This article is from the Food Preserving FAQ, by Eric Decker email@example.com with numerous contributions by others.
Freezing is preserving food using low temperatures--generally at
temperatures around 0 F/-18 C. Freezing generally inhibits both microbial
growth (doesn't generally kill, though) and many protease/enzyme actions
in the food itself.
You need to decide whether or not to blanch or process food, how to wrap
food to prevent freezer burn, what foods freeze well, and what to do when
the power goes out.
Food is safe from spoilage AS LONG AS IT STAYS FROZEN. Microorganisms
can start to grow as soon as food begins to thaw. To keep microbial growth
at a minimum, frozen foods should be thawed in the refrigerator. Thawed
food may be refrozen IF ICE CRYSTALS ARE STILL PRESENT IN THE FOOD.
Refreezing often changes the quality of food (texture, color, flavor).
Foodborne illness causing microorganisms may not be killed by freezing,
so the safety of the food will be no better than the condition of the
food which was frozen.
(section taken from Susan Brewer, from cesgopher.ag.uiuc.edu). [Symptoms
of food poisoning are discussed in Section IV. Spoilage--LEB