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I'd like to experiment with freeze drying food but the only equipment I own, is a vacuum pump+chamber and an old freezer I wouldn't mind drilling to run a vacuum pipe inside.

However an important point is to flash freeze the food, otherwise I would lose much benefit of the freeze drying process. So, I wondered if I could have a good enough result by immerging the food (in a plastic bag) in water+salt/antifreeze solution at -18°C or lower.

The reason of choosing this temperature, is that I can produce it (or even lower e.g. -21°C, -24°C) with a good freezer - no need for special equipment. And the reason for choosing water, is it's massive thermal inertia. So the question is : What kind of solution would give me the best result (As much as possible, with the lowest toxicity risk with the lowest toxicity, for the antifreeze product). I know that I can get something around -21°C with normal kitchen salt, but are there better solutions without loosing too much of my water's thermal inertia ?

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Freeze drying food requires rapid and consistent cooling of the food in order to flash freeze it. The goal is to freeze the food quickly so that the water inside the food turns into ice crystals without forming large ice crystals that would cause damage to the structure of the food.

The solution you suggest of immersing the food in water and salt/antifreeze at -18°C or lower should be effective in flash freezing the food. The use of salt will lower the freezing point of water, allowing it to reach lower temperatures, and the antifreeze can also be used to reach lower temperatures if needed. However, it is important to note that some antifreeze products contain toxic chemicals and should not be used for food preparation.

It would be best to use a food-grade antifreeze, such as propylene glycol, which has low toxicity and is commonly used in food processing. Another option is to use a mixture of water and ethanol, as ethanol is commonly used in food as a preservative and has a lower freezing point than water.

In conclusion, you can use a solution of water and salt or water and food-grade antifreeze to flash freeze your food, but make sure to use a food-grade antifreeze product to minimize the risk of toxicity.

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  • $\begingroup$ Yep, Using a 40% or a bit more Alcohol might be the best & safest solution. Its thermal inertia is a bit lower than pure water, but it's easy to compensate by just using a bit more, and since it's density will be slightly lower, it might also make easier to keep the food under the surface, which might turn more difficult with salted water. Thank you for the suggestion. thespruceeats.com/will-liquor-freeze-760302 engineeringtoolbox.com/ethanol-water-d_989.html $\endgroup$
    – Camion
    Commented Feb 8, 2023 at 18:26
  • $\begingroup$ In fact, I could even use pure ethanol, to avoid having to dilute it, so that I could keep it for any other needs... $\endgroup$
    – Camion
    Commented Feb 8, 2023 at 21:16

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