A eutectic plate stores cold as the heat given off when its liquid freezes, and takes it back as it melts. A plate that is not fully frozen therefore still gives cold at its melting point, but for a shorter time: for example, if a fifth of the mass is still liquid, roughly a fifth of the cold reserve is missing. A hard, icy outer surface does not show that the core is frozen.
Why it freezes incompletely. GEBHARDT asks for plates to be frozen at least 5 °C below their melting point; for item 6081958, with a melting point of -18 °C, the table gives a freezing temperature of -23 °C and 24 hours (8 to 24 hours depending on the cooling technique). Setting the freezer to the plate's own melting point, -18 °C, does not freeze it fully, and the 24 hours in the table is freezing time, not holding time on the road. Without an air gap between plates the cold air cannot circulate, which is why GEBHARDT offers freezing racks. For the rack layout see how to freeze eutectic plates, and for the model and freezing values the GEBHARDT eutectic plate document.
What to do with a doubtful plate
If the plate has not shipped, set it aside and check the batch number, rack position and freezer load. If incomplete freezing repeats on the same rack or batch, do not blame the plate; look at airflow and loading density, because preparation verified with a few plates does not give the same result on a large warm batch packed tightly onto one rack. If the plate has already left, review product temperature, the logger record and the batch data with the quality manager; the appearance of the plate does not decide it.
