22 mai 2025

Dehydrating plant-based meals for hiking

The short version

A home-dried plant-based meal weighs three to four times less than the same cooked dish, but whether the result is safe depends on three things most tutorials skip: drying temperature, pretreatment, and how you check that drying is actually finished.

The American extension services publish the most detailed home-drying protocols available, and they agree on specific numbers. Penn State Extension sets the dehydrator at 145°F (62°C) while surface moisture is still present, then drops it to 135 to 140°F (57 to 60°C) after an hour to finish. For oven drying the same source gives 140 to 150°F (60 to 65°C) with the door propped open 2 to 3 inches, and NDSU Extension caps the useful range at 140 to 145°F. Dry too hot and you get case hardening: the surface forms a crust and traps moisture in the centre of the slice. Dry too cool and the food spends far too long in the range where bacteria multiply.

The rest comes down to four habits. Blanch vegetables before drying. Soak light-coloured fruit in an acidic solution. Condition dried fruit for four to seven days before it goes into long-term storage. And on the trail, rehydrate with water brought to a rolling boil, never with cold water left to soak for hours in a pack.

What drying actually does to food

Drying removes free water until micro-organisms can no longer grow. The mechanism is physical: heat evaporates the moisture and moving air carries it away. Both matter, as Penn State Extension points out. Plenty of heat with no airflow gives you food that is cooked on the outside and damp in the middle.

The composition figures from USDA FoodData Central show what you gain. A raw peeled apple holds 86.7 g of water per 100 g and provides 48 kcal. Dried apple drops to 31.8 g of water and concentrates 243 kcal per 100 g. Dry lentils contain 8.26 g of water, 24.6 g of protein and 352 kcal per 100 g; boiled, they shift to 69.6 g of water, 9.02 g of protein and 116 kcal. Raw white rice sits at 11.6 g of water against 68.4 g once cooked.

That arithmetic has a consequence hikers often miss. Drying a cooked dish does not make it lighter than the dry ingredients you started with. A bag of raw rice and dry lentils is already at minimum weight. What precooking and drying buys you is rehydration time on the stove and fuel saved, not grams in the pack.

One more point that gets glossed over: drying improves nothing. The extension services say so plainly, preservation never upgrades food quality. A bland apricot dried is a bland apricot, dry. Start with ripe, sound produce and discard anything showing bruising, mould or decay.

On household energy, drying is reasonably frugal. Penn State Extension notes that the energy input is lower than freezing or canning, and that storage space is smaller too. That said, a dehydrator running for twelve hours is not free, and an oven held open for ten hours certainly is not. Batch your loads.

Choosing a method: dehydrator, oven, sun

Electric dehydrator

This is the reliable option, because it pairs a thermostat with forced airflow. Penn State Extension describes a two-stage setting: preheat, load at 145°F (62°C) while the pieces still have surface moisture, then drop to 135 to 140°F (57 to 60°C) after one hour so the slices finish without crusting.

The main weakness of these machines is uneven drying between trays. On many vertical-flow models the bottom tray sits closest to the element and dries fastest. Rotate the trays halfway through instead of trusting a printed time.

Oven

An oven works if you first check that it goes low enough. NDSU gives a straightforward test: set it to the lowest setting, put an oven thermometer on the rack where the food will sit, leave the door open 2 to 6 inches, place a fan near the opening to circulate air, then read the temperature. If it holds 140 to 145°F (60 to 63°C), you can dry in it. If it will not go below 175 or 195°F, it will cook your food rather than dry it.

Space the racks about 2 inches apart with at least 3 inches of clearance top and bottom. NDSU adds a sensible warning that food blogs tend to leave out: an oven propped open for hours is not a safe setup with young children or pets around.

Expect roughly double the time of a dehydrator. A fan oven does better, since it already combines low heat with air movement.

Air and sun drying

Sun drying works in hot, dry climates. Penn State Extension calls the method impractical where humidity is high, and a Swiss summer regularly qualifies. Room-temperature drying only works when heat, humidity and airflow all cooperate, which is rarely the case in an air-conditioned or simply cool home.

Keep the sun for herbs and thinly sliced fruit during a settled spell of weather, and never for cooked dishes. If the idea appeals anyway, we cover the build and the limits in our piece on making a homemade solar dehydrator.

Pretreatment, the step people wrongly skip

Blanching vegetables

Blanching is not cosmetic. NDSU lists four effects: it destroys the enzymes that cause colour and flavour problems in storage, it kills part of the microbial load, it softens the cell structure so moisture escapes faster, and it makes the pieces rehydrate faster later on. That last point matters enormously when you are cooking at 2,000 metres with a counted gas canister.

The protocol is short. Bring a large pot to a rolling boil with a quarter teaspoon of citric acid per quart of water, which works as both an anti-darkening and an anti-microbial agent. Lower the vegetables in a basket or colander, no more than a quart at a time, start timing when the water returns to the boil, then cool in cold water for the same length of time as the blanch. Drain well. Water blanching gives more even heat penetration than steam or microwave blanching.

Onions, garlic, peppers and herbs need no blanching at all.

Treating light-coloured fruit

For apples, pears, peaches and apricots, a ten-minute acid soak before drying limits oxidation and preserves colour and texture. The reason that really justifies the step lies elsewhere: Penn State Extension states that research has shown pretreating with an acidic solution enhances the destruction of potentially harmful bacteria during drying.

Three equivalent solutions are documented. NDSU offers 2½ tablespoons of pure ascorbic acid crystals per quart of cold water, or 1 teaspoon of citric acid per quart, or equal parts lemon juice and cold water. In each case, soak for ten minutes, drain, then dry.

Tough-skinned fruit such as grapes, plums, cherries and blueberries needs its skin cracked: 30 to 60 seconds in briskly boiling water, then a plunge into very cold water and a blot dry. Without that, the waterproof skin blocks evaporation.

We leave sulphiting out. Penn State Extension advises against it for people with asthma or respiratory conditions and for anyone on a restricted-sodium diet, and requires sulphited food to be dried outdoors. The trade-off makes no sense for a camping pot.

Blanching and drying times, vegetable by vegetable

The times below come from the NDSU Extension table, adapted from Colorado State University using University of Georgia blanching and drying times. They apply to a dehydrator; in an oven, allow up to double.

Vegetable	Preparation	Blanch	Dry	Dryness test
Carrots	Thin slices or strips	3½ min	10 to 12 h	Tough to brittle
Peas	Shelled, washed	2 min	8 to 10 h	Hard, wrinkled, green
Green beans	Cut into pieces	2 min	8 to 14 h	Very dry, brittle
Sweetcorn	Blanch on the cob, then cut	1½ min	6 to 10 h	Crisp, brittle
Potatoes	¼-inch strips	5 to 6 min	8 to 12 h	Brittle
Courgettes	¼-inch slices	1½ min	10 to 12 h	Leathery to brittle
Mushrooms	10-min citric acid dip	None	8 to 10 h	Dry and leathery
Onions	¼-inch slices	None	3 to 9 h	Very brittle
Peppers	¼ to ½-inch strips	None	8 to 12 h	Tough to brittle
Tomatoes	Peeled, ½-inch slices, 10-min acid dip	1 min	10 to 18 h	Crisp
Herbs	Separated into clusters	None	1 to 2 h	Flaky

Mushrooms carry a warning that NDSU prints in capitals: neither drying nor cooking destroys the toxins in poisonous varieties, and only an expert can tell edible species apart. Dry only shop-bought mushrooms or ones cleared by an official inspector.

For fruit, NDSU gives 6 to 12 hours for apples sliced 1/8 to 1/4 inch, 6 to 10 hours for bananas at 1/8 inch, 24 to 36 hours for apricot halves, 12 to 24 hours for figs, and 6 to 10 hours for pear slices against 24 to 36 hours for pear halves. Thickness drives everything.

Drying a complete cooked meal without getting it wrong

This is the use hikers care about most, and it is also the one with the fewest validated public protocols. The extension services document fruit, vegetable and meat drying in detail, and cooked stews far less. So you apply the principles rather than following a fixed recipe, and you keep a safety margin.

The approach that respects the known parameters:

Cook normally, seasoning more assertively than usual, because drying blunts volatile aromas.
Cut the fat down hard. Fats do not dry, they go rancid. A curry built on coconut oil, or a sauce finished with olive oil at 100 g of fat per 100 g according to USDA figures, will store badly. Add the fat on the trail instead.
Cool it fast. The UK Food Standards Agency asks you to cool cooked food and get it into the fridge within one to two hours, dividing it into smaller portions to speed things up. Do not let a stockpot sit lukewarm overnight before it reaches the dehydrator.
Spread very thin, 5 mm at most, on a non-stick sheet or baking paper. A thick layer dries on top and stays wet underneath.
Dry at 135 to 145°F (57 to 63°C), as for vegetables, and break the sheet up halfway through to expose the hidden faces.
Finish properly. The result should be brittle or crumbly, never pliable, never tacky.

The hazard here has a name: Bacillus cereus. The FDA Bad Bug Book describes this spore-forming bacterium as classically associated with rice and other starchy foods. Its emetic toxin, cereulide, remains stable after heating at 121°C for 30 minutes and survives refrigeration. In plain terms, once the toxin has formed, neither cooking nor rehydrating with boiling water removes it. The spores themselves survive drying. So the whole point is never to let a starchy dish sit at lukewarm temperature, either before drying or after rehydration.

The same reasoning drives our discussion of cooking and keep-warm functions in how to cook a complete meal in a rice cooker.

Checking that it is genuinely dry

Incomplete drying is the leading cause of failure, and it announces itself three weeks later as mould at the bottom of a food bag, halfway through a trek.

Always let a sample cool before testing, because a warm piece feels softer than it is. Vegetables should be tough, brittle or frankly crisp. Fruit should not go hard: NDSU describes the target as leathery and pliable. The test is to squeeze a handful of cooled pieces; they should spring apart when released, without sticking. Then cut two or three pieces in half: no visible moist area, no beads of moisture when pressed between your fingers.

Conditioning fruit, the step nobody knows about

Pieces on the same tray never dry perfectly evenly. Conditioning equalises the residual moisture between them and lowers the risk of mould.

NDSU’s protocol: place the cooled fruit loosely in glass or plastic containers. Cover lightly. Keep in a dry, well-ventilated place for four to seven days, stirring or shaking the container daily. If condensation appears on the walls, return everything to the dryer and then repeat the conditioning.

Dried vegetables, brittle by nature, do not need this step.

Penn State Extension adds a rarely mentioned treatment for unpeeled or uncovered fruit, aimed at destroying any insect eggs: either 30 minutes in the oven at 160°F (71°C), or 48 hours in the freezer at 0°F (minus 18°C) or below.

Packing and storing

Pack in small amounts, in dry glass jars, preferably dark, or in moisture- and vapour-proof containers and bags. NDSU notes that metal tins are fine if the food goes into a freezer bag first. Clear glass has a practical advantage: you see condensation immediately if the drying fell short.

Store cool, dry and dark, or in the fridge or freezer. Light degrades vitamins and colour. Under those conditions NDSU gives both dried fruit and dried vegetables a shelf life of six to twelve months. Discard without hesitation anything with an off odour or flavour, or any sign of mould.

Label every container with contents, date and, for cooked meals, how much water to add. On the trail nobody remembers whether the grey pouch takes 200 or 350 ml. Split into single portions: every time you open a large jar you let ambient humidity back into the whole stock.

These principles reach beyond hiking; we extend them to the whole pantry in proper storage of fruit, vegetables and legumes, and drying sits alongside the other techniques in anti-waste practices: freeze, ferment, dehydrate.

Rehydrating in the field

The volume rule of thumb comes from NDSU: one cup of dried vegetables becomes two cups when reconstituted. Remember the ratio, it beats guessing by eye.

The same source separates two cases. For leafy greens, kale or spinach, cover with hot water and simmer to the tenderness you want. For root and seed vegetables, beans, corn, carrots, cover with cold water and soak for about an hour, then simmer.

For a dried cooked meal, pour boiling water over the powder or shards, stir straight away to avoid lumps, cover, then simmer five to fifteen minutes depending on density, adjusting the water. A lid and an insulating cosy cut gas use noticeably.

Two safety rules frame all of this.

Water quality first. The WHO points out that microbial contamination from faeces is the greatest risk to drinking-water safety, and that contaminated water transmits cholera, dysentery, typhoid and hepatitis A among others. A stream that looks clear guarantees nothing: a pasture upstream is enough. The WHO technical brief on boiling is explicit that heating water to a rolling boil is sufficient to inactivate pathogenic bacteria, viruses and protozoa. A membrane filter or a suitable chemical treatment are alternatives, but a genuine boil remains the reference, and you need it for the meal anyway.

Cold rehydration second. It suits dried fruit you snack on and acidic preparations. Avoid it for starchy dishes based on rice, pasta or potato left to soak for hours in a lukewarm bottle strapped to a pack, precisely because that scenario matches the growth conditions for Bacillus cereus described by the FDA. If you want a head start, soak for thirty minutes at most, then bring to the boil.

Finally, do not reheat yesterday’s leftovers the next morning. At home the Food Standards Agency already limits leftovers to 48 hours in a fridge held at 0 to 5°C. On a trail with no refrigeration, the only sensible approach is to cook the portion you are about to eat.

A dry trail menu inevitably leans on carbohydrates and dense fats. That does not excuse you from thinking about protein, especially over several days.

The Swiss reference points from the FSVO give a usable frame: one daily portion of a protein-rich food, meaning 60 g of raw legumes or 120 g of tofu, three portions of starchy foods where one portion is 45 to 75 g of flakes, pasta or rice by dry weight, a small handful of 15 to 30 g of nuts or seeds, and 1 to 2 litres of unsweetened drinks a day. Those figures describe an ordinary day; sustained effort raises energy and fluid needs without changing the logic of the split.

Dry lentils remain the most efficient single ingredient here, at 24.6 g of protein, 10.7 g of fibre and 6.51 mg of iron per 100 g according to USDA data, for minimal carried weight. Almonds bring 21.2 g of protein and 49.9 g of fat per 100 g, an energy density that is hard to beat. The NHS emphasises variety across protein sources rather than a compulsory pairing at every meal, which we develop in our complete guide to plant proteins.

A word on supplements, without promises or dosages. A few days of hiking does not create a deficiency. Vitamin B12 is a question for a vegan diet as a whole rather than for a trek in particular, and it belongs to individual follow-up; we set out what is known in our article on vitamin B12. For hydration and electrolytes during effort, see natural hydration and electrolytes for vegetarian athletes instead.

Three preparations that work

Rice, lentil and vegetable base

Cook rice and red lentils separately, mix with blanched diced carrot and pepper, season generously with curry, cumin and paprika, then spread 5 mm thick and dry at 60°C until brittle. In the field, use two volumes of boiling water to one of mix, let it swell covered, then add oil and nuts as you serve.

Soup base

Cook the vegetables in stock, blend, spread very thin, dry, then break into shards and grind to a coarse powder in a mortar or food processor. The powder rehydrates in minutes with boiling water. It is the fastest preparation in the repertoire and the most forgiving of measuring errors.

Fruit leathers

Penn State Extension gives precise parameters: spread the purée about ¼ inch (6 mm) thick on plastic dehydrator sheets or a tray lined with smoothed cling film, never waxed paper or ordinary aluminium foil, which the leather sticks to. Two cups of purée cover a 13 by 15 inch sheet. Drying at 140°F (60°C) takes anywhere from six hours to several days depending on the fruit and thickness. It is ready when pressing the centre leaves no indentation and no wet spot. Peel while warm, roll, cool, then wrap. These leathers keep up to one month at room temperature and up to a year frozen. Add 2 teaspoons of lemon juice or 1/8 teaspoon of ascorbic acid per 2 cups of light-coloured fruit to prevent darkening.

For snacks that need no drying at all, see hiking: long-lasting raw energy bars, and for planning a multi-day menu, preparing hiking meals.

Ten mistakes that cost you a batch

Setting the dehydrator to 105 or 115°F to “preserve nutrients”. No official protocol recommends those temperatures for vegetables or cooked dishes, and the time spent in the bacterial growth range stretches out accordingly.
Cranking it to 175°F to speed things up. That is the recipe for case hardening: an outer crust, trapped moisture, mould in storage.
Skipping the blanch on vegetables. Colour drifts, the flavour turns hay-like after three months, and rehydration drags on forever.
Drying a fatty dish. Fats do not dry, they go rancid. Add the oil on site.
Testing dryness on a piece that is still warm. It will feel softer than it really is.
Skipping the conditioning of fruit. Residual moisture concentrates in the thickest pieces and starts the mould.
Storing in one big jar. Every opening lets humidity back into the entire stock.
Forgetting to label. Three pouches of brown powder look identical at a bivouac.
Soaking a rice-based dish in a bottle all day. See Bacillus cereus above.
Rehydrating with untreated water. It may not boil long enough if you eat after five minutes of resting under a lid.

Adapting to the situation

Day walk. Drying is pointless: take bread, cheese, fresh fruit. Dehydration starts paying off from two nights out.

Bivouac without a stove. Stick to food you can eat dry: fruit leathers, crisp vegetables, nuts, bars. Do not count on cold-rehydrating a cooked dish.

Hot weather. The inside of a pack easily reaches 35 or 40°C in full sun. That is one more reason to avoid fatty preparations, which go rancid faster, and to carry no already-rehydrated food.

Altitude. Water boils at a lower temperature as you climb, which lengthens cooking and rehydration times. This is where blanching your vegetables beforehand really pays, since it cuts the time needed on the stove.

Shared kitchen. If other members of the household are drying animal products at the same time, keep the trays separate and clean thoroughly between loads, in line with the basic hygiene principles the WHO sets out.

Common questions

Can you dehydrate cooked legumes? Yes, and it is one of the most useful preparations, since it saves soaking and cooking on the trail. Cook them fully, drain, rinse, spread in a single layer and dry until hard. The cooking method itself is covered in successful legume batch cooking.

Do I need a vacuum sealer? It helps, but it is not essential. A dry glass jar, filled and sealed tight, stored in the dark, holds the six to twelve months NDSU quotes. Vacuum packing becomes worthwhile for large stocks or longer horizons.

How do I know whether last year’s pouch is still good? Look, smell, taste a piece. A rancid smell, a cardboard taste, a clearly shifted colour or any spot of mould means the whole batch goes. Doubt is not negotiable here.

Does drying destroy vitamins? It degrades some of them, as any preservation method involving heat and oxygen does. Acid pretreatment and dark storage limit the losses according to Penn State Extension. No general number can be given, because the loss depends on the fruit, the cut, the temperature and the duration.

Can I dry herbs from the garden? Yes, and it is the simplest case: no blanching, one to two hours of drying, a flaky result. The other options for herbs are compared in preserving herbs.

What about tomatoes? They readily reabsorb moisture from the air, which shifts colour and flavour, as NDSU notes. Dry them far longer than you expect, up to 18 hours, condition them like fruit and store them in the fridge. We go through their other transformations in tomato transformation.