Sous Vide: Recipes, Techniques & Equipment (Part 1)

[alexw]

sorry should have said that the fennel needs to be finely shaved on a chinese vegetable slicer, dont try the whole bulb cos that will take weeks and probably blow up your microwave.

[megwoo]

Thanks alexw!

Yes, this helps alleviate my worries. Thanks for the tips, I can't wait to start experimenting.

P.S. Fennel veloute sounds great!

[mjc]

thanks nathan.

I tried the turkey again on saturday. I cooked it at about 155 for about 4.5 hours. My family usually cooks their turkey breast to 180!, so I tried to compromise on the temp. Anyway, it turned out great and was the best turkey I or anyone ever had. Unfortunately, in the rush to get it to the table in the end, i forgot to check the final temp. I'll defintely try sous vide again in the future and take better notes.

[johnsmith45678]

I'm unclear on why food which has been vacuum sealed cooks at a lower temperature than non-vacuum-sealed food does. Obviously the pressure internal to the seal is still a single atmosphere, because the plastic seal isn't strong enough to maintain an actual vacuum. Could someone explain this to me?

When I first read about sous vide, I assumed that a sous vide cooker had an actual vacuum chamber. Of course, that would tend to freeze dry food, but it's an interesting question what happens if you heat up freeze-dried food under a vacuum, then moisturize it after cooking. Does anybody know if that might be a viable cooking technique?

Oddly, some quick web searching seems to indicate that there aren't currently any commercial freeze dryers on the market.

http://www.livejournal.com/users/bramcohen/24605.html

I don't think I have a good answer myself!

[jackal10]

Err...there are two separate things going on in sous vide cooking.

The cooking is long time low temperature, but at atmospheric pressure, or near enough, The vacuum bagging is to keep the food sealed, in contact with whatever sauce and stop it drying out. The bag also separates the food from the cooker medium, often a water bath which is a convenient way to accurately control the temperature.

Some claim the vacuum opens the pores of the food and permits greater penetration of marianade, sauce or whatever, but I have my doubts.

I doubt if cooking freeze dried foods will have much effect, until you get to temperatures where they burn and char. Most cooking reactions need to include water. The cell structures of freeze dried foods are already fairly disrupted, - rehydrate a piece of freeze dried steak, and you don't get back a raw juicy ribeye, alas - its more like beef jerky.

[Mallet]

I think the basic premise of that online discussion is wrong (at least they seem to be be led off track ). While it's true that the actual cooking temperature is lower than non sous-vide food, the final temperature is the same. The first post seems to imply that the author thinks that sous-vide food cooks 'more' at a lower temperature by virtue of the vacuum, which of course it doesn't.

[jsolomon]

Cooking in a vacuum wouldn't work the way I think most of you are pondering.

It is true that water will boil at a lower temperature in a vacuum, but that doesn't speak at all to the amount of kinetic (thermal) energy in that boiling water.

Water that boils at 50C in a partial vacuum will cook like water at sea level that is... 50C.

So, if you have a reaction that will only "go" at 60C or above, it won't "go" if you drop the pressure so water will boil at 50C and try it at 50C. The energetics just don't calculate up.

The same thing works with cooking. So, it's not the partial (I'm with jackal10 on that being nominal) vacuum. What it is, is the time that the food is kept at this lower temperature. It cooks slowly and evenly, and the water bath provides even heat around the whole item (if it's submerged).

[nathanm]

As Jackal10 has pointed out, there are several things going on with sous vide.

The food is NOT cooked in a vaccum - it is at ambient atmospheric pressure.

The vacuum packing in the bag simply ensures that there is less air trapped in the bag that might otherwise be there.

There are several reasons to remove the air:

- The bag would float if cooked in a water bath, and thus not cook evenly because the top portion would be out of the water.

- Some food oxidizes (endive, artichoke) while cooking and that is lessened.

- Reduces microbial growth during cooking. This is only relevant for very low temperatures (below 54C/130F).

- Reduces both oxidation and microbial growth during cold storage after cooking. This was the original motivation for a lot of sous vide cooking - the idea was to prepare food centrally then reheat it for service at other locations, for example for airplane catering. Note that most meat, and many other products, are vacuum packed during storage for preservation regardless of whether they are cooked in the bag.

- Sealing the bag has various advantages (keeping flavor in, keeping water and other things out) and while you could seal the bag without removing the air, the air will tend to expand upon being heated. The bag would stretch or expand like a ballon if sealed with air trapped inside. This makes floating worse if you use a water bath, and could pop the bag.

- There are other methods of cooking that use hermetically sealed containers to retain moisture and flavor, but they are not very convienent. Roasting in a salt crust is one example. Roasting in a pan sealed with dough around the pan lid is another example. However they tend to do an imperfect job of sealing, and they are not very convenient.

- Once you have the full set up of a very temperature stable cooking environment (like a water bath), and you hermetically seal the food (so it retains flavor, so it can't boil over, or dry out) then it is more convenient to cook things unattended for long periods of times. Cooking something for 36 hours on the stove, or in a conventional oven, is possible but would require a lot more hand holding. Sous vide is the easiest and most trouble free way to do really long cooking times.

The flip side of these reasons is that you can in many cases achieve a very similar effect without using a bag, or without removing the air. One example is with a combi-oven which allows low temperature steaming. Another example is low temperature poaching in water, or in oil/fat (confit). This is certainly possible in many cases.

As an example, there is a pseudo-sous vide approach where you put food in a non-vacuum sealed bag that has a one-way valve in it. The food is cooked in combi oven under steam - the trapped air in the bag expands and exits via the valve. When the product cools the result is a vacuum (not very high) in the bag. This is relevant if you don't want to use a vacuum packer, but want to store the food in the bag and reheat it later, so you want the improved preservation of having a mild vacuum.

As Mallet points out, the temperature in sous vide is not related to the fact that the food is packed in a bag. Temperature works the same way, and you can cook at low temperature without the bag. However, it is easier on the chef to cook for a long period of time if you can hermetically seal the food (so it won't dry out etc).

Sous vide as a cooking technique has evolved from being oriented mainly as a food preservation techinque for cook-and-hold, to a much broader set of things. The fact is that sous vide today mostly uses vacuum packing as a convienence. As Jack says, it is convienent to use a water bath for maintaining temperature accurately. If you don't want your food water logged, the vacuum bag helps you poach it without water contact. In other cases it is oxidation, or wanting to seal the bag that motivates it. While you can do many of these things without a vacuum bag, once you have the vacuum bagging machine and the water baths etc, then it is very convenient to use it for many purposes.

Truly cooking in a vacuum is a very different thing than sous vide. As jsolomon points out, cooking in 50C water under vacuum is for most purposes the same as cooking in 50C water at another pressure so in that case there is no difference.

However, there are some scenarios where cooking in a vacuum makes sense:

- Marination is in general improved by being done in a vacuum. There are two reasons. The first is that trapped air is removed - there is air trapped in just about everything and degassing the food under marination tends to remove that trapped air. If there is liquid present in the degassing, it will tend to get sucked into the pores to replace the air bubbles as they are removed. In addition, it can help osmosis to change the ambient pressure. Vacuum marinators, and vacuum tumblers, are commercial equipment used extensively in meat processing to do marination in a vacuum.

- A vacuum reduces the vapor pressure of water and other liquids, so you can dry or dehydrate things better in a vacuum that at ambient pressure. That either means you can dry them faster at the same temperature, or you can dry them at a lower temperature. Vacuum dessicators are common in laboratories.

- Freeze drying is mentioned in the thread. This is a special case where you dehydrate at very low temperatures, using a high vacuum. It is only important in cases where you really need the low temperature while dehydrating, otherwise normal dehydration works.

- Vacuum distillation lets you distill volitile fluids at a lower tempertaure than under ambient pressure.

There are some chefs experimenting with each of these true vacuum cooking technques, but it is much less common than sous vide. Strickly speaking, vacuum cooking is totally different than sous vide, becaues sous vide is actually cooked at normal atmospheric pressure. The only time you have a vaccum in sous vide is in the packing machine, not during cooking.

[jsolomon]

I haven't seen the packing machines for sous vide. Are they really able to pull a vacuum, or can they just do the same effect as sticking a straw in and collapsing the bag?

[edsel]

There are two types of vacuum machines.

The clamp machines (like FoodSaver) leave the bag exposed to the surrounding air, so the bag collapses as the air is withdrawn.

Chamber machines enclose the entire bag. The air is sucked out of the chamber, the heat sealer clamps down on the bag opening to seal it, and then the vacuum is released. The bag doesn't collapse until the air rushes back into the chamber - kind of fun to watch.

[Shalmanese]

Apart from Sous Vide, there are several other LTLT cooking techniques. LT poaching (in either water, stock or olive oil) works very well for fish, seafood, chicken and perfect softboiled and hard boiled eggs if you have the patience. LTLT roasting produces perfectly cooked, tender roasts. Heston Blumenthal has a method of making mashed potatos which first involves a 2 hour poach in 70C water.

[ned]

There are two types of vacuum machines.

The clamp machines (like FoodSaver) leave the bag exposed to the surrounding air, so the bag collapses as the air is withdrawn.

←

I recently got the new generation Food Saver that claims to be able to handle "moist" contents. I've "sous vided" and poached a small pork shoulder as well as two pairs of trotters. In each case, to varying degrees, the bags have inflated while cooking. Is this about the seal? Expansion? Poor Food-Saver technique on my part?

[jsolomon]

I would tend to say the latter. What were you using as extra "moisteners"? If you added liquid, you may want to microwave it for a bit (2 min or so) to de-gas it. You may also want to attempt to pull suction with a straw (if possible) before using the Food-Saver to help remove some of the trapped gas in simple pockets.

[jackal10]

Another trick is to freeze the liquid portion first.

[ned]

The meat itself was a little wet with blood I guess, and in the case of the shoulder I added duck fat which was fridge temp. I had cleaned veg so maybe they were damp but there was no standing liquid. Could the little bit of what is maybe best described as ambient wetness be the cause?

[ned]

. . . and if so then the seal is compromised?

[pounce]

However, there are some scenarios where cooking in a vacuum makes sense:

There is also a very interesting advantage to frying in a vacuum. Acrylamide is a harmful chemical (known to cause cancer) found in fried starchy foods like potato chips. The chemical is increased with high frying temeratures. By putting the cooking under a vacuum you can lower the fry temperature and reduce the amount of acrylamide you generate duing the cooking by up to 90+%.

An interesting bit of information is that there are a lot of chips out there that far exceed the proposed safe levels of acrylamide in the state of California.

• Cape Cod Robust Russet: 910 times
  
• Kettle Chips (lightly salted): 505 times
  
• Kettle Chips (honey dijon): 495 times
  
• Pringles Snack Stacks (pizza-flavored): 170 times
  
• Lay's Baked: 150 times
  

For those interested there is information about prop 65 here: http://www.oehha.ca.gov/prop65/acrylamide.html

Edited December 1, 2005 by pounce (log)

[nathanm]

In each case, to varying degrees, the bags have inflated while cooking.  Is this about the seal?  Expansion?  Poor Food-Saver technique on my part?

←

Usually, when that happens the reason is that you don't have a very good vacuum in the bag, and the residual air has expanded when heated.

If you have alcohol in the bag, then you can expect expansion when the alcohol boils, which is at 175F.

If the bag isn't sealed properly then you typically don't get a big expansion, because the air just leaks out. If you push on the air in a leaky bag it will go out.

A way to check if the seal is compromised is to submerge the bag in warm water and look for bubbles coming from the seal - like checking a inner tube for leaks.

A way to check if it is expansion is to submerge the bag in ice water. This will cool everything and if the inflation goes down and the bag looks like it did when you sealed, then it shows that it is thermal expansion not a leak.

[ned]

Very thorough answer. Thanks. So then more specifically. . . I was motivated to buy the food saver because I have been cooking trotters lately and wanting the skin to stay in one piece. There's the old school method with cheese cloth but that seems to me very messy. I had sort of an aha moment thinking that if the feet were in a vacuum bag, the plastic would hold the skin in place. Alas the bag inflated--now I think due to residual air--and the skin split. So I guess the key here is to get a better vacuum. Are there tricks with Food Saver to accomplish that goal? I assume drying everything rigorously is a start. . .

[Shalmanese]

However, there are some scenarios where cooking in a vacuum makes sense:

There is also a very interesting advantage to frying in a vacuum. Acrylamide is a harmful chemical (known to cause cancer) found in fried starchy foods like potato chips. The chemical is increased with high frying temeratures. By putting the cooking under a vacuum you can lower the fry temperature and reduce the amount of acrylamide you generate duing the cooking by up to 90+%.

←

How do you fry in a vacuum? Fried food is putting out an ungodly amount of steam. I imagine it would be a real challenge to maintain pressure in that scenario.

[pounce]

How do you fry in a vacuum? Fried food is putting out an ungodly amount of steam. I imagine it would be a real challenge to maintain pressure in that scenario.

←

I've only seen commercial equipment for vacuum frying. If you do an image search on google you can find a few pics. I assume that if you have a constant draw during cooking you could compensate for the expanding gasses. I imagine that you could rig up a pressure cooker with a high power vacuum pump and try it at home

[nathanm]

I have never seen vacuum frying equipment for restaurant or kitchen use - it might exist, but if so it is pretty exotic. The only vacuum frying equipment I have heard of is for commercial food plants - such as potato chips

Pressurized frying equipment is common - it is used for "broasting" - i.e. frying chicken under pressure. So this equipment is found in lots of kitchens - although usually just fast food places. There is also a manufacturer that makes a home pressure cooker that can do pressure frying.

[jsolomon]

Alas the bag inflated--now I think due to residual air--and the skin split.  So I guess the key here is to get a better vacuum.  Are there tricks with Food Saver to accomplish that goal?  I assume drying everything rigorously is a start. . .

←

Drying will only help so much. You want the food either dry or wet enough that the back does not stick to the foods and can slide around to help the air evacuate.

What temperature were you cooking your trotters at?

[Smithy]

I haven't seen anyone else stagger over this concept, so I must be in need of education. Would someone please 'splain to me what vacuum frying would be? Until now I'd thought that the point of frying was to bring the food in contact with a high-temperature fat in order to cook the food. Done properly, there would be steam driven out and a nice crispy surface produced with little fat impregnating the food. (Done improperly, of course, one gets soggy greasy fries.) The Gastrovac - I'm with you on that name, jsolomon - notes that there's no contact with the fat, and that the cooking is done at lower temperatures. How does this qualify as frying? Someone please enlighten me.

[nathanm]

The gastrovac is just a vacuum chamber.

Vacuum frying means that the chamber is under reduced pressure. There is still oil in it, and the food is in contact with the oil.

Normal atmospheric pressure at sea level is 1 Bar. Water boils at 100C / 212F.

Frying in Denver is actually slightly reduced versus sea level. Frying on Mount Everest would definitely be reduced - pressure there is about 0.3 Bar (one third of normal).

At 0.3 Bar water boils at 70C / 158F.

A gastrovac could presumably do a lower vacuum - probably down to 0.1 bar or less - depends on the pump capacity.

Pressure frying is the same thing but you pressurize the pot above 1 Bar. Most pressure cookers cook at about 2 bar pressure (i.e twice normal). Water boils at a much higher temperature at higher pressure.

The only difference in frying at various pressures is that the lower the ambient pressure, the lower the temperature at which the water in the product will boil. So you could have oil at, say 158F instead of 350F and get a similar effect with respect to dehydration (a key thing for potato chips). However, the lower temperature will NOT brown the food the same way as the higher temp would due to malliard reaction or carmelization.

Note that traditional confit, like duck confit is low temperature frying. The difference between "frying" duck confit in duck fat at 180F for 12 hours at 1 Bar versus doing it at 0.3 Bar at 180F is that the at the low temperature the duck would lose a lot more moisture - it would be above the boiling point. I don't think that this does much for the duck confit, but does have applications to potato chips.