Thawing cryovac-ed fish

[Dianabanana]

Whenever I buy frozen fish, it's in cryovac packaging (at least I think that's what you call it--the thick plastic, sort of like shrink wrap). The instructions on the bag say to remove it from all packaging before thawing, and then the cryovac plastic has the same instruction emblazoned across it, as if it's v. v. important. But why? I thawed some halibut last night without taking it out of the plastic first and I can't tell the difference.

[John DePaula]

I noticed that, too, and like you, I've never noticed any difference either way.

I assumed that it was potentially a "crush" problem: as the fish thaws, it can't stand up to the vacuum (the cells implode?) so texture is adversely affected.

[nickrey]

Considering that those of us who cook fish sous vide do so in "cryovacced" plastic for exceptional results, this seems counterintuitive to say the least.

[BeeZee]

I noticed that, too, and like you, I've never noticed any difference either way.

I assumed that it was potentially a "crush" problem: as the fish thaws, it can't stand up to the vacuum (the cells implode?) so texture is adversely affected.

Makes sense since I've seen the instruction to open the bag (break the seal) to defrost, also.

[Blether]

It is wierd, but my guess is it comes out of the world of microwave defrosting and is a short form of something like

HOW CAN I DEFROST FROZEN FOODS USING A MICROWAVE?

When defrosting packaged store-bought foods, check the label for microwave defrosting instructions. For foods with no instructions provided, remove food from its packaging before defrosting and place in a microwave-safe container, covered with a lid or plastic wrap, as discussed above. Refer to the microwave user manual, if available. If not, select the “defrost” setting or 30 percent power and set the time according to the size and amount of food to defrost. Without specific guidance, it is a good idea to test the progress by using a knife or fork to pierce the food and feel for frozen spots every minute or so until the food is completely defrosted. Also, while defrosting, rotate, stir or turn food upside down where possible, and for individual pieces, such as chicken parts, break them apart. When thawing ground meats, as the meat softens, scrape it from the frozen mass and remove it from the oven. Continue this process, as often as necessary, to properly thaw the meat.

Cook meat, poultry, egg-containing dishes, and fish immediately after defrosting. Hold or store these foods at refrigeration temperatures (less than 41° F; 5° C) to prohibit the growth of hazardous bacteria, which may cause illness even if the food is cooked thoroughly at a later time.

From microwaveovenfacts.com.

Metallic packaging's a prob, of course, and I've noticed some labels aren't inert to microwave application.

Edited March 27, 2010 by Blether (log)

[RobertCollins]

I wonder if the heat will or would cause some sort of off gassing?

Like BPA when you heat up baby bottles. [ I read something about that. My babys bottle days were still all glass.]

[ray goud]

They say that because they assume we are all dimwits and will defrost at high power, causing a sudden increase of pressure inside the package. I have consistently ignored the warning and defrost without even piercing the packaging, without ANY problems, because I defrost at reduced power.

Ray

[Porthos]

When I defrost cryovac-ed packages I don't open the package and I use the 10% power setting on my microwave. Works like a charm. You just have to remember to start the process soon enough to use the gentle heat for defrosting. Otherwise all bets are off.

[nickrey]

Why defrost in the microwave? The package is sealed so you can just put it in some warm water. The water conducts the heat much better than air and will defrost it before you know it.

Edited March 28, 2010 by nickrey (log)

[Blether]

Why defrost in the microwave?

Faster / more convenient, IME. Chunk of ginger, 1" x 2", for example - about a minute or a minute and a half, and it's soft enough all the way through for easy chopping, and my machine has an auto-sensor for the defrost function just as it has for 'heat up'. Haven't tried hot water on that specific one. I'm not keen, myself, on microwave defrosting for uneven things like fish, or poultry bits, because of the way it'll cook in parts if you turn your back for an instant.

Edited March 28, 2010 by Blether (log)

[Shalmanese]

Exactly, cryovac in warm water is maybe 3 minutes slower than a microwave but you don't end up with icky cooked pieces of fish.

[PedroG]

I suppose that the fish is frozen before being cryovacced. In the frozen state, a 99.9% vacuum of a professional chamber vacuum machine will not affect the texture of the fish, but as soon as it is thawed, this high vacuum may compress it and deteriorate the texture (cf. post #2). So it would be better to transfer the fish to a Ziploc bag (or Foodsaver bag, but with minimal vacuum) together with your preferred ingredients. For cooking sous vide, it is not necessary to thaw the fish first, just drop it in the water bath, and use the old rule of thumb "increase the cooking time by 50% when cooking from frozen", as Douglas Baldwin provided cooking time tables for thawed fish only in his Practical Guide http://amath.colorado.edu/~baldwind/sous-vide.html

Chicken texture changes dramatically as the amount of vacuum is increased. In every case, the oil packed chicken was preferred to the no-oil chicken because it had a better mouth feel. By far, the 90% vacuum chicken was the best. As the vacuum level increased, the chicken oddly became wetter, but with a drier finish in the mouth after chewing, and seemed mushy. The 99% had a particularly bad texture, mushy but not moist. The 99.9%+ was the most overall unpleasant, because of the overly wet meat with the dry finish in the mouth. Bizarre.

Fish is even more dramatic. We all preferred the 90% fish in oil. The 99.9%+15 seconds was inedible and mushycompletely useless. Just like the high vacuum chicken it starts too wet and ends dry. There was a big difference between 90% and 98%, a medium difference between 98% and 99%, and a big difference between 99% and 99.9%. Lower vacuum was better in every case. In the picture of the cut-up fish you can see the difference in texture. We put some pieces in a dissecting microscope to show the structure of the fibers and you can see the 90% fish has much better structure. The 99.9%+ fish is wet, but the fibers dont look right.

http://www.cookingissues.com/2009/06/17/boring-but-useful-technical-post-vacuum-machines-affect-the-texture-of-your-meat/

[nickrey]

I suppose that the fish is frozen before being cryovacced. In the frozen state, a 99.9% vacuum of a professional chamber vacuum machine will not affect the texture of the fish, but as soon as it is thawed, this high vacuum may compress it and deteriorate the texture (cf. post #2).

I'm not sure if that would happen Pedro.

The frozen state of water is larger than its thawed state so we can surmise that the frozen fish will be expanded beyond its normal size and vacuumed in that state. Given this, as the fish thaws it is likely to shrink somewhat. It is therefore possible that the vacuum will not be as strong on the reduced sized and now-thawed fish.

Definitely worth an experiment to see if it affects texture.

[mtigges]

In my experience it's so that the fish doesn't lie around in it's own goo. I eat a lot of fish that I catch and vac-pac for freezing myself. There is always a little bit of viscous gooey liquid that in my experience, it's best to have run off while defrosting. I take it out, put it in a large stainless bowl over a little rack, and the excess liquid drips off. If I fail to do that and defrost in the bag, the odor is a bit fishy. A rinse solves that though.

Perhaps commercially vac-pac'd fish is processed a little more thoroughly than my filet, rinse, bag 10 min job though.

M

[abooja]

I defrost cryovac-ed fish by placing the still-sealed fillets in between two nested 12" cast iron skillets. I never run the risk of cooked fish bits and can attend to other tasks while the fish defrosts. Thin fillets are defrosted in around thirty minutes.

[PedroG]

I suppose that the fish is frozen before being cryovacced. In the frozen state, a 99.9% vacuum of a professional chamber vacuum machine will not affect the texture of the fish, but as soon as it is thawed, this high vacuum may compress it and deteriorate the texture (cf. post #2).

I'm not sure if that would happen Pedro.

The frozen state of water is larger than its thawed state so we can surmise that the frozen fish will be expanded beyond its normal size and vacuumed in that state. Given this, as the fish thaws it is likely to shrink somewhat. It is therefore possible that the vacuum will not be as strong on the reduced sized and now-thawed fish.

Definitely worth an experiment to see if it affects texture.

Density of water is

• 0.99987 at 0°C
  
• 1.00000 at 3.98°C
  
• 0.99025 at 45°C
  

i.e. from 0°C to 45°C there is about a 1% expansion.

I agree it would be worth an experiment (Dave Arnold??).

[Paul Kierstead]

The density of ice (water in its frozen state...) is around 0.917.

Of course, was the fish flash frozen and then packed, or packed and frozen? Likely the former to prevent damage.

[nickrey]

The density of ice (water in its frozen state...) is around 0.917.

Of course, was the fish flash frozen and then packed, or packed and frozen? Likely the former to prevent damage.

If my memory serves me correctly, if you freeze 10 units of water, you get 11 units of ice, ie. there is a 10% expansion on freezing.

This leaves a lot of room for the vacuum to be mitigated as the fish thaws as long as it was either frozen before being packed or packed at the appropriate vaccuum for fish and then frozen.

[James Schroeder]

I ran across this explanation from a company that sells seafood:

....products are sealed in vacuum-packed pouches while still frozen. This prevents dehydration or “freezer burn”, and is most effective way to preserve quality. We go to great lengths to bring you the best seafood possible, as with any all-natural product there are bacteria that develop during the thaw process. The curious thing about seafood is that when in an anaerobic (airless) environment, there is a chance of the formation of the bacteria Clostridium botulinum, also known as C-bot, a cause of food poisoning. By removing the packaging, you eliminate the risk of C-bot contamination. Just to be on the safe side, the FDA requires these guidelines for all vacuum-packed seafood.

[nickrey]

Welcome to eGullet James.

This is highly unlikely to happen with any of the accelerated processes we have discussed here. It has the potential to do so, however, if you leave the package to thaw on the bench top. It seems that the guidelines are there to protect the lowest common denominator, which is a good thing for guidelines to do.

Edited August 5, 2012 by nickrey (log)