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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.

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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.

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  • "Sous vide temperatures usually aren't enough to kill all bacteria". Generally they are enough when combined with long times. But in this case the temperature is 165°F, which is enough to kill it in a few seconds, so 6 hours should definitely do the job.
    – Ray Butterworth
    Dec 6, 2022 at 16:50
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    @RayButterworth for turkey yes, it needs to be. Beef less so
    – Chris H
    Dec 6, 2022 at 16:56
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    @RayButterworth Sous vide is generally considered a pasteurization method, not a sterilization method, so it doesn't kill all bacteria and can even induce spore formation in some species, which will then resume multiplying quite happily once back to more normal temps. The quick chill limits the potential for further growth from being in the growth range while cooling at room temp. Note that bacteria that are resistant to 165F are resistant no matter the duration of this temp...
    – bob1
    Dec 7, 2022 at 3:32
  • Yes, in this case it was entirely about keeping the overcooked outer layer as thin as possible. I did notice that the very thin parts were not as tender as the rest. Next time I'll take the time to fully refrigerate it before doing the browning.
    – Ray Butterworth
    Dec 8, 2022 at 2:05
  • I'm not sure about fully refrigerating before browning. Then it would be cold inside, and it shouldn't be in the oven long enough for much heat to soak in. There's probably a fairly fine balance to be struck between cooling the outside enough and not cooling the inside too much. This will be helped by a hot oven and moving quickly from chilling to browning so the outside doesn't rewarm from the heat still in the bulk of the meat
    – Chris H
    Dec 8, 2022 at 6:34
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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.

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  • In this case though, with sous vide cooking, the meat is entirely and uniformly at the right temperature. It will cool off from the outside in, but none of it will get any hotter or cook any further. Even if there were any carry-over, the effect would be far less than if the meat were simply cooked for an extra half hour , and with sous vide even an extra hour or more seldom makes any difference.
    – Ray Butterworth
    Dec 8, 2022 at 2:03

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