Large ice clumps may indicate thawing and refreezing, but appearance cannot establish safety. Do not eat the food if you do not know how long it was warm; refreezing does not undo unsafe storage.
Some ice inside a frozen package is expected. Moisture on the food’s surface passes into the air inside the package and collects on the inner surface as a thin layer of frost. This frost is powder-fine, evenly distributed, and crumbles when rubbed by hand. There is no problem with a package like this; it only indicates that the package contains some air and that freezer drying may begin over time. What matters is not whether ice is present, but its form: fine frost and hard ice tell different stories.
The problematic appearance is different and easy to recognize: a hard, clear slab of ice in a corner or at the bottom of the package; large clumps lodged between pieces and frozen into one mass; or individual foods such as peas and corn stuck together in a block. Hard, clear ice is different from frost because the frost has melted into water and then refrozen. This means the package began to thaw at some point and then froze again. Meltwater flowing to the bottom of the package and freezing there is evidence of the same cycle.
There are several possible explanations for why this cycle happened. The product may have warmed up on the way home from the store; the freezer door may have been left open for a long time or not closed completely; there may have been a power outage; or the package may have sat for months in the most temperature-variable part of the freezer, on the door shelf. Regular defrost cycles in a frost-free freezer can leave a similar sign over time, but the ice formed there is usually thinner and more scattered. The cause often cannot be known; what you can read is the result, not the cause.
The decision when you see this sign depends on two questions. Is the product still completely frozen and hard? Has any part softened or warmed, or is there liquid water inside the package? If it is still completely frozen and hard, it is safe and can be used; because its texture and flavor have deteriorated, set it aside for a cooked dish rather than eating it raw or using it in a recipe where appearance matters. If part of the product has softened or warmed, or there is liquid water inside the package, the decision changes: do not use raw meat, chicken, fish, or cooked dishes in this condition. For foods such as bread, pastries, and vegetables, the only problem is texture loss.
You can also read the same sign while shopping, and it can save you money. If you see large ice clumps in a package in the store freezer, put that package back on the shelf because it indicates that the cold chain was broken somewhere. At home, prevention depends on where you place the package: put foods that will be stored for a long time in lower compartments away from the door; make sure the door closes fully; and wipe the seal regularly. Clear bags make it easier to check the contents because you do not have to open the package to look inside, and every opening allows new moisture in.