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View Full Version : Question about low temp cooking (sous vide, slow roast, etc.) and safety



heirkb
08-18-2013, 01:03 PM
Can someone link me to a site that explains safety issues with low temp cooking? The main thing I'm confused about is why so many people seem scared of very slow roasting if sous vide has been established as safe. What would make cooking in a 165-200 oven different from cooking sous vide? Is it an issue with the efficiency of air vs water when it comes to transferring heat into the food? Even if that's a concern, isn't what makes sous vide safe the length of time the food is kept at that lower temperature (as opposed to 20 minutes at 500 degrees farenheit, for example)? I remember reading something Heston wrote about this I think a couple years ago where he linked to a scientific paper that actually studied this very issue. Can't find it now...

gic
08-18-2013, 01:15 PM
as I mentioned in a previous thread. The following is the current definitive word:

http://www.fsis.usda.gov/OPPDE/rdad/FSISNotices/RTE_Poultry_Tables.pdf

Since then I have also found this (very technical) report on fish , also from the USDA, alas this oen doens't have a simple table to read information off of, although Table 7 is helpful

http://www.fsis.usda.gov/wps/wcm/connect/de34121e-cdaf-4d2a-9f9d-1976926e1715/NACMCF_JFP_Manuscript_07-612R.pdf?MOD=AJPERES

heirkb
08-18-2013, 04:25 PM
So it seems that most of the info in the links is about only one or two specific bacterial concerns. The concern a lot of people cite is that bacteria will grow in the food in such a low-temp cooking procedure, because it takes so long to raise the internal temp. Would the findings about time/temperature for the bacteria mentioned in these studies be generalizable for other concerns as well? I guess they must be if sous vide is considered safe and restaurants can use it, but I wanted to see a source on it and also a source on cooking the same way in the oven if there is one.

wellminded1
08-18-2013, 05:41 PM
This is a good resource I found a few years back, hope it helps you somewhat,
http://www.cookingissues.com/primers/sous-vide/

heirkb
08-18-2013, 09:28 PM
This is a good resource I found a few years back, hope it helps you somewhat,
http://www.cookingissues.com/primers/sous-vide/

Thanks for the link. It was definitely interesting. The thing with them, though, is that they claim that low-temp cooking requires a medium more efficient than dry air. That returns me to my initial question, then, which is if it's possible to cook at let's say 165-200F in an oven as long as the interior of the product has been at a certain temperature for a certain length of time. Basically, is there a good case against that kind of super low and slow roasting or not?

wellminded1
08-18-2013, 09:36 PM
Personally I do not see anything wrong wit roasting at this temp as long as you finish with a high heat and your core temperature reaches the desired goal. Another thing you have to remember is that sous vide, you usually vac pac, which draws out most of the air, which we know is a contributing factor to bacteria growth.

mckemaus
08-19-2013, 02:22 PM
Sous vide, by definition, is done with ingredient sealed in a bag, i. e. in an anaerobic environment. Many of anaerobic bacteria are nastier than the aerobic one, like Clostridum Botulinum, the bacteria that cause botulism, being one.

One of advantage using water bath is it is easy to know and to maintain the precise temperature of the bath, compared to ambient temperature and amount energy transferred in a low temp oven.

Mucho Bocho
08-19-2013, 02:31 PM
Len, People have been doing low temp cooking since we discovered fire. Think about Crock Pots (Pots of Crock is what I call them). Anyhoo, The main difference between 140 degree air and 140 degree water. Its all about Heat capacity and specific heat. Here is a link with a pretty good diagram. Basically think about how much energy is needed to heat water, we'll water is holding onto the heat and transferrs very efficently to our foods.

Think about putting your hand in a 200 degree oven. now think (don't try) what would happen to your hand if you put it into 200 degree water.


http://www.usc.edu/org/cosee-west/Jan292011/Heat%20Capacity%20and%20Specific%20Heat.pdf

Stumblinman
08-19-2013, 03:10 PM
While reading the USDA one it started to make no sense at all to me. Regarding table 7 they have temperatures listed but they seem to be calculated ones because in their experiments they never achieve those temps. It reads more like they're looking for the best medium to grow Listeria on. Blended crab meat shot up with Listeria then set to 99 degrees for two days...... I have a feeling it would be very hard to get past the smell and texture to even have the slightest thought on trying to eat it.

heirkb
08-19-2013, 03:50 PM
Len, People have been doing low temp cooking since we discovered fire. Think about Crock Pots (Pots of Crock is what I call them). Anyhoo, The main difference between 140 degree air and 140 degree water. Its all about Heat capacity and specific heat. Here is a link with a pretty good diagram. Basically think about how much energy is needed to heat water, we'll water is holding onto the heat and transferrs very efficently to our foods.

Think about putting your hand in a 200 degree oven. now think (don't try) what would happen to your hand if you put it into 200 degree water.


http://www.usc.edu/org/cosee-west/Jan292011/Heat%20Capacity%20and%20Specific%20Heat.pdf

So that's what I initially thought, but there are all of these recipes by Heston Blumenthal where he roasts in a super low oven. His roast chicken as well as his prime rib recipes both do that. Any word on safety there?

Mucho Bocho
08-19-2013, 04:03 PM
I do that with Chickena nd Prime Rib too, but they usually either start with high heat, then decrease or start on low then sear to get maillard after.

IN Modernist Cuisine, Nathan suggests putting a frozen steak in a screaming castiron pan, five minutes on side, then remove from castiron to another baking sheet and cooking it in a 200 degree oven for an hour hours. Comes out Medium Rare.

It is a little disapointing that these steaks in the demo aren't frozen. DUH

http://www.nytimes.com/video/2012/01/17/dining/100000001264267/in-the-kitchen-with-nathan-myhrvold.html

heirkb
08-19-2013, 04:22 PM
I do that with Chickena nd Prime Rib too, but they usually either start with high heat, then decrease or start on low then sear to get maillard after.

So since there is less energy in dry air, does that mean it'll just take longer but is no less safe than sous vide? (Sorry if that's a bad oversimplification, been a while since I took chem and physics courses). That's assuming that the meat stays at a certain combo of temp/time to insure safety (e.g. 15 minutes at 140F or whatever like that)

Also: That video/technique confirmed my personal suspicion of the desire to temper meat at room temp. I know that the guys at Serious Eats did a whole thing on how negligible the effect of tempering actually is in terms of temperature (i.e. the food doesn't actually get much warmer sitting out), but I always thought that it was silly to warm the inside of something when I want it to stay relatively cool while developing a nice crust.

Zwiefel
08-19-2013, 11:17 PM
Len, People have been doing low temp cooking since we discovered fire. Think about Crock Pots (Pots of Crock is what I call them). Anyhoo, The main difference between 140 degree air and 140 degree water. Its all about Heat capacity and specific heat. Here is a link with a pretty good diagram. Basically think about how much energy is needed to heat water, we'll water is holding onto the heat and transferrs very efficently to our foods.

Think about putting your hand in a 200 degree oven. now think (don't try) what would happen to your hand if you put it into 200 degree water.


http://www.usc.edu/org/cosee-west/Jan292011/Heat%20Capacity%20and%20Specific%20Heat.pdf

Right on MB! This is also a good example of the difference between heat and temp.

gic
08-20-2013, 03:05 AM
The key I have found in home cooking isn't the tempering but the drying - the less mist teh exterior the better the maillard reaction, I sometime take a hair dryer to stuff in fact :- )

JCHine
08-22-2013, 06:22 AM
Yep drying does far more to improve browning. After a steak sous vide cook I often cool down then serve next day after standing on edge in the refrigerator to dry the surface out. With a pre heated cast iron or de buyer you can get a fantastic finish.

apicius9
08-22-2013, 06:41 AM
The key I have found in home cooking isn't the tempering but the drying - the less mist teh exterior the better the maillard reaction, I sometime take a hair dryer to stuff in fact :- )

That is the first convincing argument I have ever seen for a hair dryer :)

Stefan

gic
08-22-2013, 11:36 AM
And it is the only use i have ever made of a hair dryer in my entire life :- )

Alas, my SO does take it back from the kitchen from time to time though and she often forgets to bring it back to the kitchen after she is done :- )

Mucho Bocho
08-22-2013, 11:39 AM
Gic, thats a unique trick but sounds like a PIA. The Key to home cooking... thats a pretty large statement.

Why don't you just pat your products dry and leave them unwrapped in refrigerator (dehydrator) for a couple of hours? Agreed that you can't acheive Maillard without removing surface moisture.

gic
08-22-2013, 12:20 PM
Oh no I didn't say the hair dryer was the key, I said drying was the key :- ). I used to use paper towels in fact but i find after sous vide the liquid that forms makes the number of paper towels needed ridiculous and i don't want to put it in the fridge, I want to eat it now after it is done, teh hair dryer trick did that...

Also it's amusing to find a personal use for a hair dryer after owning them for 30 years and never using one, no?? I only had them them for the GF...

Zwiefel
08-22-2013, 11:29 PM
I always wrap my proteins in a towel for 15-30ish minutes to ensure a very dry surface for Maillard. I've gotten lots of questions about it over the years....but only about 3 people have tried it themselves and reported on it. Everyone else thinks I'm crazy...but then they say it tastes pretty good :)

JCHine
08-27-2013, 08:30 AM
I always wrap my proteins in a towel for 15-30ish minutes to ensure a very dry surface for Maillard. I've gotten lots of questions about it over the years....but only about 3 people have tried it themselves and reported on it.

Tried the towel trick; worked a treat.

scotchef38
08-27-2013, 09:13 AM
I always wrap my proteins in a towel for 15-30ish minutes to ensure a very dry surface for Maillard. I've gotten lots of questions about it over the years....but only about 3 people have tried it themselves and reported on it. Everyone else thinks I'm crazy...but then they say it tastes pretty good :)
A trick i have used for years is to store the portioned meats or seafood on those soaker pads that you get on the bottom of packaged meats.You have to buy in bulk but they cost less than a cent.It is particularly good on skin on seafood portions-store them with the skin on the pad and when you cook them you get really nice crispy skin.

Clarence
08-19-2014, 02:02 PM
I stick a thermometer into the thickest part of the meat to reassure myself.

Zwiefel
08-19-2014, 03:42 PM
Tried the towel trick; worked a treat.

I must have missed this last year, excellent! super easy, and I would guess most of us have quite a stack of towels lying around.


A trick i have used for years is to store the portioned meats or seafood on those soaker pads that you get on the bottom of packaged meats.You have to buy in bulk but they cost less than a cent.It is particularly good on skin on seafood portions-store them with the skin on the pad and when you cook them you get really nice crispy skin.

Interesting...wonder how this would compare to the towel.