Thermal measuring and testing – Temperature measurement – Composite temperature-related paramenter
Patent
1981-03-12
1984-02-21
Myracle, Jerry W.
Thermal measuring and testing
Temperature measurement
Composite temperature-related paramenter
116206, 116216, 426 88, G01K 304, G01K 1116
Patent
active
044326564
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of monitoring the history of temperature versus time of a deep-frozen product in the way of a time integral of its temperature development, with an indicator for sensing the course of diffusion of water in a path of diffusion; and relates to an indicator for carrying out said method and to the utilization of said method.
STATE OF THE ART
There has been a need for a long time to monitor deep-frozen foodstuffs. Reference is made in this respect to U.S. patent specification Ser. No. 1,535,536 dating back to the year 1925, which relates to the monitoring of the storage temperature of ice cream. This published document was followed by a number of others relating to overcoming as to how the uncertainty with respect to the storage temperature of deep-frozen products with the help of a simple and inexpensive indicator. Attention is called in this regard to the publication by H. M. Schon and C. H. Byrne in "FOOD TECHNOLOGY", October 1972, in which relevant publications are listed in a summarized form. Most conventional indicators are based on the principle comprising the monitoring of a limit temperature on the deep-frozen products by indicating any, even though only brief exceeding of said limit temperature either immediately or with some delay within the order of magnitude of hours. Such indicators are known as "defrost indicators". Said indicators function in most cases on the principle that a liquid, which is in the frozen state at the required storage temperature, melts if the limit temperature is exceeded above -18.degree. C., and the liquid is absorbed by a wick or strip of paper, and subsequently flows to an indicating field where it causes a color change. Reference is made in this connection, for example to French patent specification No. 1,548,424, or U.S. Pat. No. 2,951,764.
However, the durability of deep-frozen products has been investigated more recently in greater detail. It was found that specific critical temperatures do not exist, but that the permissible storage time of deep-frozen products is rather reduced continuously as the temperature increases, namely with a quality reduction that takes place approximately logarithmically. It has become a customary procedure to show graphically by means of so-called durability curves the periods after which an acceptable quality limit can be still achieved as a function of the temperature. FIG. 1 shows a number of durability curves for various types of product, which are borrowed from the publication "Recommandations pour la preparation et la distribution des aliments congoles", 2nd edition, 1972, pages 118/119, published by the "Institut International du Froid", Paris.
Said durability curves vary for different product categories, and both the maximum permissible storage duration at -20.degree. C. and the storability as a function of the temperature may be different. Normally, the frequency of the temperature fluctuations plays a negligible role, with the exception of ice cream. More recently, it has become customary to use for the durability of deep-frozen products as a function of the temperature the so-called Q.sub.10 -value. This is the quotient which is obtained by dividing the duration of durability of a specific product at a defined temperature by the duration of durability of said product at a temperature that is 10.degree. C. higher. However, since said Q.sub.10 -value depends on the temperature, which means, for example, that its value in the range of -2.5.degree. C. and -12.5.degree. C. is different from the one in the range of -10.degree. C. and -20.degree. C., the Q.sub.-20.degree./-2.5.degree. C.-value is introduced in the present case instead of the Q.sub.10 -value for the characterization of the function of the temperature, the former covering the storage temperature range of -20.degree. C. and -2.5.degree. C. that is of interest to deep-frozen products just prior to thawing.
According to a rough classification the Q.sub.-20.degree./-2.5.degree. C.-values are as follow
REFERENCES:
patent: 2552477 (1951-05-01), Cole
patent: 2762711 (1956-09-01), Zopf
patent: 3615719 (1971-10-01), Keller et al.
patent: 3620677 (1971-11-01), Morison
patent: 3695903 (1972-10-01), Hahn et al.
patent: 3946611 (1976-03-01), Larsson
patent: 4137049 (1979-01-01), Couch et al.
patent: 4154107 (1979-05-01), Grozen et al.
Myracle Jerry W.
Noland Tom
Rosen Lawrence
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