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Anonymous Modernist 9078

[Modernist Cuisine] Sous Vide Cooking Safety: Times, Temperatures, Storage, and Reheating

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Hello,

I have been studying the first book in depth over the last few months and I have a few questions regarding the safety of cooking sous vide (as well as a few other issues).

Firstly I wanted to ask a couple of questions on the table on page 193-1 "Extended & Simplified 6.5D Salmonella Reduction Table";

This table is referring to the killing of salmonella in different meats. I wanted to know if using these time and temperatures for all farmed meats would successfully eliminate ALL pathogens that we need to be concerned with, thus rendering it "safe" to serve to a customer? You have also stated that the interior of meat, so long as it's not punctured, should be sterile. I got the impression that this is not the case for chicken, and that chicken needs to be cooked to the times listed in the table. So why would the interior of chicken be inherently different to other animals? Not that I would want to serve chicken raw, I am just curious as to why this would be different to searing the outside, and eating a raw interior, as you can with beef etc?

I understand that wild game is a little different, as you are more concerned with parasites and the like, which shall bring me on to my next question;

I have seen restaurants serving Venison carpaccio, and I would love to make a venison tartare, but would that be foolish considering this animal is classed as "Wild Game"? It is served raw all over the country, so I am interested to learn how this differs to farmed beef for e.g.?

Next, I would like to learn a little about the reheating or "regenerating" of meat. If, for e.g., I was cooking chicken sous vide, and I cooked it at 54ºC for 2h17m to achieve a 6.5D reduction, could I then chill in an ice bath and reheat it to order? In the UK, legislation states that cooked meats need to be reheated to 86ºC to be safe. Now obviously this would ruin a chicken. A restaurant that I know cooks Venison at 55ºC, chills it and then "regenerates" it at 50ºC to order. Is that safe? I am interested in cooking/reheating options.

And finally, the last question I have is regarding fish. Now I understand that if I cook fish to the time/temp listed in the chart on 193-1, I will likely result in fish that is overcooked to most peoples liking. However if I freeze it to the suitable time/temp, that renders it safe to serve raw, correct? Now using the current freezer I have, which sits at about -20ºC, I think that freezing in this way will be of detriment to the quality and texture of the flesh. Is that a fair comment? And how could I bypass this stage? Is that just a risk that restaurants take and, much like serving raw salad, occasionally someone might get sick from it?

Apologies for the length of this text, and I hope the questions I ask are interesting for you to answer.

I look forward to hearing back from you.

Thanks very much advance.

Iain sf-smile.gif

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I know that for absolute safety food should be cooked SV to achieve a particular internal temp within a certain time. However, I am generally not too concerned about that, especially for fish as pasteurised fish is way too cooked for my taste and I believe that the unexposed flesh on a thick fillet is unlikely to be dangerously pathogenic.

My main concern is to kill or greatly reduce any pathogens on the surface. So I'm wondering if putting my fish fillets into a SV bag, dunking the bag into 170-180F water for a few seconds and then putting it into the SV bath to achieve an internal temp of say, 119F, will provide sufficient safety.

Any thoughts?

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If you dont want to brown/burn the delicate flesh then dont use a blowtorch or other source of flame. But i would dunk in boiling water (212F) for 30 seconds should be enough to kill any surface bacteria without over cooking.

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You can use an app to help determine when the surface is pasteurized. I use SousVide Dash for iOS and it works rather well.

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Ozcook, you don't mention parasites. Hard freezing will solve that problem, see § 3‑402.11 of the FDA Food Code, but AFAIK heat is the only control for parasites that works with fresh fish (except tuna, which apparently doesn't get them). See Baldwin. Indeed, as I too don't care for the texture of sous vide pasteurized fish, I use sous vide only for previously hard-frozen (or tuna) and cook to very low temp (below pasteurization). Fresh I cook by conventional methods.

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I'm not sure if it's 100% relevant, but I found an interesting study on the use of hot water to sterilise knifes in abattoirs. I was actually trying to find any scientific studies on whether hot water could dull a sharp knife, but this one ended up being more interesting.

Commissioned by Australia's CSIRO, you can read the full article here.

Bearing in mind that the study was on bare metal knives, and not a plastic pouch of food, one line was quite poignant:

"Peel and Simmons (1978) showed that momentary immersion of knives at 82°C, on its own, was ineffective in decontaminating knives of Salmonella. When fats or proteins are present on them, immersion of knives at 82oC for as long as 10 s will not give satisfactory reduction in bacterial contamination (Snidjers et al., 1985)."

So if you are going to use hot water immersion to pasteurise the surface of vacuum bagged food, ensure the water temperature is well over 82C and you immerse it for longer than 10 seconds.

Perhaps those who are more knowledgeable on these topics will be able to judge if that study has any relevance to sous vide.

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Very interesting question. My strategy for low temperature delicate items which I don't want to sear, like fish or seafood, is to fast freeze for parasites (or buy frozen) and vacuum seal. Then I cook from frozen (to 45-50ºC internal temperature) and dunk into boiling water for about 10-20 seconds. I don't dunk first because it is cooked from frozen. Dunking at the end should require less time as the surface is at a higher temperature, and also helps the portions not to feel so cold. I've done comparisons side-to-side between pieces dunked and not dunked and the difference is hardly noticeable.

But I don't have a rigorous support of the safety of this strategy.

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Very interesting question. My strategy for low temperature delicate items which I don't want to sear, like fish or seafood, is to fast freeze for parasites (or buy frozen) and vacuum seal. Then I cook from frozen (to 45-50ºC internal temperature) and dunk into boiling water for about 10-20 seconds. I don't dunk first because it is cooked from frozen. Dunking at the end should require less time as the surface is at a higher temperature, and also helps the portions not to feel so cold. I've done comparisons side-to-side between pieces dunked and not dunked and the difference is hardly noticeable.

But I don't have a rigorous support of the safety of this strategy.

The reason for higher temps on the surface first is so that you kill any bacteria that could likely grow while cooking. In your case, if there was any bacteria it would have most likely penetrated into the fish. Depending on the temp you cooked, dunking after would be pointless. However, if you were to quickly dunk in boiling water first, then cook at a low temp like 127F, then your chances of bacteria growing will be reduced.

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The reason for higher temps on the surface first is so that you kill any bacteria that could likely grow while cooking. In your case, if there was any bacteria it would have most likely penetrated into the fish. Depending on the temp you cooked, dunking after would be pointless. However, if you were to quickly dunk in boiling water first, then cook at a low temp like 127F, then your chances of bacteria growing will be reduced.

That was my thinking too. I want to kill, or greatly reduce, surface bacteria before freezing. The replies above are very interesting. My reading of the knife study is that either method will work and that the lower temp is better from an occupational safety viewpoint. As that is not an issue for me, my current conclusion is that a 10 second dunk in 85c water should provide reasonable protection. However I am certainly open to further information.

Thanks.

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Ozcook: With respect, I think you're missing the point of the study linked by ChrisZ. (Which, I will say, was news to me.) The standard assumption, and the one underlying your OP, is that brief cooking at high temp kills substantially all bacteria. See, e.g.,, the American FSIS tables for cooking beef and poultry. The linked study suggests this assumption is overly optimistic. Now, it may be that the real lesson to be learned here is that the effectiveness of brief-high-temp depends on the bacterial load (most failures in the study came early in the slaughter process), but knives vs. meat isn't the issue. BTW, I notice you skipped over the parasites problem.

FeChef: If bacteria can migrate into the interior of sous vide fish, the whole premise of the OP and my own practices with respect to previously frozen are suspect. (Surely you don't assume the bacteria can only migrate at moderate temps) Do you have a cite?

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Very interesting question. My strategy for low temperature delicate items which I don't want to sear, like fish or seafood, is to fast freeze for parasites (or buy frozen) and vacuum seal. Then I cook from frozen (to 45-50ºC internal temperature) and dunk into boiling water for about 10-20 seconds. I don't dunk first because it is cooked from frozen. Dunking at the end should require less time as the surface is at a higher temperature, and also helps the portions not to feel so cold. I've done comparisons side-to-side between pieces dunked and not dunked and the difference is hardly noticeable.

But I don't have a rigorous support of the safety of this strategy.

The reason for higher temps on the surface first is so that you kill any bacteria that could likely grow while cooking. In your case, if there was any bacteria it would have most likely penetrated into the fish. Depending on the temp you cooked, dunking after would be pointless. However, if you were to quickly dunk in boiling water first, then cook at a low temp like 127F, then your chances of bacteria growing will be reduced.

Do you have any support for these claims? Whereas I dunk first when I am not cooking from frozen, I don't see that much difference between both strategies. Yes, existing bacteria could grow during the cooking period, but not that much, as we are talking here about delicate items with fast cooking times, between 10 and 30 minutes. On the other hand, dunking after cooking should allow a shorter dunk time, as getting the surface to around 80ºC is much faster when the food surface is at 45ºC that when it is at 5ºC.

The claim that bacteria would penetrate the fish is contrary to most safety documents I've read. Muscle interior is generally assumed to be sterile, except for parasites. That's why it's safe to eat meat that has been fast seared while keeping the interior at non-pasteurized temperatures.

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Greetings, I have a few large slabs of chuck roast, ~2" and a bit of a safety concern. One side of the roast is having water at 138 f circulating around it while the other side is pretty much pressed against the wall of the tank. Is this a safety concern or more of an uneven cooking problem? Using the Anova circulator in about 4 gl water filled plastic tank for about 48 hours.

 

New to this delicious cooking method, my other meals have turned out wonderfully. Just don't want to get anyone sick.

 

Thanks for any help :)

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I did a chuck at 137f/27hr. Sliced for roast beef sandwiches. Was med/rare with good texture

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You might want to suspend the bag in the center of the vessel.

A binder clip, string and a chopstick work great

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as I under stand it :  you are using the Anova, and some of your bags are being pushed 'aside'

 

Id  do this;  from time to time, say every 20 - 30  min, just give the bath a swish.  move the bags around.

 

this until the bags reach the target temp.

 

id this does not seem to work

 

look for a 'rib rack'  they are stainless steel and at all the major places   Home depot etc

 

http://www.homedepot.com/s/rib%2520rack?NCNI-5

 

like this..  every other.

 

once you become a true student of SV  you will move to 'Beer Coolers'  which mitigate some of these issues.

 

Bon Appetite 

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your system aside, based on it size and volume,

 

you might consider and aquarium pump :

 

http://www.amazon.com/s/?ie=UTF8&keywords=pumps+for+aquariums&tag=googhydr-20&index=pets&hvadid=27022004523&hvpos=1t1&hvexid=&hvnetw=g&hvrand=7374966957703200684&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_q28x2n94f_b

 

less than 10 bucks is all you need   some flexible tubing and an 'aquarium stone'

 

http://www.amazon.com/Jardin-Aquarium-Ceramic-Diffusers-Diameter/dp/B0050HJ7Q6

 

it bubble at the far end of your set up and moves the water around for even heating.

 

I use them.  but have not prgressed to the Anova  'yet"

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FWIW, I raised a similar concern a few days ago in the Anova thread.  JoNorvelleWalker posted that she has tested between clumped bags and found the water stays at the set temp.  Meanwhile, in another thread, KennethT reports that he tested temp below bags resting on the bottom of a water bath and again found no problem.  In other words, it seems we're making much ado about nothing.  Circulation and the naturally efficient heat transfer of water does the trick.  If you want to be absolutely certain, put a flat rack in the bottom of the bath and use a vertical rack or other procedure (e.g., the one gfweb suggests) to keep the bags separated and away from the sides.  I do this because I can, easily, but it isn't necessary and isn't standard practice in commercial kitchens.

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At one point a few years ago, I tested my circulator's water circulating ability by putting a bunch of bags in the bath and then putting a few drops of food coloring in the corner (away from the bags). In a matter of seconds, there was food coloring everywhere - even between the bags that were pretty closely packed together. I did this in several trials and found the same results each time.

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nice work  

 

what was your set up ?

 

PedroG did this a long time ago and had some Vids.

 

SVMagic I think it was.  the circular item w the large bubbler.

 

again, nice work

 

the Anova crowd might do this and cap that discussion.

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My circulators are home made. I'm a manufacturer of non-food related products, and a few years ago, was entertaining the idea of making circulators for SV. So I made prototypes for testing and de-bugging. I don't want to get too much into the details, but our design is very different from the types currently on the market as the device does not go into the cooking chamber, which leaves more room for bags. With that being said, my circulation isn't as strong as some of the immersion circulators, which is why I felt it necessary to do circulation tests.

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My circulators are home made. I'm a manufacturer of non-food related products, and a few years ago, was entertaining the idea of making circulators for SV. So I made prototypes for testing and de-bugging. I don't want to get too much into the details, but our design is very different from the types currently on the market as the device does not go into the cooking chamber, which leaves more room for bags. With that being said, my circulation isn't as strong as some of the immersion circulators, which is why I felt it necessary to do circulation tests.

 

I think I have an idea the thinking behind your device. But I will not disclose the idea, since you want to have a marketing advantage.

 

It is a clever way to make SV appliance better. Clean, and less maintenance.  You should definitely market it.

 

dcarch

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Host's note: This topic was split from the Dinner 2014 (Part 5) topic.

Rotuts -- 144. I actually did a whole piece, which is going to be dinner tonight....

72 hours at 54C (130F) is absolutely incredible. Currently doing that now. A bag might have leaked, but I'm letting them go and see how it turns out.

Check this out - http://www.chefsteps.com/activities/short-ribs-time-and-temp


Edited by Smithy (log)

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