Sous vide in a (combi) steam oven

[PedroG]

My old convection oven had to be replaced, now I have a combi steam oven (Electrolux EBSL70SP). Temperature stability is much better than with the old convection oven which oscillated by 13°C around 55°C; the new oven has a sous vide function (100% steam) which allows setting temperature in 1°C increments from 50°C to 95°C, and at 55°C it oscillates within 2°C with a periodicity of about 9-12 minutes; at 75°C it oscillates within 3.4°C with a periodicity of 2.5 minutes.

 

My first experiment was "perfect poached eggs" 16 min at 75°C, they came out the same as I am accustomed to from the sous vide water bath.

 

My second experiment was racks of lamb (vacuum sealed with marinade and mustard about a month ago and kept at 1°C). Thickness was 45mm, so scheduled time was 3 hours at 56°C. Then I unbagged, dabbed dry, painted with HOLL rapeseed oil and started searing in a dry hot pan, but then I suddenly was called away, I returned the unbagged rack on a plate into the oven at 55°C / 100% steam for another 3 hours. After that, drippings on the plate were minimal, I seared the whole rack, cut in 2-bone-chops and seared the cut surfaces, and they came out fork-tender, perfectly pink and succulent as I am accustomed to from the sous vide water bath.

 

My guess is that temperature swings of 2-3°C in a steam oven will affect only the outer few millimeters of the meat which will be overcooked anyway by searing afterwards.

 

Maybe one of our mathematicians can calculate how many millimeters of meat it will take to attenuate temperature swings of e.g. 5°C to e.g. 0.3°C. An earlier experiment showed that core temperature swings are attenuated to within about 0.1°C with temperature swings of 13°C in a convection oven.

 

Another question is how much shorter cooking times will be assuming a heat transfer coefficient above 200 W/m²•K in condensing steam instead of 95 W/m²•K in a water bath as assumed by Douglas Baldwin in his tables. Maybe new tables would have to be calculated for sous vide in combi steam ovens?

 

I may do short time sous vide cooking in the combi steam oven in the future, but for long time cooking I sure will still use my SVM/FMM water bath.

 

[rotuts]

heat transfer in 'steam' is shorter ?

 

its a bit of an oxymoron that there is 'steam' at < 100 degrees C

 

so Id think it was longer as the heating medium is not as dense as water.

[KennethT]

Technically, steam is not < 100degC... that's 'fog'... steam is the clear, vapor form of water, which, when under pressure, can get extremely hot - over 600deg!

 

So, if the machine does produce real steam, and not just hot fog, then when the steam condenses on the relatively colder meat, the most significant form of heat transfer is the latent heat of steam, which is what PedroG was talking about - it is much more powerful than just the circulation of hot water or hot vapor filled air.  This is why steam at 150degC can burn much worse than touching metal heated to 150degC - the condensation of the steam releases a ton of heat all at once - much worse than any conduction burn.

 

ETA: after reading Pedro's description again, though, at 55degC, the oven chamber wouldn't have steam in it anyway... it would be warm fog, which is water vapor that has already condensed - so I don't think the latent heat would be a factor.

Edited November 21, 2015 by KennethT (log)

[KennethT]

Pedro, I was thinking that it should be possible to empirically calculate the difference in efficiency between your waterbath and steam oven.  Do you have any needle probes/foam tape that you can use to measure the core temp of a block of meat as it rises?  If so, you can measure the temp rise at different oven temperatures while comparing to the expected results using SV Dash....  just a bit of homework...

[PedroG]

Specific heat of water is 4.186 J/g/°C whereas latent heat of steam is 2256 J/g, that's why condensing steam delivers more energy than surrounding water.

 

Edit: Oops, the previous posts were faster!

Edited November 21, 2015 by PedroG (log)

[rotuts]

all interesting and good

 

but you state that the temp of the oven itself is 55 C +/- 2 degrees

 

once the oven get to that temp, very little steam   ( i.e.  > 100 C 'mist' ) would be injected Id say, or your oscillations  would be higher

 

its even possible that the + 2 degrees comes from the heat of the steam that's added to the whole oven after condensation.

 

maybe a better idea would be to measure how much condensed liquid water there would be in the 'drip' pan, say, after 2 hours

 

then that would be an approximation of the energy the condensed steam delivered to the oven, mostly to the sides but some to the

 

bags of SV. based on surface area.

 

its an interesting problem  to think about.

 

my CSB at high temps   say 350  condenses very little water after  1.5 hours in the drip tray

 

thats for an average Turkey Meat Loaf.

 

15  cc ?  I have not measured this and the oven is 0.6 cubic feet.

 

just for arguments sake and to further discussion, Im taking the position that 55 degree C water  transfers more energy to the SV bag / minute than

 

55 degreed C in a saturated vapor chamber.

 

as Ive mentioned in the early CSB thread, when steam baking  one has to be very careful when opening the door and no sniffing until the steam is

 

released.

 

Maybe ELX should send me one of these ovens, w a stainless steel enclosure made by them for a 'trial period ? '

 

they would be welcome to come by and pick it up when I was through with it.

 

FD :  I tend to be pretty slow working things like this through

 

also BTW, Im not in any way being critical of ELX or PedroG   I think SV as an option here is fantastic.

Edited November 21, 2015 by rotuts (log)

[rotuts]

KT is correct : the answer lies in the temperature curves of two similar hunks of meat (?) as they rise in 55 C water and 55 C ELX SV

Edited November 21, 2015 by rotuts (log)

[PedroG]

One day I might do a bit of homework as has been proposed.

I plan to repeat the experiment I did six years ago, but with one probe in the center and one just a few millimeters below the surface, doing the same experiment with the same vacuum-sealed pile of wet rags (which in contrast to meat slabs can be reused ad lib) once in the steamer and once in the SVM/FMM water bath.

[rotuts]

"""   in contrast to meat slabs can be reused ad lib ""

 

Meat slabs can be eaten, though !

 

look forward to your findings.