WO2001051903A1

WO2001051903A1 - Internal temperature measuring device

Info

Publication number: WO2001051903A1
Application number: PCT/US2001/000890
Authority: WO
Inventors: Robert Burton; Robert Parker
Original assignee: Burton Plastics
Priority date: 2000-01-11
Filing date: 2001-01-11
Publication date: 2001-07-19
Also published as: WO2001051903A8

Abstract

An inexpensive device for measuring the temperature distribution in meat, poultry, fish is disclosed. It is easy to read, fast and convenient and low in cost without the use of batteries. It is also reusable. While the use of reversible materials is described, the possible use of multiple irreversible materials in the thickness of the meat is also possible.

Description

Title: INTERNAL TEMPERATURE MEASURING DEVICE

FIELD OF THE INVENTION

The present invention relates to a device for determining the temperature distribution of a substrate such as meat, poultry or fish during cooking.

BACKGROUND OF THE INVENTION

Barbecuing meat, poultry or fish on an open fire can present the chef with many cooking variables in order to determine when the food is done. The heat may not be uniform, the thickness of the meat can be variable, and the standard doneπess measurement such as "rare", "medium" or "well done" can be quite subjective. Also, the relative thickness of the item being cooked can influence the amount of time necessary for proper preparation. For instance, cooking time might vary dramatically for a thin hamburger versus a thick steak. Similar variables occur with ovens and stoves due to temperature fluctuations of the heat source.

One may make cuts in the meat to visually observe the interior doneπess during the cooking process, but this is quite subjective, and may allow internal juices to be lost. There are a number of products on the market that use irreversible thermochromic materials which will show if the food has exceeded some cntical temperature related to the doπeπess and/or safety of the food "(Above some critical temperature that can kill Bacteria.)"

A product called "T.Stick", which is embodied by United States Patent No. 5,622,137 and sold by M. E. Heuck Co., uses an irreversible thermochromic material to show if meat, poultry, or pork has exceeded a given temperature.

Another product using irreversible indicators was patented by Hans O. Ribi, where their irreversible indicators are coated onto a plastic probe in United States Patents Nos. 5,685,641 and 5,918,981. Another product designed to aid in cooking is the Tempfork, developed by Mr.

Richard Murtagh. Here a thermocouple or similar sensor is used in the tines of a fork to probe the food and sense the temperature. This expensive battery-operated device is reusable, but only gives a temperature measurement at the localized point of insertion. Since the temperature measurement is localized, it can be inaccurate. All these products have a common design fault. They all only indicate the temperature or peak temperature at a particular place or thickness in the food. This can be quite misleading and give erroneous results. A need exists for a device that accurately determines the internal temperature of food during cooking.

SUMMARY OF THE INVENTION

The present invention relates to a device that accurately determines the internal temperature of meat, poultry or fish during cooking.

The present invention further relates to a device using thermochromic materials to determine a temperature gradient across a thick plane such as that encountered with a piece of meat, poultry or fish during cooking.

DRAWINGS Figure 1 illustrates the temperature distribution of an infinite thick plane when exposed to an instantaneous temperature or constant heat flux;

Figure 2 illustrates a planar view of an embodiment of the present invention;

Figure 3 illustrates a cross-sectional view of the invention of Figure 1 taken about line A-A'; Figure 4 illustrates an exploded side view of the invention of Figure 2;

Figure 5 illustrates a cut-away view of an embodiment of the present invention;

Figure 6 illustrates another embodiment of the present invention;

Figure 7 illustrates a cross-sectional view of the embodiment of Figure 6; and

Figure 8 illustrates a cross-sectional view of the discontinuous metal embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides a device which can be inserted into or placed in contact with a thick substrate for determining the temperature gradient across the thick substrate. This provides a more accurate temperature than the local reading obtained by simply inserting a thermometer into a substrate. In one embodiment, the present invention determines temperature of the food during cooking, but does not take a single, isolated reading of the temperature at the point in which it is inserted in the food, instead determines temperature distribution across a plane of the food resulting in a more accurate measurement.

The temperature distribution of an infinitely thick plane when exposed to an instantaneous temperature or constant heat flux is illustrated in Figure 1. As can be seen, this results in a large temperature gradient which will flatten with time into a linear gradient.

The present invention determines the temperature gradient and displays this temperature information to the user through the use of thermochromic stripes. As best seen in Fig. 2, the present invention uses one or more reversible thermochromic stripes that are oriented in a general normal position to the thickness of the substrate such as meat, poultry or fish.

The temperature of a substrate can vary from point to point within the substrate depending thickness and a variety of other factors. As illustrated in Figure 3, the present invention determines the temperature for the substrate, not just the particular localized point of contact between the substrate and the invention. The temperature distribution in an infinite thick plane when exposed to a temperature instantaneously or a constant heat flux can be mathematically described by the following.

Where time

It results in a large temperature gradient that will flatten with time to a linear gradient as seen in Figure 1.

As best seen in Figures 2 and 4, an embodiment of the present invention is illustrated. The polymer thermochromic is mounted on an embossed or flat thin .005" - .020" metal carrier. A thermochromic material, as used herein, is any material that changes color based on a change in temperature. In an embodiment of the present invention, the end of the carrier may be in contact with the grill or plate, but the heat sensitive reversible thermochromic material is some distance away from the flames (1/16" - 3/16") so that the surrounding meat will prevent the temperatures that may deg rade the thermochromic materials.

A number of thermochromic materials can be used for the present invention, such as Matusui's reversible thermochromic materials, macro encapsulated Mercury Chloride, or high temperature memory liquid crystal materials supplied by David Liquid Crystals, as well as reversible Poly Di Acetylene materials. In the example shown in Figure 4, a (.009") stainless steel carrier is shown that has been embossed so that the adhesively bonded thermochromic will not peel off the stainless steel.

It would also be possible to print, paint or emboss the thermochromic directly on the metal carrier using bright passive colors under the thermochromic. The thermochromic material may be embossed in the metal to stiffen particularly thin metal carriers while aiso preventing the thermochromic material from peeling off the carrier.

While stainless steel has many thermal advantages that will be discussed later and is the preferred metal, other metals (Iron, Titanium, etc.) may be used.

The construction or assembly stack is shown in Fig. 3. It is composed of stainless steel, a high temperature pressure adhesive with a decal showing passive colors, then thermochromics, all printed on a transparent polymer such as

Polycarbonate from G.E. (.003" - .007") or polyester from Dupont (.001" - .007") or polyamide.

After some period of time when the meat has been on the grill (depending on the thickness and heat), the chef will insert the indicator in the meat. Heat will diffuse into the device from two sides, rapidly heating the stainless steel and the thermochromic material. This will be for about five seconds depending on the thickness of the polymer and the stainless steel.

The unit will not reach equilibrium but will be from 5% to 10% of the equilibrium temperatures as shown in Fig. 1. The meat will be at a greater temperature than the temperature required to change the thermochromic material completely. For example, a Matsui material which has a specified turn-on temperature of 47°C would turn from black to clear when the meat is at 52-53^DC, hence allowing the use of lower temperature thermochromic materials.

This would mean the first strip in Fig 2 would go from black to yellow, for example, showing the meat is rare. If the center of the meat is cool only the sides of the meat that have heated would show yellow. This in effect would show the temperature distribution in the meat. The stripe of yellow is not entirely covered with the thermochromic material so the chef or user can compare the cleared thermochromic with the base color. The second stripe may be 50"C and the meat would have to exceed 55-56°C to transform the color. Again, if the center is cooler, this stripe may not change entirely- One of skill will appreciate that the thermochromic material may be mounted on a thin stainless steel carrier or other similar poor metal conductor. This is done to generate a rapid response once the invention is in contact with the substrate whose temperature is being measured. As illustrated in Figure 5, this embodiment may also be curved and have a pointed tip to facilitate insertion or piercing of meat, poultry or fish.

In another embodiment of the present invention, as illustrated in Figures 6 and 7, the thermochromic material may be mounted in a frame for thermal isolation. The frame may be of any suitable material such as metal or plastic. Such an embodiment can be utilized for immersion into vats of liquids, amongst other things.

In addition to fast response time and little or no transverse cooling, one may increase the viewing time by incorporating discreet masses or discontinuous metal in contact with the polymer film. Figure 8. While most of the applications are concerned with barbecuing or cooking and preparation of food, this same concept may be used for many other applications such as determining the temperature inside of a carton of produce such as refrigerated chicken, lettuce, steaks, etc. Here the probe with the thermochromic materials are mounted on a sharp piercing metal carrier that can puncture the carton and reveal the temperature distribution through the carton. A similar device can be used to determine if recently cooked food has been cooled down under refrigeration to a safe temperature within a given amount of time so bacteria will not grow.

Other applications using this invention may be determining the temperature distribution in a hay bale so as to detect heat given off from a bacterial action which can cause spontaneous combustion. For farmers wanting to know if the soil is warm enough for seed germination, a metal spike with various thermochromic formulations on it may be pounded into the ground. This rugged device when retracted would show the soil temperature distribution.

Claims

1 . An internal temperature measuring device for determining the temperature of a substrate comprising: a metal carrier; and at least one stripe of thermochromic material mounted to said metal carrier in a generally normal position to the thickness of the substrate food.

2. The internal temperature measuring device of claim 1 wherein said metal earner is a poor metal conductor.

3. The internal temperature measuring device of claim 2 wherein said metal carrier is stainless steel.

4. The internal temperature measuring device of claim 3 wherein said stainless steel metal carrier further comprises a pointed tip to facilitate insertion into the cooking food.

5. The internal temperature measuring device of claim 1 wherein said at least two stripes of thermochromic material is embossed onto said metal carrier.

6. The internal temperature measuring device of claim 1 wherein said at least two stripes of thermochromic material are adhered to said metal carrier.

7. The internal temperature measuring device of claim 1 further comprising directional information stamped onto said metal carrier.

8. The internal temperature measuring device of claim 1 wherein said at least one thermochromic stripe is a passive color indicator.

9. An internal temperature measuring device for determining the temperature of a substrate comprising: a frame; and at least one stripe of thermochromic material disposed within said frame.

10. An internal temperature measuring device for determining the temperature of items in cold storage comprising: a metal carrier and at least two stripes of thermochromic material mounted to said metal carrier in a generally normal position to the thickness of cold storage item.