Frozen

Freezing happens when the temperature of a (food/drink-)item reaches sub-zero degrees celsius or sub-32 degrees fahrenheit. (frozen) food items will spoil slower.

Outdoor freezing can be caused by cold weather.

There are several ways to thaw food, you can increase the ambient temperature with a fire, or place the food in a different Z-level which has higher temperature. (Often cellars are cold not freezing).

You can also use a tool with the "food cooking" quality, such as a hotplate, or even a pot or pan if there is a nearby fire to de-thaw your food. You can also heat the food up to being (hot), which usually improves the morale bonus from the food, if you don't get a morale bonus by heating this food, there is an option to stop heating after thawing the food.

Frozen liquids can still be unloaded from one container to another, even if it is toilet water you can still examine the toilet to pour the frozen water into a suitable container, no need to wait for it to thaw.