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In a world I am creating, some people have colonized Ceres-like and Moon-like worlds - that is, they live in domes or underground, in pressurized buildings. The planets have no atmosphere for all practical purposes.

I am now working on such people's cultures, and I'm considering food. Would it be possible to use the vacuum of space to prepare, or at least conserve food?

What I imagine is exposing vegetables to the vacuum of space to dehydrate and freeze them at the same time. One could expose milk to vacuum to remove its water content and get condensed milk. Airlocks could double as cattle slaughtering devices - kill and freeze the meat in one go.

I'm also thinking that all that UV could help kill microbes, if the cold didn't already. Otherwise if radioactivity is an issue, food could be exposed to vacuum underground or in the shade of a hill or mountain.

Would this be feasible, or is it just another ignobel waiting for us to colonize space before it happens?

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    $\begingroup$ Possibly of interest to you worldbuilding.stackexchange.com/q/90815/40408 $\endgroup$
    – Ash
    Oct 2, 2018 at 17:21
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    $\begingroup$ You don't want to kill animals with Airlocks. I've heard that if an animal dies with suffering its meats becomes hard and ugly. That is why we kill them instantly and painless. $\endgroup$
    – Ender Look
    Oct 2, 2018 at 17:22
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    $\begingroup$ @Renan, seafood is very different than other kinds of foods. I'm talking more about cows, cattle, etc... mammals, not fish. $\endgroup$
    – Ender Look
    Oct 2, 2018 at 18:16
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    $\begingroup$ @EnderLook, you really should look much further into slaughtering techniques. I'm an unrepentant meat-eater, but I'm under no illusions about how that industry works. $\endgroup$
    – user8827
    Oct 3, 2018 at 18:01
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    $\begingroup$ It takes quite a while for an animal to die by exposure to vacuum more than enough time for them to panic, especially compared to something like a bolt gun, I can't see a society supporting far crueler execution methods. $\endgroup$
    – John
    Oct 4, 2018 at 13:30

3 Answers 3

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@L.Dutch pointed out why direct vacuum would not be a good idea but there is a way of using space vacuum indirectly.

  1. Cut the meat or vegetables into "use size" pieces. This makes the
    cooling faster and allows you to heat smaller portions at one time.
  2. Place between racks that are attached to shaded radiators. This will allow conduction cooling which is much faster.
  3. Then use a bladder exposed to vacuum to pull the air from the chamber. That way, you don't lose the air or moisture.

Once the vacuum and cold have done their work, you can tilt the racks to dump the food into packages. After you seal the packages, compress the bladder, collect the condensed water, open the door and take out the dried and vacuum packed food.

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Considering that in space water is scarce, letting all the water from any food escape in the big big big emptiness sounds like a really poor idea. So, definitely a no no for vacuum dehydration.

Simple freezing by exposure to void seems also like an overkill: thawing an half ox for lunch would require a large amount of energy, and energy, guess what, is also scarce in space! In this case just put some heat exchanger in between space and the freezing cell, so that you can control temperature to the usual -20 Celsius. Also bear in mind that freezing a large carcass just by radiative dissipation might leave the core at "high temperature" for long enough to start to decompose.

Exposure to UV shall be carefully dosed: you want to sterilize the food, not breaking its molecules into unknown radicals. Also, keep in mind that bacteria have survived on the Moon for several years, so don't blindly rely on UV, remember to wash your hands!

Summarizing, it would be possible, but it has do be done in a smart way.

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    $\begingroup$ "bacteria have survived on the Moon for several years" I'm amazed, and I gotta research it now! $\endgroup$ Oct 2, 2018 at 17:04
  • $\begingroup$ @Renan, added reference to that in my answer. Sorry for not doing that earlier. $\endgroup$
    – L.Dutch
    Oct 2, 2018 at 17:46
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    $\begingroup$ Keep in mind that liquids in a vacuum will likely first boil and then freeze, creating a huge area of tiny floating frozen particles, rather than a solid blob. $\endgroup$
    – Shadowzee
    Oct 2, 2018 at 23:11
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In the book The Martian, the main character accidentally freeze-dries his entire potato crop after an atmospheric breach. This is an author who did meticulous research. The potatoes were completely fine, just not as tasty and they could no longer grow and divide.

I'd say freeze drying using the non-atmosphere is an excellent way to prep food for long-term storage.

But as slaughter? No. Aside from the extreme cruelty, you will end up with a hard dry and large dead animal. How will you clean, skin, and gut it? Even a small animal like a bird would be problematic. It would turn soggy when reconstituted. Even fish need to be gutted. For a large animal, gads. But you could do crickets.

The water loss issue L.Dutch brings up may or may not be a problem. Again, using The Martian as a source, water and oxygen were not issues at all, with the machinery the character had available. But this could vary based on the location and the tech, as well as the total needs (in The Martian there was tech for an entire team of people but he was alone).

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  • $\begingroup$ The freezing itself is most probably due not simply to (near-)vacuum exposure, but to decompression. When gas expands, it cools down, and vice-versa, which is the working principle of most freezers. Here, the atmosphere is suddenly vented and decompresses, which would violently drop air temperature until it is mixed with the (tenuous and itself very cold) Martian atmosphere. $\endgroup$
    – Eth
    Oct 3, 2018 at 12:03
  • $\begingroup$ @Eth Add to that the cooling caused by the dehydration itself. As water evaporates, the food cools down by evaporative cooling, which slows down evaporation, so heating is advised. $\endgroup$ Oct 3, 2018 at 17:01

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