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Flash Freezing with Liquid Nitrogen

Posted by keystone183 (My Page) on
Mon, Apr 25, 11 at 13:53

Been searching for some info on this subject, and can't really find much with respect to food preservation. Here is what i am envisioning.

1. Prep food (veggies, fruit, portions of casseroles, etc.) for freezing put in vacuum seal bags.
2. submerge in container of liquid nitrogen.
3. Place in freezer.

Anyone see any problem with this?? It seems like a great idea, but again, i can't really find anything on it.


Follow-Up Postings:

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RE: Flash Freezing with Liquid Nitrogen

What benefit are you trying to achieve by this?

I'm assuming you already have access to ln2, and have already invested in the storage gear. My concern would be whether the vacuum bags could withstand the ln2 without cracking or deteriorating.


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RE: Flash Freezing with Liquid Nitrogen

I wonder about the benefits too since I have always been under the impression that liquid N is considered a hazardous material to work with - special storage required, special gloves and clothing, special equipment required to apply it, asphyxiation risks, even restricted access to it. Not to mention the expense of it.

I also wonder if it would be immune to the usual freezer problems of auto defrost that ruins so many foods or if it would just be more of the same?

Granted it has role in commercial processing but I can't see a role for it in home food processing based on what I have read about it so far.

Dave


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RE: Flash Freezing with Liquid Nitrogen

The benefits I'm going for here are the general benefits of flash freezing. No large crystallization of the water molecules, thus no mush when thawed? Possibly i have been over sold on flash freezing? I admit i have no experience with it.

As far as the drawbacks mentioned above, none apply (to me). We use it for freeze branding cattle, so i have the dewars already, and it is actually pretty inexpensive. As for the safety risks, as with anything you have to be careful, but so long as you don't contact skin with it, no problems.

I have also been led to believe that the asphyxiation risk it next to nil, N being the majority of the gas you breath and the amount you would typically have to spill to raise that concentration to a lethal level is A LOT. I have no personal experience with that matter, nor do i care to, so it would be done in the garage doors open, where the chest freezer is anyhow.

Basically just wondering if there is anything else here i'm not thinking of. The bag aspect does concern me, but i'm guessing if i don't drop it on the floor and shatter it, it might be ok? Would submerging the vegetable, or meat or whatever directly in the liquid pose any problems?

Probably going to give it a shot, just looking for some input, which i appreciate!


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RE: Flash Freezing with Liquid Nitrogen

I wouldn't be concerned about the food itself. People make ln2 ice cream in their kitchen aid mixes by dumping the ln2 directly in the ice cream base and mixing it until frozen.

Next time you have the ln2 out for cattle branding, why don't you just try a bag or 2 of food and see how it comes out.


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RE: Flash Freezing with Liquid Nitrogen

I think I would freeze the items before packaging for increased surface area with the LN2 and thus faster heat transfer.


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RE: Flash Freezing with Liquid Nitrogen

gotta love innovative thinking! :D


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RE: Flash Freezing with Liquid Nitrogen

  • Posted by skeip 4b / 5a WI (My Page) on
    Sat, Apr 30, 11 at 16:36

If you approach this from the "molecular gastronomy" aspect you may have more luck. Try Howsstuffworks.com and search for flash freezing. It's really not used much for long term storage, but rather for quick and impressive foodie aplications. Good luck.

Steve


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RE: Flash Freezing with Liquid Nitrogen

Ok, a few results. I took some pictures that i will try to post when i get time. I mainly tried this with a few store bought tomatoes just for the sake of experimentation. I started out using a whole tomato. The first one I submerged, i only left in for about 45 seconds. It didn't freeze all the way through. So, the second one, i left in for about a minute and a half. It cracked into about 5 pieces, but was definitely frozen solid (like a rock). Next i cut one in half. About 30 Seconds froze the first half most of the way through. The second half went in for about a minute, and cracked into a couple pieces. On this one i noticed that there was some water/juice that seemed to have been squeezed out of the center and froze in the shape of a water droplet on the inner half. Next, quartered. Only 30 seconds, but again, cracked into pieces. Not sure what is causing them to crack so easily, other than the fact they are about -200 degrees. The real interesting, and important part required a control, so i put a whole tomato in the regular freezer as well. Oh, forgot to mention that all of these tomatoes come out of the fridge, so they were cold to begin with. After freezing all of them, i left them on the counter on paper towels to thaw. It is unbelievable how much frost gathered on the super cold tomatoes. It took about an hour for them to thaw (remember they were all cracked in pieces. The freezer frozen tomato took about 2.25 hrs. The amount of moisture on the paper towels from the flash frozen was about equal to the freezer, but i believe this was due to the enormous amount of frost. The freezer frozen tomato thawed into a mushy ball. Lost its shape actually. The flash frozen tomatoes were actually remarkably similar in consistency to the originals. Not exactly, but close. Thus i would call the experiment a success. Only negative is the pesky cracking phenomenon. Not a big deal though, saves from having to dice them....

I also did some broccoli from the garden, and it seemed to work wonderfully. Didn't thaw it though, straight packaged and to the freezer.


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RE: Flash Freezing with Liquid Nitrogen

Flash freezing depends upon extremely rapid freezing in order to reduce ice crystals to the absolute minimum size.

Speed of freezing is dependent upon the initial temperature, temperature of the cooling fluid and heat transfer rate, which depends upon the heat transfer rate of the food and the distance the heat must travel.

The first process, developed by Birdseye, reduced the distance for heat transfer to a standard distance by packaging things in the same thickness package, running the packages on conveyor belts between metal heat sinks.

This is the same principle as the standard method of ensuring that mixed foods cook at the same speed by cutting things to the same size.

The smaller the pieces, the faster they can be frozen, the smaller the ice crystals, the higher quality the product.

It is probably ideal to bring food down to just above freezing (~30F or -1C) before flash freezing.

Freezing is a mechanical process (though on a molecular basis,) as such it has definite predictable features and time requirements.

Since things freeze from the outside in, you can expect that fluids will accumulate in the middle if the process is slow enough. (This is how freeze-distillation works, the process used to make applejack. It can be used to desalinate and to remove contaminates too.)

Immersion in lN2 has some problems with the mechanical removal of heat--the vapor created by contact with the warmer food items can act to insulate and slow heat transfer.

There is a product on the market called an 'anti-griddle' designed for rapid freezing of sources & such for chefs which operates -30F it is appropriate for freezing fairly thin layers.


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