FREEZING & THAWING
An American, Clarence Birdseye, was working in Canada as a fur trader when he noticed when fish are frozen very quickly, they remain in perfect condition or months. By 1924, (exactly a century ago as I write this), Birdseye had created the frozen food industry. The secret was FAST freezing, to get the water in the cells of the meat or fish or plants frozen as very small ice crystals. Slow freezing (as we do in the home freezer) creates large ice crystals that break the cell wall and allow fluids to leak out during thawing.
Freezing is not a reliable way to kill bacteria, but it is effective in destroying a number of parasites in foods. For this reason, raw fish, selected for sashimi, is invariably frozen during transport (outside of Japan). This preserves the freshness and quality of the fish and also kills any parasites. Much of the harvest of modern commercial fishery vessels is processed and frozen on board.
Meat is not rendered 'safer' by being frozen. If it has begun to decay when it goes into the freezer if will resume decaying as soon as it is thawed. But reducing the temperature to -18 C (0 F) will preserve the food from bacterial growth indefinitely. Certain chemical changes still continue under freezing conditions although more slowly. For example, poultry fats (turkey, duck, chicken) still continue to oxidize (acquire a rancid taste) while frozen. The fat of oily fish (e.g. herring, salmon, trout, mackerel) will become amber in colour after a few months. Try to keep poultry (especially raw turkey) to maximum 6-8 months frozen storage, and storage in airtight "vacuum" pack will prevent oxidation. Physical changes can also be expected when food is left exposed during frozen storage. "Freezer-burn" has nothing to do with burning but is instead is a freeze-drying process. Water in the tissues is lost by 'sublimation', meaning that the water changes from solid to vapour without going through a liquid phase. The fish, meat, or baked goods become dry and fibrous. Prevention is by wrapping tightly, preferably in a 'Cryovac' or other vacuum packaging system.
Q: What is the best way to thaw meat in a hurry? I heard you shouldn't use warm water
Q: Many people say you cannot re-freeze raw meat why?
Q: If ground meat was previously frozen, what will happen if I freeze it again?
Q: What is freeze-dried food and can I make it at home for camping, etc.?
Q: What is the best way to thaw RAW meat in a hurry? I heard you shouldn't use warm water
A: If you have the foresight, thaw the meat in a refrigerator overnight. But if in a hurry, there's nothing wrong with thawing it in a tub of water, even warm-ish water to accelerate the process. Try to limit this activity to water-tight bagged - or vacuum-packaged - meat or poultry, to reduce the risk of contaminating everything in the kitchen with Salmonella or E. coli bacteria. That's the real risk with raw meat. Having the meat warm for a few hours in a warm room or warm water will not create any unsafe conditions; the meat will be cooked afterwards.
Q: Many people say you cannot re-freeze raw meat why?
A: You can re-freeze meats any number of times, without producing a health or safety issue. Freezing is a mechanical temperature-drop that suspends all bacterial activity, which then resumes when the meat is thawed. There is often a ‘quality’ loss (appearance, weight, texture, colour) with 'slow' freezing (as in a home freezer), but this is nothing unsafe. When the meat is thawed, it is fine to use or re-freeze. The REAL problem arises from how long the meat has been thawed, and at what temperature? For instance, a food inspector or health inspector would be suspicious if food was delivered to a store or kitchen showing signs of having been thawed because if may have been in a truck for days during the summer with the "reefer" unit broken or turned off (It has happened!). That's where the myth started. But if you are home KNOW that the food was thawed a day ago and is still fairly cool, and has not been heated, then you are fine refreezing the meat.
Treat previously frozen meat the same as fresh meat. Examine for colour changing to greeninsh, a surface slime, or a sour smell. If it passes these tests, go ahead; it cannot hurt you (but still be extremely cautious about not cross-contaminating other foods or equipment before it is cooked. That's where the danger lies.
No foodborne illness has ever been attributed simply to refreezing RAW meat or keeping RAW meat at room temperature for a day or two before cooking.
Q: If ground meat was previously frozen, what will happen if I freeze it again?
Ground meat, whether previously frozen or not, has a limited life in your fridge before it becomes unpleasant. The bacterial load is high because it has been made from all the off-cuts and trimmings, and that's where the bacteria live. So you can expect colour changes within hours, but let your nose be your main guide. Can you smell a pronounced sour odour? It can even be quite objectionable. That's the time to dump it because it would not be pleasant to eat.
But if it hasn't developed surface slime, or unpleasant odours, even if the colour has changed to grey at the centre or brown on the outside (oxidation/reduction effects), then you are ok to cook it (all through to at least 72C / 160F ! ).
Q: What is freeze-dried food and can I make it at home for camping, etc.?
Freeze-dried foods were developed originally for military purposes, space missions, and more recently camping and survival food supplies. These cannot be made at home without extensive and expensive equipment.
The food is prepared and cooked to the point of being ready to consume, and then frozen solid. The blocks of frozen food are placed in a vacuum chamber, and the atmosphere reduced considerably. The temperature is increased which allows the water to sublimate (pass from solid to vapour without passing through the liquid phase. The result after same hours, is the same block of food without the water. It's extremely light in weight and can be packaged, crumbled in airtight pouches often using nitrogen to prevent oxidation of the fats. The shelf live can be for years.