Technology Report Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX
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Economical High-Temperature Water Bath Control and Monitoring with a Sous Vide Cooking Device Thomas R. Rybolt* and Robert C. Mebane
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Department of Chemistry and Physics, University of Tennessee at Chattanooga, Chattanooga, Tennessee 37403, United States ABSTRACT: A low-cost alternative to the typical scientific laboratory water bath or a hot plate stirrer water bath is proposed. Readily available immersion circulators have been developed for sous vide cooking. These precision cookers are designed to maintain water at an exact temperature and thus are well-suited for the similar laboratory requirements of a stirred water bath. It was found that these devices can maintain a laboratory water bath within ±0.1 °C.
KEYWORDS: Upper-Division Undergraduate, Laboratory Instruction, Hands-On Learning/Manipulatives, Laboratory Equipment/Apparatus, Thermodynamics
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INTRODUCTION Temperature controlled water baths are used in a wide variety of laboratory settings and have been the subject of articles in this Journal over many decades.1−11 A precisely controlled constant temperature water bath can be accomplished by the use of a scientific water bath with a means to set and monitor temperature. Alternatively, an approximately controlled water bath can be accomplished by a beaker of water on a hot plate stirrer. The temperature of the water in the beaker can be monitored with a digital thermometer, but achieving and holding the desired temperature requires frequent observations and adjustments. We would like to suggest an alternative means of controlling a water bath that is significantly less expensive than either a scientific water bath or even a hot plate stirrer. The type of device under consideration typically can be used to heat up to 12 L of water, has a digital setting up to 99.9 °C, has excellent temperature control with a reported precision of ±0.1 °C, has a digital display of actual temperature, has a propeller on a shaft to effectively stir the hot water, and with a convenient clamp is held down in the water so all the heat (unlike a hot plate) goes into the liquid. The specific device to which we are referring is a sous vide (soo ˈved) ̅ culinary precision cooker also known as an immersion circulator. The poaching of food involves cooking food in a liquid, usually water, that is maintained below the boiling point of the liquid.12 This cooking technique was elevated to culinary heights in the mid-1970s with the sous vide method.13−15 Sous vide, or under vacuum, involves placing raw food in vacuumsealed bags and immersing these bags in a circulating water bath while maintaining precise temperature control to cook the food to a perfect doneness while maintaining moisture, flavors, and aromas. Once relegated to only high-end restaurants © XXXX American Chemical Society and Division of Chemical Education, Inc.
because of the expense of the water baths, sous vide cooking is now available to the home cook with the introduction of moderately priced portable temperature controlled immersion circulators. Various models of sous vide precision cookers are readily available through online retailers or in stores selling culinary and kitchen appliances. These devices (currently around $100) are only a fraction of the cost of hot plate stirrers or commercial scientific water baths. The advantages of the sous vide immersion circulators for laboratory water baths are convenience and good temperature control at economical prices being in the range of 8−20 times cheaper than typical scientific water baths. Expensive water baths have advantages of their devices incorporating insulated containers, fitted covers, and stainless steel interiors, and they may have options for shaking and convenient pumps for external circulation. Hot plate stirrers or heating mantles are suitable for beakers or glassware where reactions may be taking place. However, there are many lab situations where the inexpensive sous vide immersion circulators can provide the needed temperature control with good precision and accuracy for useful laboratory water baths.
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MATERIALS AND METHODS The specific model that we tested (ANOVA Precision Cooker) had LED displays for current and set temperatures and a numeric scroll wheel to set temperature. This model also includes a free smart phone app utilizing Bluetooth to turn on and off the device as well as set and monitor the temperature. It is cylindrical in shape with a 7 cm diameter, a 37 cm height, Received: March 7, 2018 Revised: June 5, 2018
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DOI: 10.1021/acs.jchemed.8b00163 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
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Technology Report
RESULTS AND DISCUSSION The accuracy of the sous vide immersion device used in this study was verified with a NIST-Traceable ThermoWorks ThermaPen. The temperature difference between sous vide thermocouple and the ThermaPen over five different temperatures did not deviate more than 0.1 °C (10 L water heated to 30.0, 40.0, 50.0, 60.0, and 70.0 °C). Many sous vide manufacturers report that their thermocouples are calibrated back to a scientific platinum resistance thermometer primary standard with accuracy of ±0.1 °C. While a sous vide immersion circulator is designed so it may be clamped directly to a large pot for cooking, a polycarbonate container can be purchased for cooking that can function as a hot water bath container. We tested a 12 L one in lab, and it worked fine as a water bath holder (see Figure 2). However,
a mass of 1.1 kg, a heating output of 800 W, and a propeller that effectively circulates the water at a rate of 8 L per minute. There is a stainless steel skirt around the portion that extends into the water. The listed temperature range is 25−99 °C. It also comes with an adjustable ring clamp to hold the immersion circulator in place. The devices sold in the United States may come preset to Fahrenheit, but the temperature can be changed from Fahrenheit to Celsius. On the device we tested, this change was accomplished by holding the on button for 10 s. This information was available on the device information Web site. The bottom cap and exterior metal skirt can be removed to access the heating coil, temperature probe, and propeller shaft for cleaning or examination (see Figure 1).
Figure 1. Sous vide immersion circulator with bottom cap and metal cover removed to show heating coil, stirring propeller, and temperature probes. Figure 2. Sous vide device set and reading 50.0 °C in 12 L polycarbonate container used for the water bath. Erlenmeyer flask included to demonstrate use of bath.
The type of temperature probe (Vernier LabQuest) used to monitor the water bath temperature (changing or fixed) with time has a reported accuracy of ±0.2 °C near 0 °C and ±0.5 °C near 100 °C. These temperatures were compared to the sous vide readings.
we were interested in something with better insulation. Because of its convenient size, an 11 L cooler was used (see Figure 3). Both the handle and top were removed by prying loose at the hinge points. Similarly sized coolers can provide convenient hot water bath holders. The cooler can be used as a water holder directly, or alternatively, a ring stand and a large beaker (2 or 4 L) can be placed into the cooler and an immersion circulator placed into beaker (clamped on the cooler not beaker). Alternatively, if more access is needed, the sous vide device can be clamped on the outside of a cooler while the beaker is placed beside the cooler. There are minimum and maximum water levels marked on the sous vide cooker. The minimum and maximum water level marks are at 5.3 and 15.0 cm from the bottom of the sous vide device, respectively. So, the water must be at least 5.3 cm deep, but the device can be raised; the maximum water level can be as high as needed. Whenever the tested device is turned on to
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SAFETY Only water should be heated with sous vide immersion circulator. No flammable liquids or volatile compounds should be used with this electric device. Although sous vide cookers can operate unattended, we do not recommend this for overnight laboratory usage. Only the bottom portion of the cylindrical device should be placed in water, and the water level should be between the marked minimum and maximum levels. The use of tap water and not distilled or deionized water is recommended by sous vide manufacturers. The user of a sous vide immersion circulator should carefully read the operating manual that comes with the device with particular attention given to any noted precautions. B
DOI: 10.1021/acs.jchemed.8b00163 J. Chem. Educ. XXXX, XXX, XXX−XXX
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control temperature, its rotary circulator moves an equivalent of 8 L of water a minute so it provides effective stirring of a water bath. All commercially available sous vide immersion devices come with a motor driven propeller system for water circulation purposes. Various setups as described above were tested, and all worked well with 1.4−11 L of water held at 35.0, 50.0, or 85.0 °C. Once the set temperature was reached, the temperature remained steady within ±0.1 °C for the test period of 1 h. For temperature comparisons, an external device with either thermocouple probe or standard temperature probe (using default calibrations) placed into the water and away from immersion circulator agreed with the sous vide water setting and reading of the tested precision cooker. In one shorter comparison, 1.4 L of water in a 2 L beaker was heated with the cooking device, and it took about 8 min to bring the temperature from 22 to 50 °C. The same amount of water on the hot plate stirrer set at 300 °C and 300 rpm took 15 min to come to 50.0 °C. The temperature of the sous vide immersion circulator heated water agreed within 0.1 °C over the test period of 2500 s. Using the noninsulated polycarbonate container shown in Figure 2 and the insulated container shown in Figure 3, 8 L of tap water was added to each bath. After a slight initial heating, each sous vide device was turned off and the water equilibrated to about 25.4 °C. A covering of aluminum foil was placed around the top of each bath to reduce water loss, and then each 800 W sous vide device was turned on and its temperature set to 85.0 °C. Two temperature probes were
Figure 3. Sous vide device set and reading 85.0 °C in 11 L insulated food cooler used for a water bath. The separate temperature probe to the right was used to provide an independent temperature reading.
Figure 4. Heating curves for temperature (°C) versus time (minutes) for 8 L of water in an insulated container (example shown in Figure 3) and 8 L of water in a noninsulated container (example shown in Figure 2). After equilibration of baths to an initial temperature about 25.4 °C, then the two 800 W sous vide immersion circulators were set to 85.0 °C and heating started. The noninsulated heating data is offset by 5 min and starts at 10 min so both curves can be clearly seen. C
DOI: 10.1021/acs.jchemed.8b00163 J. Chem. Educ. XXXX, XXX, XXX−XXX
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(4) Knox, W. J. The construction of an inexpensive constant temperature water bath for solubility measurements. J. Chem. Educ. 1938, 15 (7), 343−344. (5) Loveless, W. M.; Marshall, M. L. A constant-temperature bath for warm climates. J. Chem. Educ. 1952, 29 (3), 137. (6) Slagle, J. R.; Wendlandt, W. W. A constant-level water bath for the student laboratory. J. Chem. Educ. 1956, 33 (7), 330. (7) deBruyne, N. A. Controlling thermostated water baths near room temperature. J. Chem. Educ. 1971, 48 (6), 416. (8) Dewhurst, F.; Green, K. L. An inexpensive shaking water bath. J. Chem. Educ. 1972, 49 (10), 701. (9) Greig, D. G. T. A simple sample holder for use in thermostat tanks. J. Chem. Educ. 1975, 52 (8), 549. (10) Mercer, G. D. Low-cost water-bath temperature controller. J. Chem. Educ. 1992, 69 (7), 568−569. (11) Sundheim, B. R. Modelling a thermostated water bath with a spreadsheet. J. Chem. Educ. 1992, 69 (8), 650−654. (12) McGee, H. On Food and Cooking, The Science and Lore of the Kitchen; Scribner: New York, 2004; p 162. (13) Keller, T.; Benno, J.; Lee, C.; Rouxel, S. Under Pressure, Cooking Sous Vide; Artisan: New York, 2008. (14) Baldwin, D. Sous Vide Cooking: A Review. Int. J. Gastronomy and Food Science 2012, 1, 15−30. (15) Hesser, A. Under Pressure. New York Times Magazine. August 14, 2005. http://www.nytimes.com/2005/08/14/magazine/underpressure.html (accessed June 2018).
present in each bath at about 10 cm from the edge of the sous vide heater, and the tip of each probe was at a water depth of about 5 cm. Temperature data was collected from all four probes at 5 s intervals, and each pair in the same bath were averaged. The resulting heating curves are shown in Figure 4. The noninsulated data is offset delayed by 5 min on the plot so both curves can be clearly seen. The temperature rise rate was almost identical for each bath except at higher temperatures where the uninsulated container took slightly longer to reach the set point of 85.0 °C. To heat 8 L of water from 25 to 85 °C took about 60 min for the insulated container and about 65 min for the noninsulated container. So, generally it is about 10 min to heat 8 L by 10 °C. The temperature probes (Vernier LabQuest) used to record this data have a reported accuracy of ±0.2 °C near 0 °C and ±0.5 °C near 100 °C. The sous vide devices each showed the bath temperatures stabilized at 85.0 °C. The insulated bath probe temperature also steadied at 85.0 °C while the noninsulated bath had an upper probe temperature of 85.6 °C. It is useful to note that readily available sous vide immersion circulators range from 800 to 1200 W. The higher wattage devices would significantly shorten wait times for a water bath to heat to the set temperature. Alternatively, two sous vide devices could be used simultaneously to speed up heating of a larger volume water bath. In our Physical Chemistry I lab, water baths are used for heating test tubes to melt octadecanol and camphor mixtures for subsequent freezing point depression determinations, for a heat of vaporization determination from a van’t Hoff plot, for heating an acidic sucrose solution as part of a sucrose inversion order of reaction determination, and for water flow through a polarimeter cell for an energy of activation experiment. Historically, we have used two hot plate stirrers and two scientific water baths for these experiments. All these water bath needs can be accomplished by use of sous vide immersion devices. External water flow at moderate temperatures, if needed, may be accomplished by immersion pumps such as those used for aquariums.
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CONCLUSION While these devices are designed for cooking, the sous vide requirement of precise temperature control ensures that these immersion circulator devices are well-calibrated and maintain a stable temperature over long periods. Readily available sous vide cookers can provide a viable and inexpensive means to maintain a laboratory water bath.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Thomas R. Rybolt: 0000-0002-4059-4048 Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Wilson, N. F.; Carleton, R. K. A constant level water-bath. J. Chem. Educ. 1929, 6 (8), 1335−1336. (2) Hormisdas. Modified water-bath thermostat. J. Chem. Educ. 1933, 10 (9), 576. (3) Yohe, G. R.; Keckler, C. G. Constant-level siphon for a hot water bath. J. Chem. Educ. 1934, 11 (8), 462. D
DOI: 10.1021/acs.jchemed.8b00163 J. Chem. Educ. XXXX, XXX, XXX−XXX
