Freeze thaw indicator

An indicating device for evidencing thawing temperatures in a food storage compartment of a freezer having a container having an upper transparent portion and a lower opaque portion provided with inward projections. Colored water can be frozen in place within the opaque portion of the container and the container then set on it side in the freezer compartment. The projections hold the ice in place in the opaque portion of the container so that the extent of thawing is evidenced by the presence of water in the transparent portion of the container in the event of a rise in temperature in the freezer compartment.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to devices for indicating when a package of frozen 
food stored in a freezing chest may have thawed for a sufficient period of 
time for the food to deteriorate. 
2. Prior Art 
The process of quick freezing as applied to food and other products enables 
the food, when maintained in a frozen condition, to be preserved in its 
original fresh condition for an indefinite period of time. Frozen food, if 
thawed, can be re-frozen and maintained in a palatable and non-dangerous 
condition provided that it has not remained in its thawed condition for an 
extended period of time. 
It is considered that to re-freeze food that has been thawed out is a 
dangerous practise since bacteria can propagate at a prodigious rate 
unless maintained in a frozen condition. 
In some instances, freezer chests have been fitted with recording 
thermometers, however, this only indicates that maximum temperature has 
been reached, but gives no indication whether the food has reached a 
condition of complete thaw before power was re-established to re-freeze 
the food. Even if the duration of power failure is known, it will not 
establish whether the contents of the freezing compartment have thawed 
out, due to variences in the insulative characteristics of the equipment. 
Some thaw indicators have been developed which indicate whether thawing has 
taken place but they do not distinguish whether thawing was superficial or 
complete. They, therefore, do not indicate any quantitative measure of 
whether the food merely started to thaw or did, in fact, thaw out 
completely. Therefore, it can not be known whether the food has been 
subjected to the dangerous condition of being completely thawed and then 
re-frozen. 
These devices depend on the expansion of the ice to break a frangible 
partition, so that, if the temperature of the freezer rises above the 
melting point of the liquid, even for a short period of time, liquid from 
one compartment flows into the other compartment where it reacts with 
indicators to cause a calour change which is irreversible. 
There are several major objections to devices of this type. They are very 
difficult and expensive to manufacture. Being of a fragile nature, they 
can be accidentally broken to give false readings. Once frozen, they can 
not be thawed and re-used. Consequently, they must be discarded whenever 
it becomes necessary to de-frost the refrigerator or if they have been 
activated on one occasion. They do not give any quantitative indication as 
to whether a superficial thawing or a complete thaw has taken place. Many 
indicators do not provide permanent color retention and many show little 
or no color if maintained in a frozen condition for long periods of time. 
Examples of such failures are evident in the use of phenolphthalein or 
methyl orange. 
SUMMARY OF THE INVENTION 
The present invention provides a thaw indicator which can be re-used after 
thawing. 
The thaw indicator of the present invention, does not have multiple 
compartments or chemicals, and being without fragile seals or clamps is 
inexpensive to manufacture. The absence of these fragile seals and 
possibility of clamp failure provides freedom from leakage and subsequent 
false indication of thawing. 
The present invention provides a means of quantitatively determining 
whether a superficial thaw has occured or whether a period of complete 
thaw has taken place. 
The thaw indicator of the present invention includes a tube formed of a 
flexible material which is sealed at both ends, substantially half the 
length of the tube being rendered opaque, and the other half being 
transparent and a coloured liquid which has substantially the same 
freezing and melting points as water in the tube and in an amount 
sufficient so that when the tube is suspended in a position in which the 
opaque portion is lowermost the liquid is contained entirely within the 
opaque portion of the tube. 
Detailed description following, related to drawings, gives exemplification 
of apparatus according to the invention which, however, is capable of 
expression in means other than those particularly described and 
illustrated.

DETAILED DESCRIPTION 
Referring to the drawings, the indicator of the invention includes a 
tubular casing 10 which is closed at one end 11 and has a closure cap 12 
at the opposite end made of a transparent thermoplastic material, 
sufficiently stiff so that it can stand in an upright position, FIG. 1. 
The lower half 14 of the casing, is rendered opaque as by colouring or 
frosting or by application of decals or labels thereto, the other half 15 
of the casing being untreated so that contents of the casing are visible 
only through the upper half. The opague half is provided with inward 
projections 17 at intervals along its length. 
The casing contains a volume of water 19 which is coloured, the volume of 
water being sufficient so that when the casing is upright, i.e. with the 
transparent portion 15 upwards, the water is contained entirely within the 
opaque portion 14. Colouring used to colour the water can be any suitable 
type of dye or food colouring which is harmless when ingested. A suitable 
colouring is phenol red adjusted to its red colour range by any convenient 
harmless dilute alkaline, such as sodium, ammonium, potassium, phosphate, 
carbonate or hydroxide. 
In use the device is placed in a freezer compartment in the upright 
position, FIG. 1, and the coloured water frozen within the opaque portion, 
and is then laid on its side. FIG. 2, in the freezer compartment where it 
is clearly visible. The frozen mass of ice will not side into the clear or 
transparent portion due to the obstruction provided by the projections 17, 
however, in the event that temperatures within the freezer compartment 
rise sufficiently to thaw the water, the water will run into the 
transparent portion of the casing and thus afford evidence of the 
temperature change. Duration of time of exposure to thawing condition can 
be judged by the volume of water which may have been frozen in the 
transparent portion of the casing. Indicator marks, severally 21, on the 
sides of the transparent portion of the casing can be used to gauge the 
extent of thawing conditions. 
To reset the indicator for re-use, it is only necessary to thaw the water 
and re-place the indicator in a freezer compartment in the upright 
position as above described. 
It will be understood that although flexible materials such as 
thermoplastic are the most suitable materials from which the casing can be 
made in view of expansion of water to ice, the use of glass bottles and 
the like suitably shaped to accommodate expansion of water to ice, would 
be acceptable.