Camping food : All about Dehydrated, Freeze-dried, … foods

Hiking or trekking is a theme that has been widely covered by adventure magazines, sites and blogs.


Dehydration and freeze-drying are two “drying” processes that conserve food and reduce weight and volume to facilitate storage and transportation.


Dehydrated food is drying by heat. Whether it is industrially treated in hot air dryers, or “homemade” by oven drying, or in domestic dryers, the dehydrated food can lose up to 94% of the water it contains.

This process has the advantage of being relatively inexpensive and thus allows to obtain cheap dishes and available in any shop around the corner.

The major drawbacks of this process are the loss of vitamins sensitive to heat (B1) or oxidation (A and C) and the nutrients it causes (depending on the food, the losses are of the order of 10% to 50% of nutrients for example), as well as the effects produced on certain proteins which make them less assimilable.

Finally, dehydration causes an undeniable loss of organoleptic qualities (taste and flavor) dishes and a “slump” of cells, it is this last point that makes the consistency of a dehydrated dish is not something like the original food.


Freeze-drying is a much longer drying process and technique, resulting in a higher cost. To freeze-dry a food it will be necessary to freeze it, put it under vacuum, and evaporate the so-called “free” ice without melting it (this is called sublimation).

It will then be necessary to extract the last water molecules contained in the food via a high evacuation and a gradual rise in the temperature of the product until it returns to positive values ​​(this is the desorption).

This process can take up to a week! The freeze-dried food will have lost 94% to 97% of its water.

The chemical reactions being maintained at a very low level, a product is obtained whose organoleptic qualities are very well preserved, as are the nutritional and biological qualities, especially protein foods that vary only very little.

Finally, vitamins C and Beta carotene (among the most fragile) support freeze-drying (lyophilization) very well (it is estimated that 10% of losses are maximum).

Freeze-drying produces quality products that rehydrate well, and it is the preservation method that best preserves the qualities of food.

In the traditional trade, it remains reserved for soluble coffee, certain soups, or for aromatics.

Freeze-dried food bags are used by all those who need food self-sufficiency (mountaineers, hikers, journalists, sailors, rowers, astronauts, relief and humanitarian actors, etc.).


Canned foods are simply sterilized products. This process was discovered at the end of the 18th century by a French chef named Nicolas Appert! Sterilizing a food helps to eliminate microorganisms that could reproduce during the storage period.

The process consists of preparing the food, precooking/cooking and sealing it, traditionally in cans or glass jars.

Most often sterilization is done once the product is packaged. It consists of an autoclave heat treatment and a temperature rise of up to 100°C (not to be confused with pasteurization at around 85°C).

This mode of food processing leads to losses of vitamins (B and C in particular) of 30 to 50% or more for certain ingredients, but can keep food between 1 and 2 years depending on their packaging.


Self-heating are, as their name suggests, dishes that contain an internal heating system, they provide a warm canned food without any other equipment to be autonomous.

Obviously heavier than freeze-dried or dehydrated food, they will however be particularly appreciated at very high altitude, where oxygen is scarce and where boiling water becomes difficult, sometimes impossible.

They are also very practical in many other situations: hiking, traveling to be independent or to ensure, in winter in particular, to have a hot meal in his vehicle if you find yourself stuck in a storm of snow for example.

They are also used by emergency services as well as the army.



The regulations on labeling are the same as for all commonly used food products.

The sales denomination (the name of the product / recipe) must be as precise as possible and should normally mention the specific treatment of the product.

The ingredients (including additives) must all be mentioned on the label in descending order from the largest quantity.

Here, as for everyday foods, there are very big differences depending on the recipes.

Some manufacturers have opted for the use of quality ingredients and the limitation or even the total absence of additives.

Others continue to manufacture according to the habits of industrial production, that is to say by opting for a low manufacturing cost, and therefore do not necessarily select the ingredients for their quality.

However, it should be noted that this issue of the quality of our food being a strong concern today, manufacturers are making more and more efforts on the composition of dishes, so hydrogenated fats for example are less and less present in the ingredients.

As regards additives, when the manufacturer uses them, those used are the same as in everyday food products.

Some of these additives (authorized) are controversial when their possible harmfulness to health … but are part of the composition of some recipes … everyone make his choices based on his beliefs.

Finally, note that some foods contain dehydrated ingredients in greater or lesser quantities. We can assume that this can be for certain recipes, modulate their nutritional interest in terms of vitamin intake for example.

As for the food of everyday life, looking at the details of the ingredients of each recipe allows everyone to make their choices according to their own criteria but also according to their budget, because it is obvious that the ingredients of the dish determine largely the price of the latter.

It should be noted that organic and vegetarian freeze-dried meals are now available, as the range of gluten-free products will soon be expanded, and halal recipes will soon be available (they already exist in canned foods).

The calorie intake and carbohydrate-protein-fat is also mentioned, which provides insight into the balance of the diet.

The allergen must be clearly indicated on the labels (regulations considered major allergens peanuts, milk, eggs, soy, fish, crustaceans, shellfish, nuts and sesame seeds, cereals containing gluten, sulphates from 10 mg / kg, mustard, celery and lupine and their derivatives). Although regulations are extremely restrictive for manufacturers to adapt their production chains and procedures, more and more gluten-free and / or lactose-free products are found in freeze-dried recipes.

The net weight of the dish must also appear on the label. We have on the market of main dishes whose net weight varies from 80g to 190g for single portions! As the mode of preparation must also be mentioned, the amount of water to add indicated can calculate the weight of the dish after rehydration. According to the brands and recipes this rehydrated weight varies enormously: 300g to 690g! The impact on calorie intake is not necessarily correlated, but it is on the feeling of fullness that the final weight of the dish will play.

The “good eaters” will prefer more hearty dishes, and the “little eaters” will have any interest in choosing less hearty dishes to avoid not being able to finish their portion (and consequently not to be able to count on the completeness the caloric intake of the chosen dish).

The expiration date or the Best Before End must also appear clearly on the packaging. Freeze-dried organisms designed for activities requiring food self-sufficiency are kept for 2-7 years (but there are some that are kept for 10-25 years thanks to nitrogen packaging, they are mainly intended for humanitarian aid and survival stocks).
To ensure product traceability, the manufacturing lot and the manufacturer’s contact information must also appear on the packaging.

Finally, the total amounts of vitamins and minerals when added to food, the amounts of protein, carbohydrates, sugars, saturated fatty acids, dietary fiber and sodium, as well as the energy value, should be mentioned on the bags.

The total amounts of vitamins, minerals and micro-nutrients naturally contained in the food are not an obligation, it is still found on very few products.

It is therefore difficult to quantify how to prepare one’s self-sufficiency diet, and that is a shame because it may push too many people to use dietary supplements.

We forget that a balanced diet normally brings all the necessary elements to the body.

Again in doubt, one should not hesitate to consult a nutritionist on this point, because if they are sometimes mistaken, some intensive practices and certain pathologies make these supplements essential to not find themselves in a situation of deficiency.


Caloric expenditure varies greatly depending on the age, weight, height, sex, eating habits and lifestyle of the practitioner, his degree of training, but also the duration and difficulty of the course, weather conditions, altitude or the weight of his backpack for example.

Finally, the “involvement” of the practitioner in the activity also influences his expenses.

The same person will have different expenses for the same course, depending on the stress felt and that will obviously be different in the context of a training, a competition depending on the level, a personal challenge (adrenaline can increase energy costs and go up to double them!)

All these parameters do not simplify the evaluation of each one’s personal expenses. It is therefore possible to give a general and approximate idea of ​​the energetic expenses of trekking and itinerant walkers, but for those who practice this activity on a regular or even intensive basis, the consultation of a nutritionist doctor makes it possible to ensure that you do not put your body in danger.

To know its exact energetic expenses, there are different formulas of computation, we will not return here in the arithmetic … but will retain that one obtains a result corresponding approximately to the needs of our basic metabolism by multiplying its weight by 25 for a woman and by 30 for a man. Then add the expenses related to the activity.

Thus it is estimated that walking on relatively flat terrain and practicable in the context of hiking or trekking entails an energy expenditure of 150 to 500 kcal/hour depending on the subjects and the weight of the backpack.

Here again different parameters come to weight these energy expenses: a 10% coast can double the energy expenses, and a descent of 20% will decrease by 25%, the weight of the backpack can still double or even triple them. Side temperature, between 20 and 25 ° C, it is the “thermal neutrality” and the body does not “consume” energy to fight against hot or cold. The further away from this range, the greater the energy consumed by the body will be.

In conclusion, the range of estimate of the energy expenses of the hiker is very broad, but it seems to us that one can say that it is necessary to count about 2500-3500kcal / day in moderate hike and 3500-5000kcal / day in hike supported. When hiking or trekking exceeds 10 days of intensive effort or more than 8 hours of walking a day, needs can climb up to 5000-6000kcal / day. 

Finally, in the polar zone, it is not uncommon for needs to reach 7000-8000kcal / day.


The typical hiking diet consists of a breakfast, which should cover about 20-25% of the daily needs. Usually, a snack will be taken in the middle of the morning (5-10%). A full meal at noon (25-30%) followed by a mid-afternoon snack (5-10%). And a full meal and recuperator at night (25-30%). In the evening, the intake of slow carbohydrates (pasta, semolina, potatoes, etc.) and the foods involved in rehydration (such as soups that also provide mineral salts) will be encouraged.

As a general rule, the recommended distribution of inputs is as follows:

  • Carbohydrates: 55-60% (of which 1/5th of fast carbohydrates at most)
  • Fat: 30%
  • Protein: 15%

For endurance sports such as mountain trekking, it may be necessary to further increase the percentage of carbohydrates in the intakes.

It will also think to hydrate enough, and as often as possible (every 15 minutes is a good pace). Do not wait for the feeling of thirst to drink to avoid under-hydration. The “water bags” are very practical.

The contributions in fresh fruits and vegetables are to be preferred … as much as possible! The weight and conservation constraints do not always make it possible to supplement one’s diet with fresh products, but if there are refueling possibilities on the course, as much to take advantage of it.

Note: pasta or quick-cooking rice are very practical for hiking, but it seems that the pre-cooking of these foods would lead to the modification of their nutritional characteristics. They would actually be closer to fast sugars than slow sugars.

Finally, we find on the internet many sites offering “calculators” to assess its caloric needs according to more or fewer criteria.



Dehydrated food are most often in little bag or containers in the format of a bowl.

The freeze-dried products are packaged in bags that are airtight and light-proof. According to the manufacturers, they have different shapes, can be equipped with a “ziploc” closure, a water level line to add for rehydration or not.
In general, canned dishes suitable for hiking/trek … are packaged in a bag (plastic or plastic and aluminum) also airtight and light, offering a gain in volume, weight and obvious waste if they are compare to cans.

Finally, today we find self-heating meals in 2 forms. Packaged as cans with a magnesium heating system built into the box. They are practical for sure, but their volume and starting weight and the volume and final weight of the waste are rather unacceptable, unless you leave for one or two days.

There is a self-heating new generation meals, that are composed of a meal canned, a simple bag of heating which contains a small membrane composed of lime and aluminum, and a little bag of water of 45ml (for an additional gain of weight one can do without to have little bag and to take any water, even sea water). The whole is grouped in a zipped waterproof plastic bag.

The big advantage of these is the gain in weight and volume initially and in terms of waste. A self-heating meal of this type weighs 410g initially including 300g of food. Once the meal is consumed, there is about 110g of waste for a volume of just a few cubic centimeters. The self-heating canned they weigh about 600g at the beginning of which 250 to 300g of food, once consumed there remains about 300g of waste and practically the same volume as the one of departure.


We can identify three important things to remember for the preparation of dehydrated and freeze-dried food. First of all they require precise water supplies, mentioned on the bag. As all bags do not have a filling line, make sure you have a container to measure the amount of water that is added. Then it is imperative to really stir them. Finally, for cold walkers, this time is to look closely because the temperature of the meal at the time of eating will obviously not be the same if the rehydration take 5 minutes or 30 minutes.

Dehydrated foods should be rehydrated with boiling water. According to the presentation format, the dish is rehydrated in its container or not by pouring water on it. The rehydration time is usually longer than for the freeze-dried, and it is sometimes necessary to boil all the preparation a few minutes.

The freeze-dried food are designed to be rehydrated with hot or cold water (for some dishes/desserts). The bags are designed to be able to eat directly in it, so the water is poured inside. According to recipes and manufacturers, the rehydration time is around 8-10 min most often (but there are freeze-dried foods that rehydrate in 5 minutes and others in 20 minutes) . Once the rehydration time is up, it’s ready, you can eat your meal!

Note that in extreme conditions, it is possible to rehydrate a freeze-dried food with cold water. Some manufacturers mention this possibility on bags and give the necessary rehydration time (usually it is double or triple the usual rehydration time of the recipe). Having no feedback from rehydration of cold products in polar areas, we can not say if this can possibly work under these conditions. However, if you were to find yourself in this situation, we advise you to favor the consumption of food based on potatoes or vegetables, or even pasta. Because the rice-based dishes they rehydrate much less well in cold water, even by waiting a very long time.

The canned goods do not require any rehydration, and they must be reheated immersing the meal bag in boiling water for about ten minutes or empty the bag content directly in a cooking pot. as you would do for a can at home). They can also be eaten cold since they are already cooked.

The self-heating heating system in canned foods is triggered by pressing strongly on a defined area. Then you have to wait 10-12 minutes, then you can open the can and consume your meal. For self-heating bags, you must tear the top of the heating bag (containing the membrane), slip the unopened meal bag, pour 45ml of water.

Then fold down the top of the heating bag and wait 10-12 minutes. It is normal to see water vapor escape from the bag at this time because this system reaches 80°. Once the heating time has elapsed, we take out the meal packet, we open it and we can consume the hot meal.

If you are in the cold, you can take advantage of the heat of the heating system that will last another hour, putting it in a jacket pocket for example (be careful not to burn yourself, because it is obviously not studied for this at the start and that the membrane remains very hot even after 30 minutes).

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