A question came up in another post about freezing stock. Phil noted that previously frozen food (food frozen in your home refrigerator’s freezer box) looses some quality after thawing and cooking. That being so, how does chicken stock fare after freezing? It’s true, foods do loose a lot of their flavor and texture after freezing. How much depends on what is frozen, how fast it takes to freeze it and how long it is kept frozen.
Without getting too deep into the science of it, what happens is this (we are talking about meat proteins here): As the meat freezes, water crystals form in the muscle fibers. The slower the freezing process, the larger the ice crystals. These large ice crystals are sharp and they poke holes in the meat’s cell walls. When the meat thaws the crystals melt and unplug the holes they made in the cells allowing all the juices to escape. You will often see thawed meat in a puddle of red liquid. This is the meat juices pouring out of the ruptured cells. (Incidentally it is not blood. The protein in blood that turns red when it comes in contact with oxygen is called hemoglobin. The protein in meat juices that also turns red is called myoglobin so don’t get grossed out when you see the red juice; you’re not eating blood!) So, the first thing to suffer is texture. Instead of nice tender meat it becomes dry and spongy.
Another negative effect from freezing meat is rancidity. When the liquid water freezes, the natural salts and trace metals in the meat are brought out of suspension and become concentrated. They react with the meat’s saturated fat and cause it to oxidize and become rancid. And so flavor also suffers from freezing.
The texture thing from ice crystals happens pretty much right away, but the rancidity issue takes some time. Poultry is OK and doesn’t develop any “off” flavors up to about 3 months in a home freezer, while beef should be good up to a year. Pork is somewhere in the middle. I do not recommend freezing fish at all. Aside from the flavor and texture issues, all kinds of other things are going on with fish that makes it smell and taste, well… fishy, in that unpleasant way old fish smells. I only ever buy fish the day I am going to use it (or at the most, late in the day before) and keep it on ice/refrigerated till the last minute.
Bacteria that contribute to meat spoilage need water to be active. When the water in the meat is frozen, biological processes are halted. In the frozen state meat will remain unspoiled pretty much indefinitely. Would you want to eat it after 1000 years? Probably not!
So then, what happens to chicken stock when you freeze it? Nothing much. There are no cell walls to rupture with ice crystals and it is virtually fat free so rancidity is not a problem either. I have used 6 month old frozen stock that tastes just as good as the day I made it.
Commercial enterprises flash freeze their products. In the home freezer it can take some hours to completely freeze a lump of meat, thereby producing large, destructive ice crystals. Commercial equipment freezes the product in seconds rather than hours. The ice crystals formed are very small by comparison and therefore less destructive.
What about freezing fruits and veggies then? Bad idea!
Remember that ice crystal thing in meat? Well, it does a real number on delicate vegetable cells, turning them to mush. You can buy the frozen fruits and veg at the grocery store which have been flash frozen but thawed, they do not retain their original form or texture. They are always a bit mushy and less intensely flavored.
Refrigeration, although not as severe as freezing, can also negatively impacts some foods if you are not careful.
The fridge is the ideal place for short term storage of meat, butter, cheese, etc. But when it comes to fruit and veg, well, that’s a different story.
Produce native to temperate climates can tolerate the cooler temperature of the fridge and will, in fact, keep longer. Produce from tropical or sub-tropical climates do not do well in the fridge and keep longer at room temperature. Delicate cell walls are damaged by uncontrolled enzyme activity at cooler temperatures and flavor suffers. Whenever I see tomatoes in someone’s fridge, I always try to persuade them to keep them on the counter at room temperature.
Onions are an odd one. Fresh onions picked out of the ground are very perishable and need to be refrigerated. I don’t know if onions are native to cooler climates but they certainly grow well there. Onion producers take the newly harvested onions and put them in a heated room to dry out the surface layers and develop that papery skin we typically see. This makes the onions shelf stable for longer at room temperature. A cut onion will dry out in a day on the counter, even wrapped in plastic wrap. Double wrapped in plastic (to prevent the onion smell from contaminating other food) a cut onion will keep a week or more in the fridge.
Another question that often crops up is, “Is it safe to re-freeze food once it has been thawed?”
I have heard two different answers to that: One is, if you can eat it you can freeze it, keeping in mind the texture flavor problems will be more pronounced. The other answer is, no, it is not safe to re-freeze food that has been previously frozen and thawed.
My own feeling on the subject (and this is just my unscientific opinion) is that the first answer is probably correct provided the food has been properly handled while thawed. From a food safety point of view, the second response is the correct one. I guess the best response I have is, “If in doubt, don’t”. And anyway, if the taste and texture are going to suffer even more after a second freezing, why would you?
kaysdad
