Freezing and thawing food industry items -- how to do it the fastest....

[Tonyor]

Hi, I need to find out about the length of time it takes to change from one state of matter to another. This is a food industry problem. For example, how long does it take to freeze a leg of lamb? Does the time it takes depend and anything in particular?

Going the other way we can speed up the time it takes to thaw a frozen leg of lamb by throwing more energy at it. However, my question is asking if there is a way of speeding up the freezing process and if there is, is there any kind of ceiling which denotes the fastest way a leg of lamb can be frozen? Is there a barrier which we cannot get past or will we be able to continue to increase freezing speeds in future?

Sorry for all the questions.

Thanks,

Tony :)

 

[berkeman]

Welcome to the PF.

For thawing, it's hard to beat a microwave oven on the "Thaw" setting.

For freezing, I would think you need to respect the cellular integrity of the food product. You can drop it in a container of liquid Nitrogen, and it will "freeze" in a couple of seconds, but I doubt that the meat would be worth much even with careful thawing.

You speed up the "freezing" process by increasing the thermal conductivity of the media surrounding the food product to be frozen. But I would think that if the thermal gradient were too steep spatially, you could get some cellular damage that would also ruin the meat.

Maybe that's the limiting factor that you are thinking about. But if so, you would need to look into how meat freezes, and how to preserve the cell structure of the meat as the freezing progresses through the body of the meat, IMO.

 

[phinds]

What research have you done so far? What have you found out?

 

[Tonyor]

Thanks for the info. I have not conducted any research so far, except for this forum question. I understand that some kinds of freezing could cause cellular damage but what if it were possible to freeze it extremely quickly. If it could happen fast enough, there would not be enough time for ice crystals to cause any damage. Is there any way that instant freezing can be achieved?

 

[berkeman]

Sure, just use liquid Nitrogen. Then slowly thaw it and cook it and see how it tastes. Maybe you could be onto something!

 

[Tonyor]

I think you were right when you said that after a dip in liquid nitrogen the meat would not be worth much. I'm wondering if there is any way to freeze it even quicker though? Any ideas?

And can I ask why you suggested it should be thawed slowly? How would thawing it quickly affect it?

Thanks,

Tony

 

[Evo]

Are you talking about the industry standard of "flash freezing"?

https://en.wikipedia.org/wiki/Flash_freezing

 

[BillTre]

Here is an extreme example of fast freezing while maintaining the natural ultrastructure (anatomy at the molecular level).
Now ancient neurobiological research used extremely fast freezing times to study how neurotransmitter vesicles fused with the cell membrane in electron microscopy (EM).
They used a series of tricks to do this:

• They had a nerve-muscle prep wired up to stimulate the prep at the proper time to catch the vesicles in the act of fusing to the cell membrane in response to the neural stimulation.
• The prep was cooled to as close to freezing as possible while still getting neurotransmission.
  
• At a proper time with respect to when the prep was stimulated it was mechanically slammed onto a block of metal (probably copper, good heat conduction) that was temp equilibrated with liquid helium (colder but more expensive than liquid nitrogen).
  
• The prep is physically very thin (a few microns) making it easy to freeze it quickly. Large objects have trouble conducting heat out of their interiors with any speed. The outsides shrink and then crack around the unshrunken unfrozen interiors. this can happen when you throw something into liquid nitrogen.

This resulted in extremely fast freezing, which forming non-crystalline (amorphous) ice containing the cellular components which were then fractured and viewed in EM. No crystals are formed, which is optimal, but the process involves lots of destruction of parts of the cellular structure. I doubt they have been tasted.

This is probably the gold standard of fast freezing, but is really limited to very small things. Seems to me that this should also be the best way to preserve food, but the volumes are too small to be useful. Adaptations would have to be made for larger things, like:

• Use as small pieces as possible (or maybe drill holes or drive pieces of conductive metal through it)
  
• Bring close to freezing
• Freeze quickly

Not sure if cracks would affect taste, but it would look strange. The big limitation will be removing the heat from the interior of a large thing frozen on the outside.

Thawing larger things with a microwave sounds like a good idea since it should penetrate well. Otherwise soak in warm water.

Freezing cells so that they can be brought back after being thawed usually involves:

• soaking cells in cryo-protective chemicals (probably not tasty)
• start with the cells close to freezing temps
• freeze at particular rates that depend on what is being frozen (something like one degree C/second.
  
• thawing is usually done rapidly (throw the 1 ml vial into a water bath of the temperature the cells are normally at) and then remove the cells from the freezing chemicals (by centrifugal)

Storing frozen cells at -80˚C or warmer will cause the largest ice crystals present in the frozen sample to get larger (at the expense of smaller ice crystals in the sample) and compromise cellular integrity. I expect this would also to affect food. Therefore, store in liquid nitrogen (LN).

This is also quite different from chunks of food.

Ice creme making works very well with LN (watch out for contaminants though). Just pour it in with the components and stir till frozen. Very fast.

 

[Tonyor]

Thanks everyone. The Flash Freezing link is very useful as is all the info you've given me. I'll try making the ice cream too!

Much appreciated,

Tony