GB2244132A - Temperature-responsive food probe - Google Patents

Temperature-responsive food probe Download PDF

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Publication number
GB2244132A
GB2244132A GB9109181A GB9109181A GB2244132A GB 2244132 A GB2244132 A GB 2244132A GB 9109181 A GB9109181 A GB 9109181A GB 9109181 A GB9109181 A GB 9109181A GB 2244132 A GB2244132 A GB 2244132A
Authority
GB
United Kingdom
Prior art keywords
food
temperature
probe according
sensing means
elongate portion
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB9109181A
Other versions
GB9109181D0 (en
GB2244132B (en
Inventor
Colin David Rickson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Liquid Crystal Devices Ltd
Original Assignee
Liquid Crystal Devices Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Liquid Crystal Devices Ltd filed Critical Liquid Crystal Devices Ltd
Publication of GB9109181D0 publication Critical patent/GB9109181D0/en
Publication of GB2244132A publication Critical patent/GB2244132A/en
Application granted granted Critical
Publication of GB2244132B publication Critical patent/GB2244132B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
    • G01K1/02—Means for indicating or recording specially adapted for thermometers
    • G01K1/026—Means for indicating or recording specially adapted for thermometers arrangements for monitoring a plurality of temperatures, e.g. by multiplexing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/12—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance
    • G01K11/16—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance of organic materials
    • G01K11/165—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance of organic materials of organic liquid crystals
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6447—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors
    • H05B6/645—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors using temperature sensors
    • H05B6/6452—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors using temperature sensors the sensors being in contact with the heated product

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

A temperature-responsive food probe (1) comprises an elongate portion (2) insertable into food and having liquid crystal temperature sensing means (7), positioned along its length. The temperature sensing means is preferably responsive to temperatures in excess of 60 DEG C and is intended to provide a profile of the temperature within the food on withdrawal of the probe from the food. <IMAGE>

Description

TEMPERATURE-RESPONSIVE FOOD PROBE This invention relates to a temperature-responsive food probe for identifying regions of recently cooked or heated food which have not been heated to a desired minimum temperature, e.g. sufficient to kill bacteria or the like in the food. In particular, but not exclusively, the invention finds application in detecting insufficiently heated regions of food heated or cooked in a microwave oven.
Temperature-responsive food probes are already known.
One known type of food probe comprises a conventional bulb thermometer which is insertable into a recently microwaved food product to measure its internal temperature. Another known type of food probe has a thermocouple at one end which, also, is able to measure the internal temperature of a food product. However, both these known food probes, when inserted into food or a food product, are only able to sense the internal temperature of the food or food product in the region of the latter immediately surrounding the inserted temperature-sensing bulb or thermocouple, i.e.
only around the free end or tip of the inserted probe.
These known food probes are also relatively expensive.
Temperature probes employing liquid crystal temperature sensing means are known for other applications. For example US-A-4,445,788 discloses a soil probe for measuring soil temperature. This known soil probe is intended to indicate soil temperatures whilst still inserted in the soil, the display of discrete liquid crystal sensing means being transmitted above ground by means of light conductors. However this known soil probe is expensive to manufacture and is unsuitable for sensing high temperatures, e.g. in excess of 60"C. Another known temperature probe is disclosed in GB-1440292 employing different liquid crystal materials along the length of the probe for sensing different temperatures. These liquid crystal materials are not suitable for sensing wide temperature ranges and thus do not provide a temperature profile or map in use.
The present invention seeks to provide a food probe which overcomes the disadvantages outlined above associated with known food probes. In particular the present invention seeks to provide a food probe which is insertable into recently heated food to provide a temperature-responsive heat map or profile of the food throughout the depth of insertion of the probe to indicate any cool regions in the heated food.
According to the present invention a temperature-responsive food probe comprises an elongate portion insertable into food and provided with liquid crystal temperature sensing means along its length for sensing the temperature of heated food throughout the depth of insertion of the elongate portion into the food, the temperature sensing means providing a visual indication, at least for a short period of time immediately after withdrawal of the elongate portion from its food-inserted position in the heated food, of any temperature sensed regions of the heated food which are outside a predetermined temperature range having a minimum temperature in excess of 60"C.
In use a food probe according to the invention is intended to indicate the position of any temperature-sensed part of the heated food which is at a temperature outside a predetermined temperature range, for example from 60"C to 1200C, e.g. 70"C to 100"C, thereby indicating whether or not the food has been under- or over-heated. In particular, the liquid crystal material is intended to locate "cool" spots in the heated food, e.g. regions of the heated food whose temperature is below the minimum temperature of said predetermined temperature range The liquid crystal material may be of the type having a clearing point at this minimum temperature.Preferably, however, the liquid crystal material is thermochromic, preferably of the chiral nematic type, with the start of the color phase occurring when subjected to said minimum temperature on insertion of the elongate portion into the heated food. Preferably the "color phase temperature range" of the liquid crystal material (i.e. the temperature range over which the thermochromic liquid crystal material displays color) will be at least substantially the same as the said predetermined temperature range. However if the liquid crystal material is housed in a good thermally insulating housing, this does not necessarily follow. In such instances the color phase temperature range may extend over a lower range of temperatures than in said predetermined temperature range.The thermochromic liquid crystal material is conveniently applied to an opaque, e.g. black, backing layer, so that the temperature sensing means appears black at temperatures outside, i.e. above or below, the temperature range and colored at temperatures within the temperature range. The precise color of the liquid crystal material at any region along the length of the elongate portion will of course depend on the temperature to which it is heated by the heated food when the elongate portion of the probe is inserted into the heated food.
On withdrawal of the elongate portion from the heated food, the temperature of the liquid crystal material will fall towards the ambient air temperature. However the liquid crystal material is conveniently sufficiently thermally insulated for there to be a time delay to enable a "reading" of color before the temperature of the temperature sensing means falls too low. For example, the liquid crystal material may be surrounded by a thermally insulating material, e.g. plastics material such as polished polycarbonate material, at least part of which is light-transmitting to enable the temperature sensing means to be viewed.If the temperature sensing means comprises a black carrier strip having the liquid crystal material printed on one or each of its opposite sides, the printed strip may be positioned between two clear facing sheets, e.g. of polished polycarbonate material, permanently secured. e.g. welded, together. Alternatively it may be desirable to house the temperature sensing means carrying the liquid crystal material between a clear facing sheet and a heat conducting, e.g. metallic or metal based, sheet.
Preferably the elongate portion has a pointed end to facilitate insertion into the food. Conveniently the temperature sensing means extends substantially the entire length of the elongate portion.
An embodiment of the invention will now be described, by way of example only, with particular reference to the accompanying drawing, in which Figures 1 to 3 show in plan three parts, respec tively, of a food probe which, when assembled together, form a food probe according to the inven tion, Figure 4 is a sectional view, on an enlarged scale, taken on the line IV-IV of Figure 1, and Figure 5 is a modified sectional view similar to that shown in Figure 4 and showing a modified version of the food probe part shown in Figure 1.
Figures 1 to 4 show elements of a temperature-responsive food probe. In Figure 1 there is shown a clear molded first housing part 1 having a blade-like elongate portion 2 pointed at one end and a handle at its other end formed by a hilt-like finger grip 4 and a thumb press circular flange part 5. As can be seen in Figure 4, the elongate portion 2 has a shallow recess 6 extending along its length. Figure 2 shows an elongate thermochromic liquid crystal display strip 7, also having a pointed end, intended to be posi tioned in the shallow recess 6. Figure 3 shows a clear molded second housing part 8 intended also to fit in the recess 6 and to sandwich the display strip between the housing parts 1 and 8. The parts 1 and 8 should be permanently sealed together, e.g. by ultrasonic welding or bonding, to sealingly encapsulate the display strip 7 whilst enabling it to be viewed.Thus when the first and second housing parts 1 and 8 are so joined together, opposite sides of the display strip 7 can be viewed through the elongate portions of the two parts 1 and 8 between which the display strip is sealingly located.
At least one of the first and second parts 1 and 8 may be made of any suitable light-transmitting material which is able to withstand high temperatures, e.g. in excess of 100"C and preferably 1200C. A particularly suitable material is polished polycarbonate material which is also non-toxic, can be easily washed or cleaned and serves to thermally insulate the display strip 7 whilst providing a thermally conductive path sufficient to transmit heat to activate the liquid crystal material and give enough thermal inertia to enable a reading to be made on withdrawal of the probe from heated food.
The thermochromic liquid crystal display strip 7 comprises a black carrier strip having thermochromic liquid crystal material applied, e.g. printed, to its opposite sides. If a printing process is used, the printing "ink" suitably comprises microencapsulated droplets of the thermochromic liquid crystal material well known in the art. The liquid crystal material is selected to display color within a predetermined temperature range To to T1 and to be substantially transparent (with a "black" or other color backing so as to appear "black" when viewed) at temperatures below To and above T1. The temperature range To to T1 is typically chosen to be the temperature to which a food or food product should be heated, e.g. when heated in a microwave oven, to ensure that any harmful bacteria present in the food or food product is destroyed.For most food products the temperature To should be at least 60"C, preferably above 65"C and typically between from 68"C to 72"C, e.g. 70"C. The temperature T1 may be as high as would be expected to be attained when cooking food in a microwave oven. Since most food contains much water, T1 is practically chosen to be from 95"C to 105"C, e.g. 100"C, but may be from 80"C to 1200C.
The preferred thermochromic liquid crystal material comprises non-sterol chiral nematic liquid crystals.
Information concerning the preparation of blends of such compounds to produce color display over a desired temperature range is disclosed in technical pamphlets published by BDH Chemicals Limited under the titles "Thermochromic Mixtures TM74A,B and TM57A,B" and "Thermochromic Liquid Crystals" by Dr. D.G. McDonnell.
In use, the elongate portion of the food probe, formed by the display strip 7 positioned between the elongate portion 2 and housing part 8, is inserted , pointed end first, into a recently heated food, e.g. food heated in a microwave oven. After a short period of time, e.g. 20 to 30 seconds, sufficient to ensure that the display strip 7 has been heated by the hot food, the elongate portion of the food probe is rapidly removed from the hot food and is immediately observed - i.e. before the heated strip 7 is cooled by the cooler ambient air. Any portion(s) of the display strip 7 containing liquid crystal material heated to a temperature below To will appear black, i.e. the color of the backing strip viewed through the transparent liquid crystal material.Any portion of the display strip 7 containing liquid crystal material heated to a temperature between To and T1 - i.e. between the predetermined temperature range - will appear colored by virtue of the "color" displayed by the thermochromic liquid crystal material. It will thus be appreciated that, immediately after withdrawal of the elongate portion of the food probe from heated food, the display strip 7 will present a temperature "map" of the temperature within the food, any "cool" regions being indicated by "black" regions of the display strip 7 and sufficiently heated regions being indicated by "colored" regions of the display strip 7. Since the liquid crystal material displays temperature over a comparatively wide predetermined temperature range, an "analogue" temperature "map" is obtained along the length of the strip 7.An indication is therefore provided of any "cool" spots throughout the depth of insertion of the probe into the food. The particular colors displayed by the colored portions of the display strip 7 will be representative of the color to which the food product has been heated at the corresponding depth of insertion. The colors at the red end of the spectrum are representative of temperatures near the temperature To and the colors at the blue end of the spectrum will be representative of temperatures near the temperature T1.
Although the temperature range To to T1 will most desirably be the temperature range to which the heated food should have been heated to, it may be that the display strip 7 is sufficiently well thermally insulated that it would take too long a period of time for the display strip to attain at least substantially the temperature of the heated food product. In this case the temperature range To to T1 would be less than the preferred food temperature range. Preferably the display strip 7 will be heated at least approximately to the temperature of the heated food within a relatively short period, e.g. 20 to 30 seconds, after insertion into the heated food.
In an alternative embodiment, the thickness of the elongate portion 2 may not be constant in the region below the recess 6. As shown in Figure 5, the thickness of the elongate portion 2 is smallest along its center line and gradually increases towards the edges of the elongate portion 2. This provides a different degree of thermal insulation beneath the display strip 7 and the central part of the strip 7 will thus respond more quickly than the outer parts of the strip 7 to the temperature of the heated food when the probe is inserted therein. This will provide for a wider range of insertion times in which valid "color" readings are obtained.
Another alternative embodiment is to improve the thermal conduction from the heated food to the display strip. For example, the housing part 8 may be metallic, such as an aluminum plate, and be bonded to the housing part 1. In this case, of course, only housing part 1 would be light transmitting.
Although the display strip 7 preferably includes a continuous layer of liquid crystal material extending therealong, it will be appreciated that the liquid crystal material could be applied in discrete regions, e.g. in the form of dots or rectangles, arranged at spaced apart locations along the length of the strip. Each such discrete region would be responsive over the same temperature range.
Although the elongate portion of the food probe has been described as being generally flat and pointed, it may be of other form, e.g. a cylindrical pencil-like shape.

Claims (15)

1. A temperature-responsive food probe comprising an elongate portion insertable into food and provided with liquid crystal temperature sensing means along its length for sensing the temperature of heated food throughout the depth of insertion of the elongate portion into the food, the temperature sensing means providing a visual indication, at least for a short period of time immediately after withdrawal of the elongate portion from its food-inserted position in the heated food, of any temperature sensed regions of the heated food which are outside a predetermined temperature range having a minimum temperature in excess of 600C.
2. A food probe according to claim 1, in which said minimum temperature lies within the range from 68 C to 72"C.
3. A food probe according to claim 1 or 2, in which the predetermined temperature range has a maximum temperature of which lies within the range 80"C to 1200C.
4. A food probe according to any one of claims 1 to 3, in which the temperature sensing means comprises a thermochromic liquid crystal material.
5. A food probe according to claim 4, in which the thermochromic liquid crystal material displays color when inserted for at least a minimum period of time in food at temperatures within the predetermined temperature range.
6. A food probe according to claim 4 or 5, in which the temperature sensing means comprises chiral nematic liquid crystal material.
7. A food probe according to any one of claims 1 to 3, in which the liquid crystal material has a clearing point at said minimum temperature.
8. A food probe according to any one of the preceding claims, in which the temperature sensing means is surrounded by a thermally insulating material at least part of which is light-transmitting to enable the temperature sensing means to be viewed therethrough.
9. A food probe according to claim 8, in which the thermally insulating material has a varying cross-section perpendicular to the elongate direction of said elongate portion.
10. A food probe according to claim 7, in which the thermally insulating material comprises light-transmitting polycarbonate material.
11. A food probe according to any one of the preceding claims, in which the temperature sensing means is in strip form extending lengthwise along said elongate portion.
12. A food probe according to any one of claims 1 to 10, in which the temperature sensing means is arranged in discrete regions along the length of said elongate portion.
13. A food probe according to any one of the preceding claims, in which said elongate portion includes a metallic sheet means in contact with said temperature sensing means.
14. A food probe according to any one of the preceding claims, in which the elongate portion has a pointed end to facilitate insertion into the food.
15. A food probe constructed and arranged substantially as herein described with reference to, and as illustrated in, Figures 1 to 5 of the accompanying drawing.
GB9109181A 1990-04-30 1991-04-29 Temperature-responsive food probe Expired - Fee Related GB2244132B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB909009668A GB9009668D0 (en) 1990-04-30 1990-04-30 Temperature-resposive probe

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GB9109181D0 GB9109181D0 (en) 1991-06-19
GB2244132A true GB2244132A (en) 1991-11-20
GB2244132B GB2244132B (en) 1994-05-04

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GB909009668A Pending GB9009668D0 (en) 1990-04-30 1990-04-30 Temperature-resposive probe
GB9109181A Expired - Fee Related GB2244132B (en) 1990-04-30 1991-04-29 Temperature-responsive food probe

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Application Number Title Priority Date Filing Date
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2274334A (en) * 1993-01-13 1994-07-20 Margaret Josephine Fogarty Thermometer for use in a microwave
WO1995030136A1 (en) * 1994-04-29 1995-11-09 Visual Indicator Tag Systems - Vitsab Ab Method and device for controlling handling conditions
GB2318870A (en) * 1996-10-30 1998-05-06 James Ronald Hicken Device for indicating adequate defrosting of poultry
GB2346696A (en) * 1999-02-15 2000-08-16 B & H Liquid Crystal Devices A liquid immersible indicating device
EP2026632A3 (en) * 2007-08-17 2010-12-15 Rational AG Method for determining core temperature of cooked food and cooking device to perform this method

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1440292A (en) * 1973-07-02 1976-06-23 Ashley Butler Inc Thermometric element
US4445788A (en) * 1982-04-30 1984-05-01 The Board Of Regents Of The University Of Nebraska Soil probe and method of obtaining moisture, temperature and root distribution of a soil profile

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1440292A (en) * 1973-07-02 1976-06-23 Ashley Butler Inc Thermometric element
US4445788A (en) * 1982-04-30 1984-05-01 The Board Of Regents Of The University Of Nebraska Soil probe and method of obtaining moisture, temperature and root distribution of a soil profile

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2274334A (en) * 1993-01-13 1994-07-20 Margaret Josephine Fogarty Thermometer for use in a microwave
GB2274334B (en) * 1993-01-13 1995-09-27 Margaret Josephine Fogarty Thermometer
WO1995030136A1 (en) * 1994-04-29 1995-11-09 Visual Indicator Tag Systems - Vitsab Ab Method and device for controlling handling conditions
US5857776A (en) * 1994-04-29 1999-01-12 Visual Indicator Tag Systems Ab Method and device for monitoring handling conditions
GB2318870A (en) * 1996-10-30 1998-05-06 James Ronald Hicken Device for indicating adequate defrosting of poultry
GB2318870B (en) * 1996-10-30 2001-03-07 James Ronald Hicken This invention relates to a defrost temperature indicator device for frozen whole poultry birds
GB2346696A (en) * 1999-02-15 2000-08-16 B & H Liquid Crystal Devices A liquid immersible indicating device
EP2026632A3 (en) * 2007-08-17 2010-12-15 Rational AG Method for determining core temperature of cooked food and cooking device to perform this method

Also Published As

Publication number Publication date
GB9009668D0 (en) 1990-06-20
GB9109181D0 (en) 1991-06-19
GB2244132B (en) 1994-05-04

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19970429