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What's the big difference between Dehydrated and Freeze-dried foods? What are the pros and cons to choosing one over the other for backpacking?

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The most significant difference between the two—aside from cost—is the composition of the food due to the different processes of removing moisture.

Dehydration very simply uses heat to remove moisture without cooking the food. This leaves the food withered and hard, and takes a lot longer to rehydrate. Freeze-drying involves freezing the food inside a vacuum chamber, the boiling point of water is well below 0°C in a vacuum, so when you put frozen food in a vacuum the moisture in the food "boils" and is sucked out as a gas. The significant difference is that the freeze dried food retains its structure, and accepts moisture like a sponge. Dehydrated foods do not so readily accept moisture. As a result freeze dried foods will rehydrate or "cook" much faster.

The main differences:

DEHYDRATION

Moisture content: 5 - 10%
Shelf life: 15-20 years (fruits and veggies)
Nutritional value: Dehydration process breaks down vitamins and minerals; retains less nutritional content.
Appearance and composition: Withered and hard
Cooking: 15min - 4hrs; takes a long time to re-hydrate; bland flavour, requires seasoning.
Cost: Dehydrating food is easy and cheap; dehydrators are relatively inexpensive and can be easily homemade using a box and space heater, or even the sun.

  • Pros: Cheaper, simpler process; easy and inexpensive to dehydrate home-made foods.
  • Cons: Longer preparation times; retains less nutritional content; heavier to carry. Shorter shelf life than freeze-dried.

FREEZE DRYING

Moisture content: 1 - 2% (significantly less weight)
Shelf life: 25-30 years (fruits and veggies)
Nutritional value: Vast majority of the vitamins and minerals found in the original food is retained.
Appearance and composition: Moisture is removed from the food without destroying it's structure; becomes soft when wet.
Cooking: 5min - 10min; better flavor.
Cost: Freeze-drying food is not as cheap as dehydrating it; dryers are high tech and cost thousands of dollars, and use more power than dehydrators.

  • Pros: Lighter to carry; tastier; ready to eat in as little as 5-10 minutes preparation time; more nutritious. Longer shelf life
  • Cons: More expensive; home Freeze-dryers are a big investment.

Dehydrated vs. Freeze-Dried Food

The main deciding factor between the two for most people is the often comes down to cost. Buying freeze-dried food is more expensive. You can get home freeze-dryers and freeze-dry your own foods, but the dryers are high-tech and expensive. If you're cost-driven, then carrying dehydrated food may be the way to go.

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    As an aside, freeze dried ice cream is a fun treat. It's not cold nor is it really ice cream any more. More like a dried light nugant, but it's a really good treat.
    – Escoce
    Commented Apr 8, 2016 at 15:05
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    Nice answer. I'd maybe change the then rapidly heating it to above boiling point - while technically true, its important to note that the boiling point at this moment is below 0°C (when most people think about the boiling point of water its likely they mean at 1 ATM pressure, i.e. 100°C).
    – fgysin
    Commented Apr 13, 2016 at 8:02
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if i recall right i think dehydrated food you eat as is and freeze dried food you need hot water to make it edible that would be like cup of soup or cup of noodles and is high in sodium but it will help keep you hydrated but if your backpacking and can't have a open flame on the trail then dehydrated food like fruits will will give you some energy until you get to where you can have a hot meal and both these foods are lightweight for hiking and camping and you would have water with you anyways

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