Ice crystals on frozen foods?
I purchased a package of frozen salmon with "Mojito" sauce from TJ's about 3 weeks ago. It has been in the freezer since, and been stored at a pretty even 0 degrees F. Looking at the package today, I notice that the fish is covered with snowy ice crystals. What has caused this...and is it ok to eat the fish, or should I toss it?
Pre-packaged frozen foods will form ice crystals rapidly if they were allowed to partially thaw and re-freeze. Always watch for this at the frozen food section of your grocery store. Sometimes a bag or box is taken out and left somewhere then put right back in the freezer. Sometimes it takes a long time to get from the truck to the freezer.
Carefully inspect your frozen food before purchasing. Don't buy it if it already has ice crystals or if the bag has some pieces loose and the others clumped. That is a sure sign that it was refrozen.
Todao is right about the vacuum sealed bags too. Also, keep in mind that nothing seals forever. A properly vacuum sealed bag may well have let atmosphere in over a year in the freezer and that leads to freezer burn. So, try to rotate your frozen goods out of the freezer in 6 months or so.
"What has caused this ..."
Ice crystals form on frozen foods that are packaged in containers that contain air (are not vacuum sealed) and/or those that are packaged in wrappers that do not keep them air tight. Even plastic wraps, depending on their quality, will leak some air. Air contains moisture/moisture breeds ice crystals and generates freezer burn. A quality freezer bag from which all the air has been purged will keep frozen foods relatively free of ice crystals for a longer period of time.
the question of quality versus safety are different.
Safety? totally safe to eat and it will not make you sick.
Quality? It has been compromised. Visible chunky ice crystals, versus a smooth layer of ice on the surface, is a sure sign that the food in question has the temp has, at one point in its life, gone above 32 degrees under incorrect storage conditions, and been refrozen under correct conditions.
It is totally safe to eat, but the taste and quality has been compromised a teeny bit.