It is generally not recommended to refreeze a previously frozen pizza that has thawed in the refrigerator for several hours. When food is frozen, ice crystals form inside the cells of the food. Thawing and refreezing can cause these ice crystals to melt and refreeze, leading to changes in the food's texture, taste, and potentially compromising its safety.
When a pizza becomes soft and soggy due to thawing, it's likely that the moisture from the frozen pizza has condensed and created excess moisture on the surface. Refreezing this pizza may further degrade its quality, resulting in a less-than-ideal texture and taste.
Moreover, refreezing potentially hazardous foods, like pizza with meat or dairy toppings, can increase the risk of bacterial growth and foodborne illnesses. When food is kept in the "temperature danger zone" (between 40°F and 140°F or 4°C and 60°C), bacteria can multiply rapidly, causing potential health risks if consumed.
If you find that your pizza has become soggy and difficult to detach from the cardboard tray, it's best to consume it promptly or cook it in the oven as soon as possible to minimize the risk of foodborne illnesses. Cooking the pizza will also help restore some of its texture and flavor.
To prevent this situation in the future, it's a good idea to portion and freeze your pizza slices separately in airtight containers or freezer bags. This way, you can take out only the number of slices you plan to eat, reducing the need to refreeze the entire pizza.