Sous Vide: Recipes, Techniques & Equipment, 2011

Chris Birkett · June 6, 2011

Sure looks like galvanic corrosion. Try a marine outfitter (e.g., West Marine) for a zinc anode. Changing the water in the tank might help some too.
The vendor could put in a back-bias that counteracts the corrosion potential, but probably won't.

I don't generally store water in the tank when it's not in use, so changing the water wouldn't help. The tap water here is very hard (25 gpg or ~430 ppm), but softened with an ion exchange unit. If this is galvanic corrosion then wouldn't the stainless food rack be involved? It's been my impression that the worst spots on the grill are from where it is in contact with the rack, but it could be my imagination.

dougal · June 6, 2011

I already confirmed that the marks are corrosion rather than mineral deposits, as did the other owner I mentioned. If you examine it closely it is obvious the surface is corroded and there is material missing. In some parts on the bottom it's very easy to spot because the edge of the metal is thinned.

That is corrosion.

Its unsightly but should be harmless.

Simplest way to stop it would be to (electrically) insulate between the different metals.

Its caused by different metals being in electrical contact with each other, while immersed in a conductive fluid. Even de-mineralised water is going to be somewhat conductive ...

So, break the electrical contact with insulation.

As regards insulation, I'd suggest you cut up a silicone baking mould (or maybe ice cube tray).

Baking silicone should be food-safe-and-stable at any expected temperature.

You want the smallest disruption to convection currents in the water, so only insulate points of contact between dissimilar metals.

Paint or varnish could do the job. And, with the food well sealed in bags that are dried off before opening, ought not to cause any hazard.

The expectation has to be that electrical insulation between the heat spreader and the heated bottom of the tank won't interfere "much" with the aluminium's function of diffusing the heat evenly across the bottom of the bath.

But it does look like a really, really basic product design error ...

Apart from changing the material's spec, or insulating between the different metals, or providing a "sacrificial anode" (like zinc to take the hit), the only mitigation advice would be to empty the thing between uses, and store the metal internals DRY.

Chris Birkett · June 6, 2011

One of the cost-saving measures for the Demi is replacing the stainless tank and bottom grill of the regular Sous Vide Supreme with anodized aluminum. However, the crappy food rack they supply with it, as well as the optional "universal" rack are both stainless steel, and sit directly on the aluminum grill. If this is causing galvanic corrosion in regular tap water then it is a pretty major design flaw, IMO.

I don't store water in my Demi, so this has happened with only four months of regular use. It extends below the grill to the bottom surface of the tank itself, and I assume it will continue to get worse if I don't make some DIY modifications.

DocDougherty · June 6, 2011

One of the cost-saving measures for the Demi is replacing the stainless tank and bottom grill of the regular Sous Vide Supreme with anodized aluminum.

Somebody can always find a way to make a product for a little less, and there will always be a market for it. Whirlpool has been selling Kitchen Aid mixers in that environment for many years and is losing repeat customers as a result. I suspect the same thing will happen with sous vide equipment. Circulators are expensive to make and somebody figured out how to get rid of the pump by letting free convection substitute, at some loss in temperature uniformity.

Thanks for pointing out this particular design flaw. There are coatings (other than anodizing) that will work, and there are aluminum alloys that are more resistant but perhaps harder to work and more expensive and thus less desirable from the perspective of the manufacturer. Products will evolve in the face of market pressure and the sous vide market is still quite small and young. This kind of discussion probably accelerates change.

rotuts · June 7, 2011

Sous Vide meat for a sandwich: chance discovery

as the sandwich thread just started, i got hungry and pulled out a Sous Vide chunk of pork loin for a sandwich. I cut up the whole loin into pieces to fit my 6" 10" SV bags. I then put varioius rubs on them and SV at 130. this cut was from the frontal end that has the darker and lighter muscles.

this chunk was fairly tight in the bag, and as I put the meat back in the bag then into the refirg, i cut this thin With The Grain so it would be narrow-er on the refit.

as the meat was tender from the SV, it turned out the texture of the sandwich was much better than the cuts Ive always made against the grain, which are not as tooth-some

has anyone else noticed this?

mcdiarmid · June 8, 2011

I would like some suggestions regarding length of time to do shredded beef sous vide. I have a shredded beef recipe that I use for tacos/fajitas which is cooked at low temp for 16 hrs or so using the crockpot. However, it is always a bit more dry than we like and I thought of doing it sous vide (with the advantage of par cooking a batch for future meals as well). I plan on using a chuck or blade roast as my base meat. The beef will be in a chipolte pepper (with lime/vinegar base) sauce while cooking (but not pre-marinaded). I thought I would cook it at 60 celsius but was unsure of length of time. I figure 24 hours would be the minimum and 48 might be too long - I don't want mushy, just pull apart texture. On searches, several people have used 68 celsius for 22 hrs for pulled pork, but that is a different beast. Any suggestions would be appreciated.

DocDougherty · June 8, 2011

I do tri tip at 59°C for 24 hrs and it comes out medium all the way through and fork tender, so I suspect that 60°C is a bit low. My next step up is 165°F for 24 hrs for turkey thighs but that is almost confit and probably too much. So 70°C for 24hrs might be a place to start. I will be interested in what others suggest.

Doc

KennethT · June 8, 2011

I typically do 62C for like 3 days for pulled pork - that's the most succulent I've ever made... I think it also matters what the fat content is of the meat - really lean pieces tend to dry out more...

dcarch · June 8, 2011

Regarding corrosion:

Anytime you have an alternating magnetic field near a conductive material, electric current will be generated.

If you have a 1,000 watt heater in the bath, a lot of electric current could be circulating in the metal components. This can set up an electro plating situation and metals can be corroded.

Just a theory.

dcarch

dougal · June 8, 2011

Regarding corrosion:
Anytime you have an alternating magnetic field near a conductive material, electric current will be generated.
If you have a 1,000 watt heater in the bath, a lot of electric current could be circulating in the metal components. This can set up an electro plating situation and metals can be corroded.
Just a theory.

Whatever it is that you are smoking, its not good for you.

Read this instead - (from the British Stainless Steel Asssociation) - http://www.bssa.org.uk/topics.php?article=89

No need for new theories.

Aluminium in contact with a 'large' area of stainless steel, and a conductive liquid, will result in the Aluminium corroding.

A large area of 'cathode' relative to 'anode' will accelerate the anodic corrosion. Although aluminium is anodic to stainless steel, large relative surface areas of aluminium to stainless steel can be acceptable, dependant on local conditions.
Stainless steel fasteners in aluminium plates or sheets are normally considered safe, whereas aluminium rivets or bolts holding stainless steel parts together is an unwise combination, as there is a practical risk of corrosion.

OliverB · June 8, 2011

that's odd, I just looked at my Demi, there's no corrosion at all. Once the water is cool I always empty it out and once dry I put the machine away, but seems like you do the same. I guess one could get some silicone tubing, cut into 1 inch or so pieces, slice open and snap around the stainless steel parts, but it seems really odd to me that this corrosion would happen so fast. And you say it's in the tank itself as well? Mine is painted with what looks like non stick coating (but may be anything else) and has no markings. I am careful with the aluminum part though, it has sharp corners that I'm afraid can scratch through the coating of the Demi, I might sand them down some day.

dcarch · June 8, 2011

Regarding corrosion:
Anytime you have an alternating magnetic field near a conductive material, electric current will be generated.
If you have a 1,000 watt heater in the bath, a lot of electric current could be circulating in the metal components. This can set up an electro plating situation and metals can be corroded.
Just a theory.
Whatever it is that you are smoking, its not good for you.
Read this instead - (from the British Stainless Steel Asssociation) - http://www.bssa.org.uk/topics.php?article=89
No need for new theories.
Aluminium in contact with a 'large' area of stainless steel, and a conductive liquid, will result in the Aluminium corroding.
A large area of 'cathode' relative to 'anode' will accelerate the anodic corrosion. Although aluminium is anodic to stainless steel, large relative surface areas of aluminium to stainless steel can be acceptable, dependant on local conditions.
Stainless steel fasteners in aluminium plates or sheets are normally considered safe, whereas aluminium rivets or bolts holding stainless steel parts together is an unwise combination, as there is a practical risk of corrosion.

In the absence of a final proven determination of the cause of the situation, it may not be a good idea to use one theory to rule out all the others, no matter how unlikely. The tranformer effect and electro plating effects are just possiblities. I am fully aware of the possible interaction between aluminum, aluminum alloys and the numerous stainless steel compositions.

Whatever I am smoking apparently is not the same as what you have been inhaling.

dcarch

**paulpegg** · June 8, 2011

My solution would be to avoid using the stainless steel rack. End of problem.

e_monster · June 8, 2011

I did some burgers at 145 F today (~63C). Can anybody explain why they came out totally gray, with no hint of pink?
Follow-up: I recently calibrated the sensor using boiling water (I figure, as a standard, it's closer to cooking temps than ice water is), and my sensor was under-reading by about 2.3F. Huge deal? Maybe.
I'll have to do more to see.
Inaccuracy of 2.3°F/1.3°C is not quite what we desire. If you do not have an ISO- or NIST-calibrated reference thermometer, you might calibrate your sensor or thermometer in ice-water (no need for distilled water, tap water will do, molecular freezing point depression in tap water is neglectable for our purposes) and in boiling water (taking into account altitude above sea level and barometric pressure; a difference of 40 mBar makes a 1°C difference) and against an ovulation thermometer at 100°F/37.8°C. With temperature stability of ±0.1°C in a PID-controlled water bath (SousVideMagic or immersion circulator) inaccuracy of more than 0.2°C is absurd.
See the Wikia article Importance of temperature control on pasteurizing times (0.5°C inaccuracy makes a significant difference in pasteurizing times) and the Wikia article on thermometer calibration: sensors and thermometers are not guaranteed to be linear and equally accurate over the whole range from 0°C to 100°C; 50k thermistors (SVM 1500C and 1500D) are better than 5k thermistors (SVM or Auber 1500A and 1500B).
See also the sous vide page in wikiGullet (the sum of accuracy and stability should be ±0.25°C or better for long-time cooking and pasteurizing).

I think that it is worth noting that because of the non-linearity that -- depending on the unit -- calibrating with boiling water may be significantly less useful than calibrating to an ovulation or fever thermometer. On my Auber units, I have been told that the response is pretty flat from about 80F to about 150F but that between 150F and boiling there is a loss of accuracy so that calibrating to boiling water could introduce a few degrees of error. It is my understanding that there is more drift from 150F to boiling than there is from 32F to 150F.

Best,

Edward

PedroG · June 8, 2011

Sure looks like galvanic corrosion. Try a marine outfitter (e.g., West Marine) for a zinc anode. Changing the water in the tank might help some too.
The vendor could put in a back-bias that counteracts the corrosion potential, but probably won't.
I don't generally store water in the tank when it's not in use, so changing the water wouldn't help. The tap water here is very hard (25 gpg or ~430 ppm), but softened with an ion exchange unit. If this is galvanic corrosion then wouldn't the stainless food rack be involved? It's been my impression that the worst spots on the grill are from where it is in contact with the rack, but it could be my imagination.

Does your ion exchange unit exchange only cations (Na⁺ for Ca⁺⁺ and Mg⁺⁺) or also anions? In the latter case, chloride ions may cause corrosion of aluminium.

mcdiarmid · June 9, 2011

I do tri tip at 59°C for 24 hrs and it comes out medium all the way through and fork tender, so I suspect that 60°C is a bit low. My next step up is 165°F for 24 hrs for turkey thighs but that is almost confit and probably too much. So 70°C for 24hrs might be a place to start. I will be interested in what others suggest.
Doc

I have just started a batch at 68˚C and will check at 24 and 48 hrs to test shredding. Elastic tissue should easily break down nicely at that temp and given that tenderness doesn't seem to improve above 70˚C (per baldwin's lit search), I think that will be my best bet. Will report back.

Phaz · June 9, 2011

How important is it that the entire bag is submerged? I barely fit two full pork shoulders (in 4 bags) into my SVS and for the most part they are in the water just fine, but two of the bags have maybe a 1/2 inch to inch of meat that just barely sticks out of the top of the water. I'm doing 150 degrees for 72 hours (as per MC).

I suspect with a cook that long it won't make too much of a difference, and the meat towards the top will still be roughly the temperature of the rest of it and everything will be fine, but does anyone have any experience with this? I might flip the bags every day just to be sure.

**nickrey** · June 9, 2011

How important is it that the entire bag is submerged? I barely fit two full pork shoulders (in 4 bags) into my SVS and for the most part they are in the water just fine, but two of the bags have maybe a 1/2 inch to inch of meat that just barely sticks out of the top of the water. I'm doing 150 degrees for 72 hours (as per MC).
I suspect with a cook that long it won't make too much of a difference, and the meat towards the top will still be roughly the temperature of the rest of it and everything will be fine, but does anyone have any experience with this? I might flip the bags every day just to be sure.

I'd be more worried about inaccuracy in the temperature within the cooker as you won't be getting any natural convection to circulate the water in the SVS.

dougal · June 9, 2011

How important is it that the entire bag is submerged? ...

It is IMPORTANT that the entire payload is submerged.

You are cooking IN water, to control the temperature. But OUT of the water, you simply don't have control.

Of course, it doesn't matter at all if any plastic 'above' the seal protrudes from the water.

My thinking is that everything below the seal needs to be assured food safe (so pasteurised for long cooking), and with fluid in the bag, I don't see how you can be absolutely confident of food safety in long cooking with any of the sealed space being out of the water.

And what nickrey said about permitting good water circulation all round each of your bags.

One nice aspect of sv is that you can interrupt the cooking, without necessary detriment.

So, I think you should immediately ice-water chill half your bags, and store them in the fridge as batch 2, while you finish cooking (and properly pasteurising) batch 1.

When batch 1 is cooked, chilled and stored away, batch 2 can have use of the bath to complete its cooking.

If you want to serve all the stuff as a single meal, it should then just be a matter of reheating both batches to serving temperature - which should not involve any question of pasteurisation and such - simply getting it to plating temperature anyhow you care to!

Edited June 9, 2011 by dougal (log)

dcarch · June 9, 2011

"-----but two of the bags have maybe a 1/2 inch to inch of meat that just barely sticks out of the top of the water. I'm doing 150 degrees for 72 hours (as per MC).------"

If your cooker has a cover, all you have to do is to measure the air temperature inside the cooker. It may be not too far from 150 degrees. If that is the case, by convection and conduction, the meat above the water will be very OK, not ideal, but OK.

However, specific heat of air is not as much as water, you will need to turn the meat around to submerge frequently when you first start so that you can get the meat up to temperature quickly.

dcarch

Edited June 9, 2011 by dcarch (log)

PedroG · June 9, 2011

Thermometer calibration

Pedro's point is a good one.
But I do wonder if we can achieve accuracy within ±0.25C unless we all have expensive ISO- or NIST- calibrated thermometers, which clearly most of us do not have.
Unless you can absolutely guarantee the accuracy of your set up, it is extremely inadvisable to play around at the lower limits of sous vide temperature for long cooking times. After our discussion on this forum, I believe this is why Merredith went to a much more accurate, and expensive, setup than her Sous Vide Supreme.
It is better to add a few degrees on to the temperature and to extend the cooking time to incorporate a margin of error than to risk the health of either you or your customers. If you want to work on the edge, make sure you are appropriately equipped to do so, including having all equipment in the process calibrated and functioning within a ±0.25C error rate.

I think that it is worth noting that because of the non-linearity that -- depending on the unit -- calibrating with boiling water may be significantly less useful than calibrating to an ovulation or fever thermometer. On my Auber units, I have been told that the response is pretty flat from about 80F to about 150F but that between 150F and boiling there is a loss of accuracy so that calibrating to boiling water could introduce a few degrees of error. It is my understanding that there is more drift from 150F to boiling than there is from 32F to 150F.
Best,
Edward

As it would be best to have a calibrated reference thermometer instead of trying to calibrate at 0°C/37°C/100°C, I started compiling a market overview of precision thermometers in wikiGullet. Please contribute your experiences and criticisms and ideas.

Phaz · June 9, 2011

"-----but two of the bags have maybe a 1/2 inch to inch of meat that just barely sticks out of the top of the water. I'm doing 150 degrees for 72 hours (as per MC).------"
If your cooker has a cover, all you have to do is to measure the air temperature inside the cooker. It may be not too far from 150 degrees. If that is the case, by convection and conduction, the meat above the water will be very OK, not ideal, but OK.
However, specific heat of air is not as much as water, you will need to turn the meat around to submerge frequently when you first start so that you can get the meat up to temperature quickly.
dcarch

Thanks for the tips (Thanks to the others as well).

Yeah, that's what I was thinking. I also thought that it would be pretty close to temperature since meat itself is mostly water (as MC is fond of telling us) and if the meat just below the surface is hot enough it seems like the meat just above the surface would be about the same temp, minus a tiny bit. Before I left for work I grabbed that meat through the bag and could tell it was certainly hotter than 140. I think when I'll get home I'll pull it out and probe it and see how it compares to the rest.

One nice thing is that with the meat getting a little softer it's settled a bit so now almost all of it is submerged.

I knew with all the crowding that the temperature wouldn't be very normalized through things. There's enough water in the gaps that it should be within a few degrees of each other, but I'm ok with that. With a 72 hour cook like this I'm not to worried about a little variation. I don't think the difference between 147 and 153 would be something I'll notice.

It does make me realize that the SVS is a little limited. I want to do a BBQ this summer for about 50 people using MC's techniques for all the meat, unless I started a few weeks in advance and did everything in batches then threw it in the fridge/freezer I don't see that working with the SVS. Maybe it's time to look at one of the circulators...

e_monster · June 9, 2011

"-----but two of the bags have maybe a 1/2 inch to inch of meat that just barely sticks out of the top of the water. I'm doing 150 degrees for 72 hours (as per MC).------"
If your cooker has a cover, all you have to do is to measure the air temperature inside the cooker. It may be not too far from 150 degrees. If that is the case, by convection and conduction, the meat above the water will be very OK, not ideal, but OK.
However, specific heat of air is not as much as water, you will need to turn the meat around to submerge frequently when you first start so that you can get the meat up to temperature quickly.
dcarch

If you are trying to be food safe and are using the tables that various people have produced and shared rather than directly measuring the temperature of the meat that is above the water, knowing the air temperature in the air cavity above the water doesn't help you that much as the heat conductivity of air is radically lower than that of water. All of our sv tables about time to emp are based on the time that it takes a piece of meat to get to a safe temp and the calculations assume that it is immersed in water. Food cooked in 150F water gets close to 150F MUCH faster than food cooked in 150F air.

**paulpegg** · June 9, 2011

I knew with all the crowding that the temperature wouldn't be very normalized through things. There's enough water in the gaps that it should be within a few degrees of each other, but I'm ok with that. With a 72 hour cook like this I'm not to worried about a little variation. I don't think the difference between 147 and 153 would be something I'll notice.
It does make me realize that the SVS is a little limited. I want to do a BBQ this summer for about 50 people using MC's techniques for all the meat, unless I started a few weeks in advance and did everything in batches then threw it in the fridge/freezer I don't see that working with the SVS. Maybe it's time to look at one of the circulators...

You can always build a beer cooler unit such as this http://egullet.org/p1777037 . If you read the article I referenced at Les Marmitons NJ you will see the larger version. I recently upgraded the pump to an external centrifugal pump with the ability to withstand up to 105C. The original pump didn't like 83.9C! I m still under $200 for this unit and use it every day. The beer cooler will easily accommodate meat or vegetables for 50 people or more. I used it for a vegetable course for 150 people in November.

I found that some bags would float to the surface, so I purchased some stainless steel pipe nipples and roll them up in the top of the sealed bag and clamp the bag on the ends with office paper clamps to keep them from sliding out. They hold everything close to the bottom and nothing floats. I tried aluminum plates at first and found that they corroded and I didn't care for the way they looked so I tossed them.

rotuts · June 9, 2011

eventually, moving to a beer-cooler and an air bubbler makes a very big difference in terms of energy usage, and amounts one can do at one time.

but the real point is to get SV-ing !

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