Pirani vs. Experiments were conducted with 5% mannitol and 5% sucrose as model systems.
Thus, from product quality as well as process economics standpoint, it is very critical to detect the end of primary drying.
However, increasing the shelf temperature into secondary drying before all of the ice is removed from the product will likely cause collapse or eutectic melt. Freeze-drying is a relatively expensive process requiring long processing time, and hence one of the key objectives during freeze-drying process development is to minimize the primary drying time, which is the longest of the three steps in freeze-drying.
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