What is the purpose of "shock chilling" food after cooking?

Question

Recipes often have instructions like:

Remove bag from bath and immediately transfer to an ice water bath to shock chill the turkey.
— (The Foolproof Sous Vide Thanksgiving Turkey).

I never see them giving any reason for doing this though.

Sometimes it's done before putting it into the refrigerator or freezer, and sometimes (as in the above example) it's before browning it in the oven.

What exactly is the purpose of "shock chill", and in particular, what happens if it isn't done?

Note: I can understand needing quick cooling to prevent over-cooking, but in this case the method is sous vide, so that isn't a concern. Nor is bacterial growth.

Answer 1

Even with sous vide, both overcooking and bacteria can still be a concern.

In this case, it's about over-cooking. Consider the meat just under the skin you want to brown. If it starts at the ideal cooking temperature, by the time the skin is nicely browned in the oven, it will be overcooked. By cooling it first the oven reheats it rather than overcooking it. It's probably quite a thin layer that would overcook, but avoiding dry meat just under the skin is presumably why you're cooking it sous-vide in the first place.

Chilling in cold water (ideally quickly) before putting it in the fridge or freezer reduces the amount the fridge warms up, protecting the rest of your food from loss of quality (or even spoilage if you put lots of hot stuff in there).

Sous vide temperatures usually aren't enough to kill all bacteria, so even in a sealed container some can start regrowing if it sits around warm for a while. Rapid chilling avoids that, especially for whole cuts of meats where the surface is the highest risk. Then you can carry one cooling in the fridge if you're storing.

Answer 2

It is done to bring carry-over cooking to a halt. Lots of sea cockroaches need to be boiled at high tempratures for just a couple of minutes.

If you let it be carry-over cooking will turn it into rubber.

If you dump it into cold water it will stop cooking altogether and it will be cooked perfectly.

If you take food out of the oven and keep the vessel closed the food will happily keep on cooking for 20 more minutes.

For a lot of food this is ok, but for certain foods that have a small window of correct doneness this needs to be prevented.