Cryogenic labels to detect an exposure to sub zero temperatures for a predetermined period of time

摘要

A coloured label changes colour when exposed to sub-zero temperatures for a predetermined period. Different initial colours indicate different periods. The colour of the label is chosen to indicate the life of a frozen food product and a change of colour indicates that it has reached the end of its life. Examples include yellow, red and green labels changing to black after 1, 2 and 3 months at sub zero temperatures respectively.