977 replies to this topic

[pounce]

The theory of SV is interesting and important, indeed. Personally, I would like to concentrate on SV recipes, techniques and experiences, at this time.

Does this mean you are giving up and admitting the material in your books is incorrect and in some cases confusing to the point that it may as well be incorrect? I just want to know before I spend the time pointing out the flaws. If you are giving up I will as well.

[edsel]

As to the stuff on Page 76:  I believe Roca must be talking about cooking food in a rigid container rather than a flexible container.  As I and others have mentioned, it is possible to go under 14.7 psi in a rigid container -- it's just not possible in a container as flexible as a bag, because the container deforms until there is pressure equilibrium.

I have to admit that I was baffled by some of the statements in the Roca/ Brugués book, but I mostly glossed over the confusing passages in favor of the seemingly definitive information about sous vide cookery contained in the book. I still value the practical application information in the book, and I think the discussion of sanitation issues is accurate, but MikeTMD's citation of the stuff about vacuum, etc., gave me pause. I had to go back to page 76 to see for myself.
There's no question that Roca et al. state that water behaves differently under reduced pressure. However, it's implied that this applies to food sealed in a bag:

In the vacuum, the atmospheric pressure acting on the packaged product causes water to vaporize before it would in conventional cooking, in which pressure does not have as great an impact on the final result (this means that the food will experience the effects of water vaporization at lower temperatures, along with all of its consequent  modifications). This is therefore a very important fact that distinguishes sous-vide cooking from traditional methods.

(my emphasis added)
This discussion is accompanied by FIGURE 1 / Effect of temperature-pressure relationship on water states. The figure shows the lowered boiling point of water vs. reduced pressure. As Sam has pointed out, this would only apply when the food is sealed in a rigid container. Roca et al. seem to be talking about sous vide cooking as we know it (food sealed in a bag). So this part of the "definitive" book on sous-vide would appear to be incorrect. Perhaps the very term "sous vide" is unfortunate, since it leeds people to think that the food is actually "under vacuum" when cooked, rather than just vacuum-sealed.

[MikeTMD]

The theory of SV is interesting and important, indeed. Personally, I would like to concentrate on SV recipes, techniques and experiences, at this time.

Does this mean you are giving up and admitting the material in your books is incorrect and in some cases confusing to the point that it may as well be incorrect? I just want to know before I spend the time pointing out the flaws. If you are giving up I will as well.

I never meant for this discussion to become competitive - my primary goal is to learn what can I do to enjoy better food ( prepared by others, or otherwise). So it is not about "giving up", or "staying the course".

There is a difference of opinions - no doubt, but every point of view should be heard. As such, please share yours.

[MikeTMD]

... part of the "definitive" book on sous-vide would appear to be incorrect. Perhaps the very term "sous vide" is unfortunate, since it leeds people to think that the food is actually "under vacuum" when cooked, rather than just vacuum-sealed.

Do you mean vacuum sealed by FoodSaver type equipment? I am not very familiar with FS - does it just vacuum-seal the cooking bags, or does it create some kind of vacuum? ( I always used a vacuum chamber machine packaged food - sometimes at the cost of having better vacuum over proper and essential seasonigs and spices)

Edited by MikeTMD, 10 May 2008 - 08:38 PM.

[pounce]

I always used a vacuum chamber machine packaged food - sometimes at the cost of having better vacuum over proper and essential seasonigs and spices

Do you mean to say you don't have a vacuum sealer and that you are cooking cryovac'd foods in the plastic you purchased them in?

[MikeTMD]

I always used a vacuum chamber machine packaged food - sometimes at the cost of having better vacuum over proper and essential seasonigs and spices

Do you mean to say you don't have a vacuum sealer and that you are cooking cryovac'd foods in the plastic you purchased them in?

I usually ask a mom-pop butcher down the street to use their vacuum-chamber machine to seal my bags after I fill them ( for a $1 per bag - truly a bargain). That said, I buy Cryovac'd portioned flat iron steaks and hanging tenders from a wholeseller, and - guilty as charged, SV them in the industrial strength vacuum bags they come in, but season them agressively prior to browning.

Edited by MikeTMD, 10 May 2008 - 09:01 PM.

[slkinsey]

Mike: Do you agree that putting these questions to a heavily credentialed (member of the National Academy of Sciences, etc.) physical chemist should settle these questions?

I think this is important for more than deciding "who is right" on this question. First and foremost, it should clarify some material questions as to these cooking techniques. Second, it will allow us to move on to more important and stimulating discussions in this thread.

[e_monster]

Mike,

I think that you are conflating several meanings of 'vacuum'. You are conflating the sense of vacuum as 'void of oxygen' with the sense of 'at 0 pressure'. In common parlance, 'vacuum' is generally used pretty loosely -- and these meanings are commonly interchanged even though they are not the same. (Vacuum-packed, as an aside, means PACKED in a vacuum. A chamber sealer does have low pressure while sealing, but that condition ends when the chamber is opened and air rushes back in to the chamber.)

If you void air from a rigid container that contained only air, you would approach a vacuum inside. (You would not get a true vacuum however.) However voiding air from a plastic bag does not result in a less than atmospheric pressure inside the bag once the bag is exposed to atmospheric pressure.

Even if one has a vacuum bagging machine capable of voiding all the air from the bag, as soon as the bag is exposed to atmospheric pressure, the contents are also exposed to atmospheric pressure. The bag provides 0 protection from pressure. If Roca claims otherwise (and it is NOT clear that he does claim otherwise from the quotes you provided), he is mistaken.

(The quotes from page 85 are reasonably explicit in stating that the contents of the bag are exposed to pressure. He says there that it "stop aromas from volatilizing". At low pressure, aromas volatize more easily because vaporization points are lowered. I find some of the quotes you provided to be either poorly written, translated or edited (no way of knowing which) as they do seem to confuse a few issues, but that isn't really germane to the question at hand.)

Here are a few tests that I believe demonstrate that the bag does protect the contents from external pressure:

1) Vacuum pack your meat. Now, press the bag and watch the meat deform in response to the pressure. The reason that it deforms when pressed is because the bag provides no protection from external pressure.

2) Vacuum seal some ice cubes in a bag. Place the bag in some water that is below boiling point but still hot. Let's say 190F if you are near sea level. Does the water inside the bag boil/vaporise? If not, then you don't have a situation anywhere near approaching 0 atmospheric pressure. (Water vaporizes at a VERY low temperature in a real vacuum). You can more or less measure the pressure to which water is subject by measuring the temperature at which it boils.

If you perform those same experiments with a rigid container, you will get very different results. The container will prevent you from deforming the meat and the water will boil at a lower temperature. (By measuring the temperature at which it boils you can also learn what the pressure is inside the container)

Here is another test. Vacuum pack a marshmallow in a rigid container. Vacuum pack a marshmallow in a bag. The marshmallow vacuum packed in the rigid container will expand. The vacuum packed one will be crushed. (If you have a chamber sealer you would see that the marshmallow expands while the vacuum condition exists and then is crushed as pressure equalizes.)

(As an aside, someone has pointed out to me "if one were able to reduce the pressure to, say 0.5 psi, the boiling point of water would be only around 27C/80F. Lower pressure than that, and the water inside the meat would boil at room temperature. This would not generally be a good thing if one were cooking a steak.")

Hopefully Prof. Kinsey will give us the final word soon.

[pounce]

I usually ask a mom-pop butcher down the street to use their vacuum-chamber machine to seal my bags after I fill them

I think not having any sort of vacuum machine to experiment with puts you at a disadvantage when talking about the real world effects of some of the science involved.

“We can broadly define cooking sous-vide as heating the food previously sealed in an airtight and heat-resistant container whose atmosphere has been modified ( a vacuum has been produced,, with or without elements such as gases, liquids, etc.).”

It appears to me that they might be using the term "Atmosphere" in an inconsistent way in their book and this is causing confusion. In general with SV when you change the atmosphere you are reducing the oxygen and not creating a vacuum state. SV is often associated with MAP (Modified Atmosphere Packaging). You see MAP all the time in grocery stores. In all cases the package is sealed (and may even be lose fitting) but has a cavity of some form of gas (normally Nitrogen 70% and Carbon Dioxide 30 %). Lots of fresh pasta and more and more meat trays are packed this way. MAP extends storage life by removing oxygen. Often the contents of the packaging is fragile and would crush if you removed the oxygen by removing all gases (berries, chips, baked goods etc). Instead of removing the gas void in the packaging like vacuum sealing the manufacturer just replaces (or in some cases never introduces) oxygen in the packaging. In the food packaging industry "atmosphere change" means to make a change in the normal composition of air (78.08% nitrogen 20.96% oxygen 0.03% carbon dioxide). It does not mean pressurize of sustain under vacuum. A vacuum sealer does change the atmosphere of the packaged good by removing or changing the composition of air before sealing and returning the packaged goods to normal pressure.

”6. In sous-vide conditions, water vapor forms at much lower temperatures than in normal atmospheric pressure conditions.”

At 20hg vacuum water boils (vapor pressure) at 157 degrees Fahrenheit. If you were cooking something in a rigid vacuum chamber you could boil water at room temps. The problem with the statement from the book is that you don't have a vacuum in the bag outside of the vacuum sealing chamber so you have not lowered the vapor pressure point of water.

Say you are using a chamber style vacuum sealer. For this example let's say that the vacuum sealer can pull a vacuum low enough to boil water at room temperature. You put a vacuum bag in the sealer and add some water. You close the sealer and pull vacuum until the water in the (currently unsealed) bag starts to boil. You can see this through the clear top of the vacuum sealer. You now seal the bag in the chamber and release the vacuum. You take the bag out of the vacuum sealer and put it on the counter. Is the water still boiling? Why not?

Imagine that your vacuum bag material is very thin. Take a small air filled balloon and measure it's circumference. Put this balloon into the bag and vacuum seal it. Take the vacuum sealed bag out of the sealer and measure the circumference of the balloon inside the bag. Is there a difference? Why not?

Put the vacuum sealed balloon into a vacuum chamber and draw a vacuum. Does the circumference of the balloon change? Why?

Even if you do lower the vapor pressure of water in a rigid sealed container you still need heat to "cook". What if you are boiling water at room temperature in a vacuum and put a raw egg in the water. How long do you think you will have to boil the egg until it's hard cooked? That said using a vacuum to reduce a liquid can have a really nice effect, but in this case the vapor needs to be evacuated out of the vacuum chamber. This sort of reduction can be done very easily at home with a $10 aspirator and a rigid container.

“Sealing in shrink bags: guaranteed pressure”

Yes. If the bag material is elastic and designed to shrink using heat it is possible that this could add more pressure to the contents of the bag than what is normally present at normal pressure outside of the bag. Very few Sous Vide bags do this however. This will mostly be things like Cryovac brand material. To be sure there is no vacuum inside the package when the package material is essentially squeezing the contents. In reality its also really not that much pressure.

[MikeTMD]

Mike:  Do you agree that putting these questions to a heavily credentialed (member of the National Academy of Sciences, etc.) physical chemist should settle these questions?

I think this is important for more than deciding "who is right" on this question.  First and foremost, it should clarify some material questions as to these cooking techniques.  Second, it will allow us to move on to more important and stimulating discussions in this thread.

I agree with you 100% - lets ask a proficient physical chemist for clarification, and move on to other SV related issues.

[slkinsey]

Okay, so I just got off the phone with my father (this is he, if anyone is curious as to his qualifications). He says:

1. When the air is removed from a sous vide bag and the bag is subsequently exposed to normal atmospheric pressure, the contents of the bag are also under normal atmospheric pressure. This is because, for purposes of our consideration, the bag is infinitely flexible, and it deforms by reducing in size until the interior of the bag is at the same pressure as the exterior of the bag.

2. The only way to achieve lower pressure is with a rigid container.

3. There would be no significant difference as to oxidation reactions between a steak sealed in a bag using a FoodSaver and a steak sealed in a bag with a powerful chamber machine. The difference in the amount of oxygen available for reaction in the two examples is negligible, considering that the steak already contains oxygen.

[Vicious Wadd]

I'm just jumping into this forum, so bear with me...

Has anyone tried cooking in plastic within a Foodsaver bag?

Case in point, I recently picked up Michel Richard's "Happy in the Kitchen," and tried the neo-chicken salad recipe last weekend using PVC-free saran in a water bath.

Use of the wrap was critical to obtaining the log shape. In comparison, the Foodsaver looks like it will only follow the natural, unrolled shape of the chicken breast. So to replicate that recipe using the watertight wrap from the Foodsaver, I thought I could make the chicken logs in the saran first, and then vacuum wrap them prior to cooking.

Anyone tried something similar in terms of pre-shaping with plastic wrap?

Thanks,

- VW

[pounce]

Sure, works pretty good. If you can pulse the vacuum and use your free hand you can position the FS bag around the item... that sounds oddly....

[slkinsey]

I have done this a number of times. For example, for Thanksgiving I made a turkey ballotine that consisted of turkey breast filled with a turkey mousse with foie gras and black truffles. To do this, I pounded out a large turkey breast to uniform thickness, put a line of turkey mousse down the middle and used plastic wrap to roll the whole thing up like a sushi roll. I then twisted the ends of the plastic wrap to tighten the whole thing up as much as possible, and then sealed the plastic-wrapped "turkey log" in a vacuum bag. I made similar "logs" of bacon-wrapped cornbread dressing and braised dark meat with Savoy cabbage wrapped in turkey skin -- all using plastic wrap to help form and hold the logs in place. These were all cooked sv to 60C.

Here is an image of me cutting slices of turkey ballotine:

And here is a closeup image of slices of the three different elements on the plate:

[nickrey]

I am using a slightly different sealer but with the same mechanism and the same result occasionally.

As a matter of habit now, I vacuum seal using the normal process then move the bag slightly and reseal without vacuum (actually, being a teeny bit obsessive compulsive, I do this second step twice).

Hope this helps

I have used the FoodSaver hundreds of times and have never had a good seal break BUT it is possible to  create a less than optimal seal if you aren't paying close attention and either get the area where the seal will be too wet OR have a tiny tiny little wrinkle that keeps the bag from being sealed well. I think if you inspect the seal after it is done, you won't have any problems.

When vac-packing moist foods, it is possible to have an improperly sealed bag without realizing it. It is also possible to have a little wrinkle that interferes with sealing. A few weeks ago, I was a little careless and vac-packed a porkloin with a wee bit of marinade. The seal seemed fine (i.e. the bag shrunk down and didn't expand when the FoodSaver was opened. I put the bag in the fridge and when I took it out half an hour later, the bag was no longer tight around the food. Upon close inspection, there was a small area where the bag had not really sealed well. It was pretty obvious when I looked at it.

sygyzy,

The results you got are not unusual, and in fact could be quite desirable, although the broken seal doesn't make for the best SV experience ( we all have seen it happened , though).

Does anyone know why this happens? I know Food Saver says you can put their bags in boiling water so the 130-140 F water shouldn't have mattered.

[sygyzy]

It certainly does help and it actually makes perfect sense. If you notice the Foodsaver's strip looks pretty wide (maybe 3/8") but I think it actually only seals a small 0.5mm section. Moving the bag forward and backwards means wider sealer.

[qrn]

On every seal on the f/s , after it stops .I slide thebag out an 1/8" or so and re seal. seems to help...The seal line is very narrow.
Bud

[Mikels]

Maybe I can help. What we are doing is removing the air in the bag. This is a true vacuum. Were it in a solid vessel, the same amount of air would remain. Since the walls are flexible the bag conforms to the food inside, creating a surface that comes close the food. As I see it, that is the primary reason for removing the air. Otherwise, the air would cause the bag to float and insulate the food from the water. However, once you put it in the bath, the vapor pressure will increase, thus reducing the vacuum. If you want to further reduce the oxygen, you would need to purge the bag before creating the vacuum with an inert gas. By the way, I was a physical chemist.

[pounce]

An easy and readily available way to simulate gas flush at home with a FoodSaver vacuum sealer is:

• Seal item as normal.
• Carefully clip corner off the bag allowing a hole smaller than a pencil
• Insert nozzle of Wine preserver like Private Reserve, WineLife, Cork Pops, etc (Nitrogen, Argon, Carbon Dioxide etc in an easy to use $10 can) and fill the bag with gas.
• Insert open corner of bag in Food Saver and vac out the Wine Preserver gas and seal.

Edited by pounce, 12 May 2008 - 07:44 PM.

[slkinsey]

You could to the gas flush thing also using a tiny piece of dry ice:

1. Seal item together with small piece of dry ice as normal
2. Clip off small corner of the bag leaving small hole
3. Allow dry ice to melt
4. Insert open corner into FoodSaver, vacuum out CO2 and seal.

[Mikels]

I have been experimenting with long (18+ hours) cooking times using coq au vin as the dish. It produces incredibly intense flavors. Most of what I have seen focuses in single cuts of meat. Does anyone have experience in this area?

[slkinsey]

Experience in what area, exactly? Could you be more specific?

[BRM]

All of this has got me thinking a bit. If one did, in fact, seal food in a rigid container so that it would be held at less than atmospheric pressure, would there be any advantage to cooking it this way?

I suppose the vacuum would make heat transfer less efficient and the water in the food would evaporate away at a much lower temperature and therefore 1) decrease the vacuum and 2) dry out the food but I am curious what others think. Sorry to report I am not a physical chemist but I did get an A in it in college.

I could actually do this BTW. I have the little Foodsaver gadget that pulls vacuum on mason jars. I have no idea what the final pressure in the jars is when the machine shuts off.

I suppose it would have to be something that you wanted to dry out and thought that doing so at a lower temp was a good thing...meringue cookies maybe.

I'll go back to work now...

[pounce]

Yes, up thread we discussed the vacuum frying of things like potato chips and fruit chips etc. By frying in vacuum you still get a crispy chip, but you don't get the supposed harmful byproducts of the frying. Vacuum frying is used in production chip/crisp making process'.

[slkinsey]

There are lots of interesting things you can do with sv equipment that is not exactly sv cooking. For many of these things, you really do need a more powerful vacuum. I set forth some of these things above, but for example, you can compress fruits and vegetables to change the texture or you can "pressure wilt" raw vegetables to approximate some of the structural changes of cooking without actually cooking the food. In terms of reduced pressure, you can put a food into a rigid container together with a liquid, reduce pressure (sucking all the air of of the food item) then release pressure, whereupon the food will "suck" up the liquid into the spaces previously occupied by air (this works best for things like cucumber or watermelon).

[MaxH]

I have been experimenting with long (18+ hours) cooking times using coq au vin as the dish. ... Does anyone have experience in this area?

Just as an aside, this reminds me of the prosaic but related crock pot.

(For anyone who doesn't remember the time or place, crock pots became a trendy US consumer appliance maybe 25 or 30 years back, with general publications suddenly full of recipes using them, housewares shops devoting departments to them, etc. Like microwave ovens earlier, and automatic bread machines later. Like automatic coffee makers in the 1980s, cocktails and their equipment in late 1990s, crêpe pans in early 1970s, panini grillers today, etc. etc.)

[Mikels]

There is a difference. A crock pot is an open system, whereas in sous vide we have a closed system. In one experiment, I cooked my test dish three ways: traditional, crock pot and sous vide. The prep was used in all three cooking methods. The sous vide was not only better than the crock pot, but better than the traditional treatment. I attribute this to the fact that by cooking it longer and in a sealed bag, the flavors are enhanced. When the recipe was adjusted, it was vastly better.

[Mikels]

All of this has got me thinking a bit.  If one did, in fact, seal food in a rigid container so that it would be held at less than atmospheric pressure, would there be any advantage to cooking it this way?

I suppose the vacuum would make heat transfer less efficient and the water in the food would evaporate away at a much lower temperature and therefore 1) decrease the vacuum and 2) dry out the food but I am curious what others think.
....
I'll go back to work now...

I think it is important that the food has the greatest contact with the water. Because there is a vacuum, atmospheric pressure plus any water pressure pushes the bag so there is no air to insulate the food.

However, if you filled the container completely full, you would have the same effect. No vacuum would be necessary. The liquid in the food would have the same temperature as the water, thus having the same effect as in a bag.

[Mikels]

Experience in what area, exactly?  Could you be more specific?

Long term (18+ hours) cooking or cook and hold. I am interested in slow cooked dishes: braising or stewing. While this is not conventional sous vide, it raises an interesting question: what effect does the composition of the braising liquid have on the dish; does it behave like a marinade, where the osmotic difference between the liquid and the meat either increases or decreases the water content of the meat? Aside from freezing any liquid used, are there any other techniques that may help?

I have read about brisket in earlier posts. Two temperatures are mentioned: 131F and 145F. This raises the question: is it less likely the gelatin remains in place at the higher temperature.

[slkinsey]

So you're talking about LT/LT cooking that is not in a sealed container? Essentially, using a really accurate Crock Pot set to a low temperature?

Or are you talking about sous vide cooking with a lot of liquid in the bag together with the meat?

As for one of your questions: Since we are cooking the meat, there is no way it is going to end up with more water content than it started out with. It will always be less.

As for using liquids in the bag, it's not clear to me that there is any advantage to using more than simply the amount required to surround the meat once the air is evacuated from the bag.