When slacking frozen food, if pulling out food needed from the bunch, can the remainder be returned to the freezer?
– Josie Jennings, Owner, Learn About Food, Belleview, Fla.
Slacking, as defined by the FDA Food Code, is, “… the process of moderating the temperature of a food such as allowing a food to gradually increase from a temperature of -23oC (-10oF) to -4oC (25oF) in preparation for deep-fat frying or to facilitate even heat penetration during the cooking of previously block-frozen food such as shrimp.” Slacking is typically—and most safely—done by moving frozen food to a refrigerator under 40 F to allow it to slowly and safely come up to temperature before cooking.
Your question is a good case of distinguishing between what should be done and what can be done.
As a kitchen best practice, all of the food slacked should be cooked to a safe internal temperature and served following the slacking. None should be returned to the freezer. Variations in temperature caused by slacking and refreezing could reduce shelf life, impact food quality by changing textures and moisture content (causing sogginess in breaded items, for example), and, from a food safety perspective, can introduce some risk of microbial growth or contamination. In short, it is best to keep frozen foods frozen until ready to use.
That said, if the slacked food remains frozen and has been kept free from time-temperature abuse, it can be returned to deep freeze at a colder temperature and still be compliant with most health codes.
To avoid this problem, it is best, if possible, to adjust batch cooking size to common pack sizes for frozen food. To use the FDA’s example above, if a recipe calls for 4 pounds of shrimp, converting it to require the standard 5-pound block would make much more sense if it could work from a business standpoint. Further, breaking up cases at delivery to freeze them in more logical portions for slacking may help.
More on freezing—and refreezing—here.