PedroG

Sous Vide Thickness Ruler Version 2 blackp reported a scaling problem when printing Thickness ruler version 1 on a Mac, 70mm being printed as 73.5mm. With my Win7-PC / Adobe Reader 9.3.4 it prints to 71mm. Unfortunately, Excel allows line height adjustments only pixel by pixel. So I now made a cheat, reducing only 3 out of 30 lines from 10 to 9 pixels. Now "Thickness ruler version 2" prints 70mm exactly as 70mm, at least with Win7 / Adobe Reader. Thickness ruler_v2.pdf

As I was still not quite satisfied with the range, I did the antenna hack also on the transmitter: Preparing: remove insulation on antenna arc Bend wire (16.5cm length from soldering point) so it can be threaded around the antenna arc to improve mechanical stability Soldering wire to the antenna arc Receiver and transmitter hacked. Range was a bit better, but after extending the antenna on the transmitter from 16.5cm (quarter-wave) to 66cm (full-wave, on recommendation of Robert Jueneman), it was even better, now connection seems to be stable across a ceiling of reinforced concrete. Although the ET-73 has some drawbacks, it is a (the only?) way to baby-sit a SV-rig and sounding an alarm, should the temperature deviate too much.

Self-explaining: Times are from D. Baldwin's 'A Practical Guide to Sous Vide Cooking' [Moderator's note: I've attached the pdf that Pedro created. Thanks, Pedro! CA] Thickness ruler.pdf

Thanks for the hint! Must have! Ordering it, I found another must-have: Cooking for Geeks: Real Science, Great Hacks, and Good Food by Jeff Potter, which features 25 pages on sous vide out of 400 pages; you may preview the book here.

Sous Vide: Cooking in a Vacuum by Viktor Stampfer (synoptic in English and German). On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee has many informatons relevant for SV, although not specially a SV book.

Heat loss and steady state energy consumption of sous vide cookers Steady state heat consumption of a water bath can be approximated by Steady state power [Watt] = cooling slope [°C/min] * water volume [liter ≈ kg] * 60 [min/h] * 1.163 [Wh/kg/°C] 1.163 Wh/kg/°C is the specific heat of water, i.e. the energy necessary to heat 1kg water by 1°C. Another approximation is steady state power = Hs/(Hs+Cs) * Wn, where Hs = heating slope and Cs = cooling slope and Wn = nominal wattage. Although these approximations do not account for the thermal capacity of the body of the cooker or water-bath, the calculated values reflect effective measured values quite well. I collected the basic data of the same cooker with various insulations and of different cookers. Data of the Tiger have been contributed by blackp. Basic data of cookers were collected by pseudo-open-loop-tuning with the SVM 1500D PID-controller: when the proportional band is set to P=0, then instead of Integral and Derivative one can set hysteresis (I set HY=5°C) which is the range between switching power off and on (bang-bang-control). This allows automatic logging of heating slope and cooling slope. To verify the calculated steady state powers, I tried to measure the power consumption directly with an energy cost monitor, but this did not work with the short energy pulses output by the SVM. So I plugged the FMM-heater to a Variac instead of the SVM, allowing to set the voltage to achieve stable temperature, and I measured voltage and power with two multimeters connected parallel and serial. Here are a few examples from my experience: Cooling slopes were determined at 55°C water temperature and 22°C ambient temperature. Measurements of steady state power confirmed the calculated values. As Nathan says, insulation is the key. Part of the heat loss is caused by water evaporation; with the uncovered FMM, evaporation was about 110ml/h which accounts for a loss of 70W (evaporation enthalpy of water is 0.627 kWh/kg). So covering the bath saves 70W by avoiding evaporation and another 30W by an insulating layer of air. Insulating and covering the polycarbonate container of the FMM may reduce heat loss by a factor of 4 and approximate the insulation of a rice cooker. Using a well insulated beverage cooler instead of the polycarbonate container has the same effect. Just for fun: cooking a suckling pig sous vide in a bath tub is quite energy consuming! Who will contribute the data from a SVS and other SV-rigs? Here is an example of pseudo-open-loop-tuning: Below is the FMM in the same configuration as above, run with continuous power 69V / 2.85A to yield 197W, which maintained 55°C very well. I thank blackp for contributing his data for the Tiger rice cooker and Douglas Baldwin for his suggestion to verify the calculated power values by direct power measurements.

The larger the water volume, the smaller will be the temperature dip when adding cold food. SVP with 1100W may be too weak to heat a bathtub, but with a well insulated vessel you should be able to use pots larger than 30 liters. A reasonable minimum to me seems to be around 7-9 liters.

Hi Oliver, I'll answer your question in the SV-machine topic in a few days when I am back home. Regards Pedro Done, see page__view__findpost__p__1757579

FreshMealsMagic Sous Vide 18L kit Pros: Price (less than SVM + rice cooker or SVS or SWID or IC) Versatility: can be used with any pot like an immersion circulator, from the original 18L polycarbonate container to a beer cooler of any size (28L .... 100L) or even a bath tub (I tried it! See FMM in bath tub). Forced circulation included Uses less space in the waterbath than an IC Polycarbonate container is taller than SVS or laboratory water baths, allowing even larger cuts to be placed vertically "science lab" look may be liked by geeks, see picture below. Cons: Bulky to stow away (IC or SWID is smaller) A mess of cables, tubes, controller, air pump. The junction between the cable and the mantle-tube of the probe has to be immersed in water and may leak, so sensor failures do happen, although there is a 1-year-warranty. A probe with the sensor in a 30 or 40 cm long bendable mantle-tube might obviate this problem, FMS promised they will consider this idea. The air pump may be a bit noisy in a private kitchen environment, although it is said to be a very silent pump. For longtime cooking, it may be turned off as soon as the system is stable. High heat loss with original polycarbonate container, but insulating the container with several layers of bubble wrap plus ping-pong-balls on the water surface will cut the heat loss down to the level of a rice cooker; alternatively use a tall beverage cooler instead of the polycarbonate container. Depending on destination, eventually high shipping costs. "science lab" look may be disliked by people preferring streamlined appliances. I have two SV-rigs, an FMM/SVM1500D and an SVM 1500B with a VEGA 9L/400W sideheater stockpot stirred by an indoor fountain pump. Mostly I use the FMM because ramping up is 15 min compared to almost 1 hour with the stockpot. While one rig is cooking 55°C/48h, I can in the meantime e.g. cook fish at 45°C in the other one. But short-time cooking can also be done with hot tap water in the kitchen sink. Besides you should of course have a camera to post the results of your cooking and plating arts. P.S. Using a GFCI (ground fault circuit interrupter) with any electric equipment where you put your hands in the water is very strongly adsvised.

Hi Oliver, I'll answer your question in the SV-machine topic in a few days when I am back home. Regards Pedro

Any thoughts? There are several misconceptions in this text passage. Feel free to pass this along. Meat is mostly water! There was a classic Star Trek epiosode where an alien species refers to humans as "ugly bags of mostly water" and that pretty much sums up what any animal is (well, the ugly part can be debated). So no matter whether you inject or brine or just use meat as-is, there is plenty of water in the meat to evaporate. In the case of brisket it is about 71% water. The method of heating the meat does not matter, the same effect occurs for both radiative and convective heating. Now, as it so happens, radiant heating plays essentially no role in most barbeque, because radiant heating is only important when there is a high temperature source. Most barbeque is smoked with an air temperature (dry bulb) of 90C/194F to 110C/230F. At those tempertaures radiant heating is insignificant. Most barbeque rigs / smokers have the fire baffled so the meat does not directly recieve IR radiation from it. South American asado (from Chile or Argentina especially) does use radiant heat, but that is a very different method. However, even if there was radiant heating, it wouldn't matter. The point about wet bulb temperature is that evaporating water takes energy, so a wet surface that is evaporating will be cooler than a dry surface. It doesn't matter how you heat it, if the surface is wet, then it will be cooler than a dry surface if water can evaporate. When he says that wet bulb / dry bulb is about gas, I think there is some confusion. Wet bulb temperature is the temperature of a wet surface which is cooled by evaporation. It is a surface temperature. The air temperature is the dry bulb temperature. The reason that "gas" (i.e. air) is involved is that in order for the water to evaporate it must go into the air. If the air is already "full" of water (meaning that relative humidity is 100%) then evaporation can't occur. Anybody who sweats knows this - sweating is done to take advantage of evaporative cooling. The reason that we feel more uncomfortable in high humidity is that our sweating doesn't work as well. I am not sure that he understands that the temperature tests I did were not in a water bath. I took a vacuum sealed brisket and cooked it next to an uncovered brisket, but they were in the same oven. The sous vide bag simply stopped the evaporation. There is a TINY effect due to collagen, but it is so tiny that it does not show up unless you use a differential scanning calorimeter. If there was a large collagen effect, then we would see it in the temperature profile for the sealed brisket with no evaporation. But we don't. The test I did was in a convection oven, but a "free draft wood smoker" will not change anything. Water still evaporates! The existence of some smoke in the air won't stop water from evaporating. The smoke build up on the surface of the brisket may hinder evaporation slightly. The free draft part means that the smoker would, if anything, have a lower humidity than in the convection oven because the convection oven recirculates air to some degree while the smoker may, or may not depending on how open the dampers are. The amout of draft in the smoker, the way air circulates, how full the smoker is, the dry bulb temperature in the smoker, the relative humidity of the air outside the smoker will all make small differences. That is why different people report a "stall" of different temperatures and durations. The humidity outside the smoker has some effect, but only a small effect. The hotter air is, the more water it will hold. If you take air and heat it up to 90C/194F to 110C/230F, it will be very low relative humidity, no matter how moist the air outside is. Finally, he can find no reference supporting what I am saying here because, as far as I know, nobody has explained the BBQ "stall" this way before. It is a new explanation. I suspect that some food scientist somewhere may well have figured this out, but I am not aware of any. But that doesn't mean it is wrong - it just means it is new. The paper he quotes from Journal of Food Science supports ALL of what I am saying, by the way. It is a good early article on the topic of roasting meat. It confirms that there is substantial evaporative losses, and it confirms that the meat cooks with the surface at the wet bulb temperature. I totally agree. The BBQ brother should be invited to repeat Nathan's experiment in his BBQ smoker with two cuts of brisket, one naked and the other wrapped in cling film to avoid evaporation (vacuum-sealing is not necessary). To try to visualize the collagen-melting-stall he might use a bunch of beef achilles tendons glued together with transglutaminase, wrapped in cling film to rule out evaporation cooling.

I used to exclusively use a VERY hot pan (somewhere around 700F) for searing but for many cuts of meat I find that a torch works better for developing crust without cooking the meat and even for cuts with an even surface (like rib eyes) I have switched to a torch because the result is just as good as with a pan and there is much less work involved. Do you get less smoke when using a torch instead of a pan? I use a pan right now and the main problem is that the hood above the stove is ancient and practically useless (rental so there isn't much I can do about that), which means that the kitchen quickly fills up with smoke. Yes, there is less (much less) smoke using a torch. No chance, SWAMBO does not allow a blowtorch in the kitchen. For minor surface irregularities I use ample oil, and for complicated surfaces I use tongs to hold the meat in all the necessary positions. I use a special non-stick skillet that supports extremely high temperatures, so cleaning is no problem. And I do not mind overcooking the outer 2-4mm, it gives the meat a more traditional temperature and texture gradient to suite my wife's taste.

I believe that the temperature is somewhere in the 2800 to 3100 F range -- so hot that if you aren't paying attention, you will turn the outside into something resembling charcoal. They burn hotter and with a more useful flame area than a heat gun. The flame of the Iwatani is very controllable. And don't be fooled by the pictures on the web, these aren't wimpy little creme brulee torches (although if you are making creme brulee it would be an awesome tool for the job). It is more powerful than my bernzomatic propane torch which has been retired for cooking since I got the Iwatani due to the more controllable flame and lack idiot-proofness as far as gas-aftertaste (the taste that people mention with propane happens if you hold the torch too close to the meat which results in spraying the meat with some uncombusted propane). Btw, while a heat gun doesn't use a gas canister it uses lots of energy. Electricity is a much less efficient way to generate heat than burning gas. Butane blowtorches achieve about 1400°C/2500°F. Wagner HT3500 heat gun is said to achieve 730°C/1350°F, but was recalled in 2009 Rice bran oil has smoke point 247°C/475°F, heat transfer is much faster than hot air or flame.

Sous vide rigs may fail, so there should be an alarm when temperature deviates from the set-point. Lately it happened to me that the FreshMealsMagic triggered the GFCI (ground fault circuit intterrupter) and bath temperature dropped from 49°C to about 48°C during 2h20' cooking. This did not cause me any problem, but if it happens during a 48h-cooking without being noticed, you have to discard your food. It may also happen that a sensor fails or shifts and bath temperature rises or drops. As my SV-rig resides downstairs in the air-raid-shelter, I looked for a way to baby-sit my SV-rig without going downstairs every hour, and when ordering Nathan's book at Amazon, I also ordered a two-channel remote smoker thermometer Maverick ET-73 which arrived yesterday. It has a channel for the food temperature with a high-alarm and a channel for the oven temperature with high- and low-alarm; the latter can be used to sound an alarm whenever the bath temperature goes outside your set limits. A known issue with the ET-73 is poor range, especially through walls. I had to place the receiver on the kitchen floor as near to the transmitter as possible to get a signal. So I hacked the receiver and did the Maverick ET-73 Range Modification From LilSmoker with a small modification shown in the pictures below, soldering the antenna wire to the rear side instead of the front side of the small PCB with the horseshoe shaped circuit board antenna, so the antenna wire does not have to be bent to exit the case. Now the range is sufficient to place the receiver anywhere in the kitchen and have a good signal. It's far from the 100 feet that Maverick claims, but an air-raid-shelter is a bit of a Faraday cage, so I am satisfied with the result. It is possible to make a similar modification on the transmitter, see http://www.instructables.com/id/Increasing-the-Range-of-a-Wireless-BBQ-Thermometer/, but in my case this was not necessary. 0.7mm SS antenna wire soldered to the rear side of the small printed circuit board Small PCB replaced after soldering the antenna wire to its rear side Length of the antenna wire measured from the soldering point has to be exactly 6.5" / 16.5cm which is the quarter wavelength of 433MHz Small notch in case to accommodate antenna wire The end result.

Thanks, Nathan! This is very illustrative. I think with your and Douglas' post everything has been said. BTW a Rational 61 SCC (7336 EUR) seems to be out of the reach of a home cook, but its temperature stability within 1°C is impressive.

Peter, every time I see one of your oven graphs, I wonder when you are going to improve the control on that oven of yours! A 15C swing ... ! I'm sure its towards the better end of the population, but nevertheless, I wouldn't have expected YOU to put up with that for this long! dougal, I am happy to have my SV rigs better than ±0.1°C (usually ±0.07°C). SWAMBO is extremely reluctant to change our 15-year-old bang-bang-controlled convection oven for a combi-steam-oven (do they have PID-control nowadays?), and I am not going to tamper and tinker with the electronics of that oven, as I never had adverse effects and noticed these temperature swings only when I started doing sous vide and measured the oven temperature with a digital thermometer; anyway, as you see in my earlier posts, and as Douglas Baldwin just pointed out, the surface heat transfer coefficient for a convection oven is so poor that inside a water-pot or roast or braise or whatever food you put in the oven, these temperature swings are attenuated to a well acceptable level. At higher temperature settings, the oscillation periods are even shorter than the 12-19 min I described in my earlier post, namely about 6.5 min (with a 14°C swing) at 200°C (due to faster cooling by higher heat loss at higher difference oven-ambient). Pedro

Would you mind posting the graph? Thank you.

Some time ago I did an experiment showing extreme evaporative cooling: I soaked a wet pile of rags about 10cm thick with water of 50°C and placed it in my convection oven set to 50°C. One temperature sensor was placed in the center of the rags, the other was placed in the oven near the pile. Evaporative cooling made the core temperature of the package drop to 36°C, then I lost my patience and wrapped the pile in cling-film to stop evaporation (which corresponds to completely drying the surface of the meat by blow-torching), and temperature rise to the final core temperature took about 6 hours which is in the 4-8h range described by Heston Blumenthal in his non-SV two-bone-fore-rib (From The Sunday Times, November 12, 2006, "Steak with blue-cheese-infused butter and mushroom ketchup"). Evaporative cooling not only kept the core temperature lower, but also lowered the oven temperature.

Hi Nathan,thank you for your profound explanations. If your wet bulb / dry bulb hypothesis is correct, this temperature stall would happen in a BBQ oven, but not if you cooked an identical cut of meat sous vide (or braising btw) at a water temperature higher than 74°C. Did you do the experiment? If memory serves me, collagen is enzymatically converted to gelatin by collagenase, which gets inacivated at about 60°C; a slow process which takes one to several days depending on age-related cross-linking of the collegan. At or above 60°C collagen fibers which have not yet been enzymatically converted to gelatin will swell and shorten (a process reversible by cooling or stretching of the fibers) and squeeze liquid out of the muscle fibers. At about 74°C collagen undergoes a physical phase transition (like melting ice) which is much faster than the enzymatic conversion to collagen, and which would explain the temperature plateau. Please correct me if I am completely wrong.

Sous-vide without buying expensive equipment What items you need A pot of about 8 litres that will fit in your electric oven A digital thermometer with an immersion probe (1°C resolution is sufficient to begin with, 0.1°C is better) Ziploc bags large enough to accomodate your cut of meat A hole punch A metal skewer a few centimeters longer than the diameter of your pot Paper towel Oven gloves A heavy cast iron skillet Vegetable oil Calibrating your equipment Find the oven temperature setting that will yield a water temperature of 55°C, cf. previous post How to cook measure the thickness of your cut of meat, as thickness, not weight is the factor indicating the cooking time (2cm - ½ hr., 2½cm - ¾ hr., 3cm - 1 hr., 3.5cm - 1½ hrs., 4cm - 2 hrs.) preheat your electric oven to the temperature needed to keep the water at 55°C (in convection mode if available) punch two or three holes in the upper rim of the Ziploc bag with your meat, thread the skewer through the holes, and hang the bag in the pot, placing the skewer over the rim of the pot, fill the pot with hot tap water of 55°C (measure with your immersion thermometer) until just below the zipper of the bag, so that the meat is completely immersed. repeatedly check the water temperature to remain between 54-56°C. cooking times indicated above are minimum times to reach core temperature, they may be prolonged by 1-2 hrs. until you are ready with the rest of your meal. Heat your heavy cast iron skillet with vegetable oil until just smoking Take the meat out of the Ziploc bag, dab dry with paper towel, and give it a short sear (15-30 seconds per surface) to give it a nice brown crust. Refine your cooking method find out what core temperature suits your taste best if your preferred temperature is below 55°C, you should restrict your cooking time to a maximum of 4 hrs. for safety reasons (microbial contamination); above 56°C you may use longer cooking times (a 70mm thick roast requires 6 hrs. cooking time) if you like, marinate your meat before bagging if you come to like sous vide cooking, be prepared to spend some money for the appropriate equipment to use more exact temperature control and longer cooking times (maybe 24-48 hrs.) in a "shoot and forget" manner; with the oven-waterpot-method you may have to check the temperature every 15 or 30 minutes to keep it constant, and with cooking times longer than 4-6 hrs. water evaporation will become an issue. Measuring thickness of the meat. Closing immersed Ziploc bag, squeezing out all air. See also Douglas Baldwin's video on youtube Ziploc bag threaded on skewer to secure vertical position and avoid floating.

Temperature stability with a water-pot in an electric convection oven Before I bought a SousVideMagic and an electric stockpot, I started cooking sous vide just with a pot of water in the electric oven, and the results in texture and taste (fork-tender, succulent and juicy) were convincing me to invest some money for dedicated equipment. In that time I used a stainless steel pan with about 2 litres of water, as I was not yet aware that a large water volume and a tall pot are advantageous, giving better temperature stability and better submersion of bags. Now I conducted an experiment on temperature stability with a large enameled pot with 7 litres of water in my electric convection oven: I started with hot water from the tap at 57°C with the oven set to 75°C, and it took about three hours to come to the final temperature of 61.8°C, then the water temperature stabilized within ±0.1°C, the small oscillations following the ±9°C oscillation of the oven temperature (ON/OFF-controller, no PID!). This shows that good temperature stability is possible without a PID-controller, but ramping up in the oven is much too slow, the desired water temperature has to be adjusted by adding boiling water as necessary. 61°C may do for poultry, but for beef I prefer 55°C or less, so I set the oven to 65°C and added a few ice cubes to reduce the water temperature. It stabilized at 55.7±0.1°C. To simulate adding a frozen cut of meat, I dropped an ice-brick of 460g/-20°C in the water, which led to a temperature drop of 7°C with much too slow temperature recovery (several hours). This shows that the temperature drop by adding a bag with food has to be corrected with hot water, although adding a bag with a pound of meat from the refrigerator (5°C) would induce a less hefty temperature drop than a frozen one. 55.7°C is still more than I like, so I continued the experiment with the oven set to 60°C. Temperature climbed to 54.5°C±0.2°C and remained stable for four hours. At lower oven temperatures, the difference between oven temperature and water temperature was smaller and the oscillation period was longer (12 min. at 75°C, 19 min. at 60°C), both maybe due to less evaporation cooling, and the oscillation amplitude of the water temperature was somewhat higher, maybe due to the longer oscillation periods. I remember that when I used a smaller stainless steel pan, the difference between oven temperature and water temperature was higher than with the tall enameled pot, about 20°C. With the tall pot, the water surface (evaporation cooling) is smaller relative to the outer surfaces of the pot, so there will be better heat transfer to the pot as a function of a larger heat-transferring surface and maybe due to less reflection of heat by enamel compared to stainless steel. Conclusions: Sous vide cooking with good temperature stability is possible with a large water-pot in an oven, provided the oven can be set to such low temperatures. (If not, keeping the oven door open by one or a few centimeters may reduce the air temperature in the oven). Longtime-cooking (e.g. 48 hours) needs some baby-sitting, as loss of water volume by evaporation may be an issue (covering the pot would prevent evaporation cooling and change the equilibrium between oven temperature and water temperature), and some ovens switch off after 12 hours or so for safety reasons, necessitating a restart at regular intervals. The target water temperature has to be adjusted by adding cold or hot water, as heat transfer from the oven to the water is too slow (which has the advantage of good temperature stability despite considerable temperature oscillation in the oven). Before starting sous vide cooking, the necessary oven-temperature setting for the desired water temperature has to be determined experimentally; a data logger is not necessary for this purpose, a digital thermometer (with a cable probe), pen and paper will do.

Although it is listed in Amazon.com, it is not sold by Amazon but by Eades Appliance Technology LLC which is in fact http://www.sousvidesupreme.com/shop/cookbook who obviously do not sell anything outside America. Douglas was so kind to send me a copy directly (thanks a lot, Douglas, for all your work you have done for our community!). Regards Pedro

I prefer my salads to be lightly coated with olive oil and aceto balsamico instead of being drowned in a sauce. So for a salad prepared in the bowl, it's sprinkle (EVOO), toss, sprinkle, toss, sprinkle, toss, spice, toss, salt, toss, herbs, toss, spray balsamico, toss. I start with oil to prevent osmotic dehydration by the salt. For a salad that is directly arranged on the plates like insalata Caprese, sprinkling EVOO is also preferable over pouring, and I then often use balsamico reduction (30% of original volume) in a 1ml-syringe with a blunt needle:

I had to clean my Cuisipro Mister (or Mistress, for political correctness?) again and did it like Sparrowgrass described, and it works like a charm, sprinkling my salads every day (I prefer a sprinkle over a mist wafting all over the kitchen). I never had a problem with rancidity using EVOO from Tuscany.

Thanks, Nathan, for your clarifying post, and for your hints concerning visualization of convection currents. I have conducted a few experiments confirming the importance of adequate positioning of the bag in the bath, see Sous Vide Wikia The conclusions are: * An uncovered water bath may lead to uneven temperature distribution by evaporation and consequent evaporation cooling of the superficial water layers. * Uneven temperature distribution happens especially with insufficiently submerged items in horizontal position. And my recommendations are: * An open water bath should be covered by a plastic cover, hollow plastic balls (ping-pong balls), a styrofoam cover, or whatever, to avoid evaporation and consequent evaporation cooling of the superficial water layers. * Vertical positioning of bags avoids the insufficient submersion that may occur with horizontally placed bags, and in case of multiple bags, it does not impede natural convection. * A tall water bath as opposed to a shallow bath has the advantage of allowing even large pieces to be positioned vertically. * Forced circulation (pump or aquarium bubbler) is desirable especially in shallow water baths (useful water depth less than 20cm, like laboratory water baths or SousVideSupreme). * Bags floating horizontally in an unstirred and uncovered water bath must be avoided, as this may lead to uneven heating of the food, which is especially important in pasteurizing food. If horizontal placement is inevitable, adequate submersion must be ensured. Furthermore, natural convection currents are very weak as soon as steady state has been reached and heating power is minimal, see http://www.mydrive.ch/download/75349494/Heating_Full_Power_2000W.AVI http://www.mydrive.ch/download/75350734/Steady_state_55C_no_cover.AVI http://www.mydrive.ch/download/75352148/Steady_State_55C_with_cover.AVI username: visitor@P.Gruber password: visitor