maximum storage times shown in Figure
33 for foods in the home freezer are probably conservative.
are carefully controlled at -18°C and the food was initially of high
quality then longer storage times can be achieved. However, most home
freezers are used for freezing as well as storage. This results in
temperatures rising above -18°C, which decreases optimum storage life.
Some deterioration in quality may have already taken place before
the food is frozen; for instance it may have been left in a hot car
while shopping. At -180°C loss in quality is very much slowed but
not completely stopped.
These slow changes,
which limit the storage life, do not have a marked effect on nutrient
content but eventually cause a noticeable change in eating quality.
Frozen foods do not become unsafe to eat even if kept for many years
at -180°C (see here
for safe handling of frozen foods).
To remain aware
of storage time, each package should be marked with the date as it
is placed in the freezer.