Sous Vide: Recipes, Techniques & Equipment, 2011

[blackp]

The vacuum level dilemma with chamber sealers for sous vide cooking

Edge sealers suck all air out of the bag before sealing, tightly fitting the bag to the food; so even with low vacuum levels, there is virtually no air left in the bag, except for some surface irregularities of the food to which the plastic may not have been snugly fitted. Maximum vacuum levels achieved by edge sealers (80-90%) will not damage food by cold boiling and/or compression (see Dave Arnold's "Boring but useful technical post: vacuum machines affect the texture of your meat" and Modernist Cuisine page 2•213 "Boiling not Crushing").

In contrast, chamber sealers suck the air out of the bag and its surrounding, then seal, and the bag will only be fitted tightly to the food after releasing the vacuum from the chamber. To fit the bag snugly to the food, vacuum levels of 99% to 99.9% are applied. These vacuum levels may damage delicate food like fish or poultry. Reducing the vacuum level in a chamber sealer to e.g. 80% may leave some air in the bag causing floating and poor heat transmission: if the initial air volume between food and bag was e.g. 200ml, after sealing in an 80% vacuum there will be 40ml of air (that’s a jigger!) left in the bag.

If there is no edge sealer at hand for sealing delicate food, a Ziploc bag may be preferable to the chamber sealer.

A way out with a chamber sealer might be using a sealed bag of water to weigh down the bag to be sealed and eventually a second sealed bag of water below the bag to be sealed, thus displacing as much air as possible out of the bag before sealing.

Pedro sent me this observation a few days ago and I checked his theory and can confirm it is correct. I had a chamber machine for some years before embarking on SV cookery, but had always used 99%+5sec. vacuum (or similar) for hard items and around 97% vacuum for softer products, based on my experience using the machine for freezing.

I had never even tried 80% vacuum for SV but prompted by Pedro I did and can confirm that items packed at even 90% vacuum will float in a water bath. With my machine settings of 95% or higher will remove enough air from the bag to allow it to sink without any help from weights or other devices. Note that my machine has a vacuum sensor to determine the level of vacuum rather than a timer which is used in some machines.

Dave Arnold from FCI published an article a while back (cited above in Pedro's post) which shows different results from bagging at different vacuum levels. In a recent dialogue Dave observed that even items vacuum packed to high levels and then re-packed into low pressure bags did not exhibit the same impact as those vacuumed to the same level and cooked in that bag.

Nathanm et. al. in Modernist Cuisine (2.213) suggests that the strong vacuum causes boiling which damages cells close to the surface of the food which subsequently causes liquid to leech from the item and alters the texture.

With that as background I wanted to see if there was any discernible difference in a food product vacuumed at a level which would allow the surface of the item to boil vs one which was not. I also wanted to see if re-packing an item originally vacuumed at a level where the surface would boil and then re-packing at a lower pressure would have any impact.

So this is what I did:

I used 3 nearly identical chunks of chicken breast each cut from the same breast. Each piece was 50g.

I bagged 2 at 99%+30sec and the third at 80%.

I opened then re-bagged one of the 99% pieces at 80%.

For the 2 pieces at 80% I added some glass marbles to the bag to make them sink.

The 3 samples were cooked at 60°C for 1 hour then chilled in an ice bath.

I unpacked each sample, dried them off and weighed them. There was no appreciable difference in weight - my kitchen scale only has 1g resolution so if there was a change it was less than that.

I cut each piece through the middle to see if there was any noticeable difference in texture and could not detect any. I did photograph the results but the photo doesn't show anything useful.

I cut a small slice from the middle of each sample and tasted it. Both the flavour and texture were identical - or at least close enough that my palate could not discern any difference.

So what I've learned is that (at least for chicken breasts) you can vacuum to any pressure with impunity.

As for Dave Arnold's observations all I can say is that things must be different in the northern hemisphere compared to here in the Antipodes! We know that water swirls down the drain in the opposite direction so what else is different?

Cheers,

Peter.

(Edited because I forgot to reference Modernist Cuisine)

Edited April 29, 2011 by blackp (log)

[Paul Bacino]

Anyone know of a reasonable device, that can sense both the highs and lows of the water bath and will alarm you if your bath range goes outside a : for example .5 ( F ) degree window.

So if I would sous vide ribs for 36-48 hrs. I would like an alarm if the thermal circulator goes whacky?

I see in a previous thread, that a second device is recommended.. in helping monitor the high end.

Thanks Paul

[blackp]

Anyone know of a reasonable device, that can sense both the highs and lows of the water bath and will alarm you if your bath range goes outside a : for example .5 ( F ) degree window.

So if I would sous vide ribs for 36-48 hrs. I would like an alarm if the thermal circulator goes whacky?

I see in a previous thread, that a second device is recommended.. in helping monitor the high end.

Thanks Paul

I use a Sous Vide Magic to control my SV cookery. It allows the setting of high and low temperature alarms, although I'd be reluctant to attempt to set those to 0.5°F. If I did it would go off while it was coming up to temp and would go off again when I put my food in to cook.

You should run some experiments with your SV device to see how accurate it is using a trusted thermometer.

Once you know how your device behaves you can then trust it to work for you.

If you are trying for the perfect poached egg at 64.5°C you need to be sure that the temp is not drifting (especially higher), but that doesn't take more than an hour. For most long term cooking stability inside 1 or 2 degrees should be OK.

I often cook beef ribs for 48 hours and usually do that at 57°C which is low enough for them to still be a bit pink when done. If they were cooked at 57.5°C or 56.5°C I'm sure I wouldn't notice much difference.

My point is that subtle temperature differences seem to have less impact for long term cooking and are more important for things cooked briefly like eggs or fish.

Cheers,

Peter.

[PedroG]

Anyone know of a reasonable device, that can sense both the highs and lows of the water bath and will alarm you if your bath range goes outside a : for example .5 ( F ) degree window.

So if I would sous vide ribs for 36-48 hrs. I would like an alarm if the thermal circulator goes whacky?

I see in a previous thread, that a second device is recommended.. in helping monitor the high end.

Thanks Paul

See upthread

[pep.]

So now that I have my a Polyscience immersion circulator, I'm looking for some tips how to best use it. I've got 1.4 kg of "tough" beef (a cut called "Rieddeckel", which would be a part of what you call chuck, viz. https://ssl.wiesbauer-gourmet.at/wissenswertes/fleisch/fleischkunde/rind_aussen/index.php?ID=4996). I'd like to serve it on Sunday, so I've only got around 32 hours to prepare it. Should I brine it for an hour or two? Give it more than 56°C? Will 24 hours be enough or should I aim to get it in for most of the 32 hours? I've also got some asparagus which I'd like prepare sous-vide, but I could do that conventionally if the beef needs the time.

[Merridith]

So now that I have my a Polyscience immersion circulator, I'm looking for some tips how to best use it. I've got 1.4 kg of "tough" beef (a cut called "Rieddeckel", which would be a part of what you call chuck, viz. https://ssl.wiesbauer-gourmet.at/wissenswertes/fleisch/fleischkunde/rind_aussen/index.php?ID=4996). I'd like to serve it on Sunday, so I've only got around 32 hours to prepare it. Should I brine it for an hour or two? Give it more than 56°C? Will 24 hours be enough or should I aim to get it in for most of the 32 hours? I've also got some asparagus which I'd like prepare sous-vide, but I could do that conventionally if the beef needs the time.

I have an SVP which holds it heat extremely well - I have never seen it vary more than .5 C. So I cook my chuc at 54.5 for 24 hours. I put frozen cubes of strong stock and I rub the meat with seasoning - onion powder, paprika, herbs, salt, pepper, etc. Trim as much fat as you can before seasoning and bagging, by the way, because at that temp you don't get good fat for eating. Heat and strain the bag juices, caramelize what sticks to your pot with some minced shallot, deglaze with wine or cognac and then serve over the meat - amazingly delicious.

[pep.]

I have an SVP which holds it heat extremely well - I have never seen it vary more than .5 C. So I cook my chuc at 54.5 for 24 hours. I put frozen cubes of strong stock and I rub the meat with seasoning - onion powder, paprika, herbs, salt, pepper, etc. Trim as much fat as you can before seasoning and bagging, by the way, because at that temp you don't get good fat for eating. Heat and strain the bag juices, caramelize what sticks to your pot with some minced shallot, deglaze with wine or cognac and then serve over the meat - amazingly delicious.

So 24 hours is enough? As for the fat, I intend to brown it with a blowtorch before serving, shouldn't that be enough to render it somewhat?

Greetings,

Peter

[Chris Amirault]

Merridith's advice is good, I think -- but you'll find a big difference between 54C and 56C chuck cooked 24 or 36 or 48 hours. In my experience, her instructions will give you meat that still has a bit of bite, not fall-apart tenderness. You may find that you like it a bit more this way or that, and can adjust if you keep notes.

I dunno of that blowtorch idea is going to work very well, but that's just a guess. I always brown the meat before going into the SVS, which helps a bit with the fat I haven't trimmed.

[dougal]

Anyone know of a reasonable device, that can sense both the highs and lows of the water bath and will alarm you if your bath range goes outside a : for example .5 ( F ) degree window.

...

I see in a previous thread, that a second device is recommended.. in helping monitor the high end.

See upthread

Any second device gives a useful 'sanity check'.

While most PIDs will provide High and Low alarm outputs, the thing is that the alarms are depending on the same sensor, and same sensor-reading electronics as the controller is depending on.

To protect against problems in those areas, you need a second system.

And to see how the temperature in the bath might vary - away from the primary temperature probe, again you need a second measuring system.

For basic sanity checking (watchdog functionality) it doesn't have to be particularly accurate.

But you might perhaps be more interested in datalogging the temperature at other point(s) in the bath ...

I'd agree that for long cooking, brief variations (as when adding other stuff to the bath) are irrelevant.

But for short (timed to the minute) cooking (seafood? eggs?), you'd like fast recovery to the target temperature after loading the bath, with minimal overshoot.

Edited April 29, 2011 by dougal (log)

[pep.]

Merridith's advice is good, I think -- but you'll find a big difference between 54C and 56C chuck cooked 24 or 36 or 48 hours. In my experience, her instructions will give you meat that still has a bit of bite, not fall-apart tenderness. You may find that you like it a bit more this way or that, and can adjust if you keep notes.

Yes, a bit of bite would be better. Actually, the shorter cooking time suits me fine. That means I will have the sous-vide rig available for other stuff on sunday and I will just need to bring the beef up to temp for serving. Originally, I put them in at 55.0°C, but I reduced the temperature setting by a half degree after I read your post.

For bagging, I split the beef into two parts as I didn't trust my cooking vessel (a 9.0l IKEA stock pot) with the larger bag. I've ordered a 27.5l bath, but that's not arrived yet. I salted and spiced both pieces (Tasmanian pepper, some black pepper, a sprinkling of crushed mustard seeds and juniper berries) before bagging them. We'll see how it works out.

I dunno of that blowtorch idea is going to work very well, but that's just a guess. I always brown the meat before going into the SVS, which helps a bit with the fat I haven't trimmed.

I've read that browning before putting the meat into the bag doesn't give the nice flavor (although it worked fine with my improvised sous-vide attempt a few weeks ago). But I trimmed the fat (about 200g) and what's left should melt/get crisped with the torch.

[Chris Amirault]

Lots of opinions on the browning before/after approach. I'm a before guy, for reasons of taste, relative ease (to me, anyway), and probably utterly unjustifiable habit.

[Merridith]

Merridith's advice is good, I think -- but you'll find a big difference between 54C and 56C chuck cooked 24 or 36 or 48 hours. In my experience, her instructions will give you meat that still has a bit of bite, not fall-apart tenderness. You may find that you like it a bit more this way or that, and can adjust if you keep notes.

I dunno of that blowtorch idea is going to work very well, but that's just a guess. I always brown the meat before going into the SVS, which helps a bit with the fat I haven't trimmed.

Yes, I agree with Chris - the difference is in the bite, i.e. the way it chews and the mouthfeel, on a subtle level. I have done 48, 36 and 24 hours. Each are very tender but the shorter time chews/feels more like a tender steak. The longer chews/feels more like a stew but without the stringy texture. Of course, it ALWAYS depends on the quality of your product. (Most here know that I only eat grass-fed, direct from farmer, meat. Since I buy large amounts at a time, chuck essentially costs the same as rib-eye so I tend to treat them all the same.)

At either temp and time, you won't get fat for eating. Try your torch. I am loathe to hold the torch on the fat long enough to achieve something I want to eat because I am always afraid of overcooking my meat. So I just justify this by the saving of the calories. I would torch it anyway, for looks, but I cut it away on my plate for eating.

[JBailey]

I am a sear after advocate. My thought is searing before may crisp, but time in the bag will soften the exterior crisping done in the pre-sear.

As for fat, I have begun trimming as much exterior fat as is possible. My thought is the fat does not render as much as if the meat was cooked conventionally. Even with post searing or torching, I agree with comments that the fat does not have the taste or 'mouth feel' one is accustomed to experiencing. However, when the fat is trimmed before sealing, I do put it back into the bag to seal with the meat so if flavor is enhanced with fat even at lower sous vide temperatures, it is there.

[KennethT]

Lately, I've been taking a hunk of fat and meat trimmings and rendering/frying until nicely browned - I then add this to the meat in the bag, then I'll sear the meat post SV. I'm not a big fan of adding liquid to the bag in most cases because I feel that it steals flavor from the meat a la making stock... Rather, I'll drain the juices and follow nickrey's suggestion of coagulating the proteins then frying them (replicating the brown bits on the bottom of the pan) then deglaze and add back the rest of the juices/stock for the sauce. I find that the added fat/trimmings add depth of flavor to the meat. If I'm cooking for a long time, I'll do a quick blowtorch pre-sear to kill any surface bacteria, not for color, and then post-sear for flavor/crust.

Edited for a bit more clarity... I hope...

Edited April 29, 2011 by KennethT (log)

[Chris Amirault]

Sorry -- should have qualified:

For LTLT cooking of things like chuck, I'm thinking stew, daube, that approach, so I sear first. For steaks and other items that I just bring to temp, I sear them just before service.

[JBailey]

KennethT

Lately, I've been taking a hunk of fat and meat trimmings and rendering/frying until nicely browned - I then add this to the meat in the bag, then I'll sear the meat post SV.

Yes, I also try to sear or brown when I have the time. This does impart a good flavor in my opinion.

[Robert Jueneman]

Pedro sent me this observation a few days ago and I checked his theory and can confirm it is correct. I had a chamber machine for some years before embarking on SV cookery, but had always used 99%+5sec. vacuum (or similar) for hard items and around 97% vacuum for softer products, based on my experience using the machine for freezing.

I had never even tried 80% vacuum for SV but prompted by Pedro I did and can confirm that items packed at even 90% vacuum will float in a water bath. With my machine settings of 95% or higher will remove enough air from the bag to allow it to sink without any help from weights or other devices. Note that my machine has a vacuum sensor to determine the level of vacuum rather than a timer which is used in some machines.

Dave Arnold from FCI published an article a while back (cited above in Pedro's post) which shows different results from bagging at different vacuum levels. In a recent dialogue Dave observed that even items vacuum packed to high levels and then re-packed into low pressure bags did not exhibit the same impact as those vacuumed to the same level and cooked in that bag.

Nathanm et. al. in Modernist Cuisine (2.213) suggests that the strong vacuum causes boiling which damages cells close to the surface of the food which subsequently causes liquid to leech from the item and alters the texture.

With that as background I wanted to see if there was any discernible difference in a food product vacuumed at a level which would allow the surface of the item to boil vs one which was not. I also wanted to see if re-packing an item originally vacuumed at a level where the surface would boil and then re-packing at a lower pressure would have any impact.

So this is what I did:

I used 3 nearly identical chunks of chicken breast each cut from the same breast. Each piece was 50g.

I bagged 2 at 99%+30sec and the third at 80%.

I opened then re-bagged one of the 99% pieces at 80%.

For the 2 pieces at 80% I added some glass marbles to the bag to make them sink.

The 3 samples were cooked at 60°C for 1 hour then chilled in an ice bath.

I unpacked each sample, dried them off and weighed them. There was no appreciable difference in weight - my kitchen scale only has 1g resolution so if there was a change it was less than that.

I cut each piece through the middle to see if there was any noticeable difference in texture and could not detect any. I did photograph the results but the photo doesn't show anything useful.

I cut a small slice from the middle of each sample and tasted it. Both the flavour and texture were identical - or at least close enough that my palate could not discern any difference.

So what I've learned is that (at least for chicken breasts) you can vacuum to any pressure with impunity.

As for Dave Arnold's observations all I can say is that things must be different in the northern hemisphere compared to here in the Antipodes! We know that water swirls down the drain in the opposite direction so what else is different?

Cheers,

Peter.

PedroG, blackp, and I have been debating this issue extensively off-list over the last several weeks, and together we proposed an experiment along the lines above.

Unfortunately, I'm just returning from the hospital and am still recuperating from double pneumonia. The chicken I cooked a week ago is still in the fridge, but I think its value as an experiment is now dubious, so I intend to repeat it. And I will photograph the results at 5X to record any discernible results. Rather than using marbles, I intend to order some stainless steel film clips, of the type used for drying 35mm film back in the old days.

I completely respect blackp, Dave Arnold, and nathamn, and I can't account for the differences in their results, although I doubt that it is due to the Coriolis effect and the rotation of the water as it goes down the drain. (Now there's a term I haven't used in nearly 50 years, since getting my degree in physics!)

Instead, I accounted for Dave's findings, as well as those reported in MC, by thinking that there might have been some crevices in or around his chicken breast, especially if there there any rib meat (and bones) attached that might make it difficult for the chamber vacuum to completely seal the bag around the meat. As a result, there might still be a significant pressure differential that would continue to boil the meat juices as the food is coming up to temperature. Since a 99.9% vacuum is enough to make an ice water bath boil, there is absolutely no question that it would make the juices in the meat boil, at least on the edges.

However, last night I sealed some pork ribs in my MVS-31X, which I believe is the same machine Dave Arnold uses, and it seemed to a very nice job of sealing, even around the big ribs. So I'm beginning to question my assumption.

The only way I see to to resolve this issue is through more testing, by more people; including those with chamber vacuums, and those with edge sealers. I would suggest following blackp's protocol, above, although I might extend the time to 2 hours at 64C. Maybe it takes more than a hour for the juices to leach out.

Then once we can answer that question, we can go on to explore the vacuum variables involved in long term frozen storage-- hard vacuum vs. 90% vs. 80%; and then the even harder issue of whether to use modified atmospheric packaging (MAP), with either nitrogen or CO2. To that end, I'm probable going to add the gas port adapter to my MVS-31X, and start with a pure CO2 mixture. CO2 plus water yields carbonic acid, which might increase the Ph enough to provide a bacteriostatic benefit, as has been reported with chicken in industrial practice

Hopefully there will be a sufficient number of users on this list with the kind of high-end equipment required to do these tests, as it's now apparent that a single user's tests may not be conclusive, due to equipment parameters and god knows what else.

Bob

[Robert Jueneman]

Yesterday, Costco has some corn on the cob which came 8 to a pack. I am going to do several ears for dinner. Usually, I put in a knob of butter with some other seasonings, seal them and drop them directly into my SVS or SVP at 185F. The other ears I was going to merely seal up to prolong their freshness for another meal. However, that got me to wondering. If I were to prep all the ears and seal them, could I do some for the table today and the others put back in the refrigerator uncooked then putting a pack in the sous vide later? What would happen if I seal them with my butter and spices and they were not cooked for two or three days? Does this cause a safety issue or would the ingredients become too strong in the corn? Would you sous vide all ears now and cool them down, refrigerate them and then pop them back in the sous vide to bring back to temp?

Maybe another way to ask the question, other than for marination, but rather for convenience what vegetables and meats can you season, hold and sous vide at another time?

I've tried corn on the cob SV, but to me, the long cooking time (1 hours at 85C) tends to make the corm taste too "cobby" for my taste. Nathanm, Thomas Keller, and others recommend slicing the kernels off of the cob, and cooking them with butter and other spices as desired -- perhaps my favorite, a little chipotle and lime.

Of course the dining experience is quite different, and if you don't have two SV machines, a little awkward in terms of preparation and holding times.

[Robert Jueneman]

Lots of opinions on the browning before/after approach. I'm a before guy, for reasons of taste, relative ease (to me, anyway), and probably utterly unjustifiable habit.

My recommendation would be to sear briefly before hand, if you are going to Jaccard the meat for additional tenderness, as I often do. This kills any bacteria that might be on the surface, before the Jaccard needles drive them below the surface.

Otherwise, I like the idea of slicing off some of the fat and other odd shaped bits, browning those in a pan, than adding it back to the bag with the meat. If you are cooking the steak, say, to a temperature that doesn't pasteurize the meat, like a rare 120F, I would briefly immerse the bag in boiling water (not necessarily in the SV apparatus) for say 15 seconds, and then SV at 120F, or 131F if you are serving someone with a potentially compromised immune system.

When it is cooked, heat up a dry cast iron pan for about 10 minutes on high, then throw on the steak. While that is searing the bottom, you can also use a MAP or butane torch to simultaneously sear the top briefly, then flip the steak so the top can pick up some of the fat in the pan. Remove and let stand for a few minutes. If you are cooking outside, or have a better range hood than I do, you can use some grape seed oil or rice bran oil with a very high smoke point, but otherwise a dry pan doesn't make such a mess of the kitchen.

The rendered fat and meat juices can then be added to the fat in the pan, together with some wine and perhaps some mushrooms and butter, and reduced to make an exquisite sauce.

[nathanm]

I've tried corn on the cob SV, but to me, the long cooking time (1 hours at 85C) tends to make the corm taste too "cobby" for my taste. Nathanm, Thomas Keller, and others recommend slicing the kernels off of the cob, and cooking them with butter and other spices as desired -- perhaps my favorite, a little chipotle and lime.

Don't go so hot! With fresh sweet corn 140F/60C is great. I typically do 30 min for corn on the cob, less if it is off the cob in a thin layer in a sous vide bag.

[nathanm]

PedroG, blackp, and I have been debating this issue extensively off-list over the last several weeks, and together we proposed an experiment along the lines above.

....

Then once we can answer that question, we can go on to explore the vacuum variables involved in long term frozen storage-- hard vacuum vs. 90% vs. 80%; and then the even harder issue of whether to use modified atmospheric packaging (MAP), with either nitrogen or CO2. To that end, I'm probable going to add the gas port adapter to my MVS-31X, and start with a pure CO2 mixture. CO2 plus water yields carbonic acid, which might increase the Ph enough to provide a bacteriostatic benefit, as has been reported with chicken in industrial practice

Hopefully there will be a sufficient number of users on this list with the kind of high-end equipment required to do these tests, as it's now apparent that a single user's tests may not be conclusive, due to equipment parameters and god knows what else.

Bob

There is not that much difference in vaccum settings for most situations.

First off, you will never get a very strong vaccum no matter what you do, because the water in the food will evaporate. With any fresh meat or vegetable you can NEVER have a vacuum less than the vapor pressure of water, since you have water in the food. Note that even if the water in bag does not boil, it is nontheless evaporating.

A chamber style machine can draw enough of a vacuum to boil ice water, but there is little point in doing that. In general you want to draw enough of a vacuum to remove the residual air, but since you will never remove all of the water vapor, there is no point in attempting to pull a vacuum stronger than it takes to boil the water. You don't even need to go that far, but certainly there is no point in going farther.

Note that many vacuum sealers have a default program where they take the bag to 99% vacuum then hold it there for 5 to 10 seconds. The reason is NOT to draw the vacuum below 99%. In fact, depending on the temperature of the food it may not even reach 99%. The goal is to bring the bag to the point where the water in the food will boil. This fills the chamber with water vapor, which helps displace the residual air.

Note that a bit of boiling of water in the food like this is not going to hurt things.

Also, note that you are going to cook the food! Which means that ultimately the pressure in the bag is the vapor pressure of water at the cooking temperature. The original pressure in the bag is pretty much irrelevant.

As an example, if you cook at 60C/140F, then the vapor pressure of water is 19.9 kPa. Normal atmospheric pressure is 101.325 kPa. Vapor pressure of water at 5C/41F is 0.9 kPa.

So if you pack some chicken breasts (or other meat, seafood, vegetables) at 5C (typical refriderator temp), then no matter how hard the vacuum pump pulls, you will never get below a vacuum of 99.1% because that the level at which the ambient pressure equals the vapor pressure so the water boils. Realistically, you can draw a 99.0% vacuum but no more than that.

That will evacuate most of the air and thus oxygen, which is your real goal with sous vide vacuum packing anyway. The goal isn't the degree of vacuum, it is getting the oxygen out, and even then you ONLY care about the oxygen in some cases. If you are serving the food immediately and not storing it in the bag then you don't really care about the vacuum level. In fact, you can cook in an unsealed bag.

We seal and vacuum pack for storage, and a bit for convienence (keeps bags from floating...)

OK, so back to the example. If you pull a 99% vacuum at 5C, then seal it, the food bag is now at atmospheric pressure, because the bag is not strong enough to resist the pressure. In most normal cases with soft food, the bag does not contain a vacuum, and it is NOT "under pressure", despite the title of Thomas Keller's book on sous vide. Yes, it is true that atmospheric pressure pushes on the bag, but the atmosphere pushes on everything, so that doesn't count for anything meaningful.

The only real difference is that if you have a hollow space inside the food - a bubble or cavity - then in the atmosphere that cavity pushes back with the same atmospheric pressure. So, if you vacuum pack, you take that pressure out of the cavity, and it tends to collapse. Hollow foods - say a green pepper - will collapse in the vacuum bag. Stronger hollow foods - say a quail or cornish game hen - sealed in a vacuum bag are generally strong enough to resist the atmospheric pressure, so in that hollow space there will be a partial vacuum.

If you looked closely you would find that the bag has a small amount of gas in it - which is the residual air, and a small amount of water vapor. This is particularly true if the food has a hollow space, but it is even true for a soft food.

When you heat that bag up to 60C the residual air will expand a bit, and more water vapor will evaporate.

In fact, the amount of air and water vapor would be the same as if you vacuum packed the food at 60C temp, at which point you would get about an 80% vacuum.

Now, it is not true that you get a "80% vacuum in the bag" because for most foods there never is a vacuum in the bag once it is sealed. For a soft food, the amount of residual gas in the bag would be identical to one sealed at 60C, at which point the lowest possible vacuum in the chamber would be 80%. For a hard food with a hollow space in the middle, that hollow space would have a parial vacuum of 80%.

If instead you sealed at 90% vacuum at 5C, then heated the sealed bag up to 60C, the amount of residual gas would be a bit more - equivalent to sealing at 68% vacuum.

So, as you can see, there is not that much difference.

Some people, like Dave Arnold, say that they get big differences in results by their vacuum level. I totally respect Dave and his team, and we use many of their discoveries in MC, but I am not sure how to respond to this. In our tests we don't see a difference in the final quality. As the example shows the laws of physics pretty strongly suggest that there can't be much of a difference. My guess (but only that) is that there are some other issues at play here in how the food is handled, but I don't know for sure.

Fish are a particularly amusing example. It is often claimed that fish "can't take the extra pressure" of high vacuum packing.

First off, at a normal cooking temperature, there is very little difference in the amount of air in the bag. Fish don't typically have hollow spaces in them, so this is a moot point.

One reason that fish typically don't have hollow spaces is that fish can generally swim pretty deep. Almost any fish can swim 33 feet (10 meters) deep, at which point the fish is under TWICE atmospheric pressure. At 66 feet / 20meters it is 3 atmospheres and so forth.

Deep dwelling fish, like a monkfish live routinely in a 10-20 atmospheres of pressure.

So, fish, all of animals, are built to take a lot of hydrostatic pressure, and thus should not have a sous vide pressure effect.

Finally, note that "bag pinch" where you can see where the bag came together can affect any food, but that little bag seam is not generally a quality problem.

[Robert Jueneman]

PedroG, blackp, and I have been debating this issue extensively off-list over the last several weeks, and together we proposed an experiment along the lines above.

....

Then once we can answer that question, we can go on to explore the vacuum variables involved in long term frozen storage-- hard vacuum vs. 90% vs. 80%; and then the even harder issue of whether to use modified atmospheric packaging (MAP), with either nitrogen or CO2. To that end, I'm probable going to add the gas port adapter to my MVS-31X, and start with a pure CO2 mixture. CO2 plus water yields carbonic acid, which might increase the Ph enough to provide a bacteriostatic benefit, as has been reported with chicken in industrial practice

Hopefully there will be a sufficient number of users on this list with the kind of high-end equipment required to do these tests, as it's now apparent that a single user's tests may not be conclusive, due to equipment parameters and god knows what else.

Bob

There is not that much difference in vaccum settings for most situations.

...

Some people, like Dave Arnold, say that they get big differences in results by their vacuum level. I totally respect Dave and his team, and we use many of their discoveries in MC, but I am not sure how to respond to this. In our tests we don't see a difference in the final quality. As the example shows the laws of physics pretty strongly suggest that there can't be much of a difference. My guess (but only that) is that there are some other issues at play here in how the food is handled, but I don't know for sure.

...

Thanks, Nathan -- first of all for your stupendous effort with MC -- surely one of the very few cookbooks likely to be referred to by most chefs and foodies by an abbreviation, but one that will surely sit side by side with Escoffier and Larousse for the next century. And second for this post, which I need to think about a lot more, and try to confirm or disprove for myself, experimentally. But your explanation certainly makes sense.

Bob

[Robert Jueneman]

I've tried corn on the cob SV, but to me, the long cooking time (1 hours at 85C) tends to make the corm taste too "cobby" for my taste. Nathanm, Thomas Keller, and others recommend slicing the kernels off of the cob, and cooking them with butter and other spices as desired -- perhaps my favorite, a little chipotle and lime.

Don't go so hot! With fresh sweet corn 140F/60C is great. I typically do 30 min for corn on the cob, less if it is off the cob in a thin layer in a sous vide bag.

Thanks, Nathan.

Do you have a time/temperature recommendation for frozen corn on the cob, which we are going to have tonight?

Bob

[nathanm]

Sorry, I don't have experience with frozen corn.

I would try it at 60C/140F.

A wild guess is that it will take an hour. I would put it in with an hour (or maybe a bit more to be safe) before the meal, and then test at 30 min and 45 min.

[PedroG]

.....

Some people, like Dave Arnold, say that they get big differences in results by their vacuum level. I totally respect Dave and his team, and we use many of their discoveries in MC, but I am not sure how to respond to this. In our tests we don't see a difference in the final quality. As the example shows the laws of physics pretty strongly suggest that there can't be much of a difference. My guess (but only that) is that there are some other issues at play here in how the food is handled, but I don't know for sure.

.....

Thank you, Nathan, for all you did for the community and for your plausible explanations.

Do I get something wrong, or are the tests you mention in contrast to what you write in your book?

Boiling not Crushing

.... By evaporating rapidly into water vapor, the expanding steam does a lot of damage to the food, even though it is not hot. Cells rupture and are pushed aside to create channels. During cooking, juices leak out of the food through these channels, drying the food and damaging its texture. ....

To answer the question "boiling or crushing", I suggest the following experiment with three similar cuts of chicken breast and/or fish:

1. Expose to maximum vacuum (99%+30sec), do not seal, release vacuum, seal at 80% vacuum. -> boiling, no crushing.
   
2. Seal at 99%+30sec vacuum -> boiling and crushing
   
3. Seal at 80% vacuum -> no boiling, no crushing
   

To prevent floating with 80% vacuum sealing, either use an edge sealer for 80% vacuum, or try to squeeze most air out of the bag before sealing in the chamber sealer as I suggested upthread.

Cook chicken at 63°C to pasteurizing conditions according to thickness, or fish at 48°C as Dave Arnold did.

Check liquid loss by aspect and by weighing. Check organoleptic outcome by blind testing.

As I have only an edge sealer, I can't contribute to these experiments.