Onions, dried (dehydrated, dried, organic?, raw?)

Dried onions in strips or pieces are also called onion flakes. They are made from sliced (in rings), dehydrated (dried) and chopped Onions ( Allium cepa). Organic quality is worth it.

Use in the kitchen

Dehydration is the scientific term for drying, eg dehydrating, but also for all other drying processes. Dehydrating is a good way to preserve excess food for longer. The taste also changes. After drying, onions no longer taste spicy, but rather sweet. By using dried onions, there are no more tears when preparing food.

Onion flakes go well with vegetable, pan-fried or braised dishes. They can be used to refine salad dressings, sauces, vegan soups or spice mixtures. As a garnish for salads, pasta or dishes with potatoes, they are a fat-free alternative to fried onions.

Is it possible to rehydrate onions? You can soak dried onions to rehydrate them. To do this, cover the dried onions with hot water and wait until the pieces have the desired consistency; fry gently (or not at all).

Commercially purchased onion flakes are not considered raw food (see the Purchasing and Industrial Production chapters below). If you want to consume a raw product, it is best to make the dried flakes yourself. White and red onions as well as vegetable onions are suitable. You can also use winter onions (spring onions, leek onions) for drying, but commercially available onion flakes are made from onion bulbs. Dehydrated spring onions are a separate product (see: Spring onions, only stems and leaves).

Dried onion pieces make an aromatic snack for in-between meals. To make flakes, you can crush dehydrated onion rings in a mortar or chop them up using a blender or an electric coffee grinder. Finely ground onion flakes are known as onion powder (onion granules).

Homemade preparation

Can you make onion flakes yourself? You need onion rings and a dehydrator or oven. All onions in all shapes and colors are suitable for dehydrating. After peeling the onions, cut them into rings that are as thin as possible. The best way to do this is to use a fine vegetable or truffle slicer. Then distribute the cut onion rings evenly on the trays of the dehydrator or on a baking tray covered with baking paper. The onion rings should not be thicker than 1-2 mm. The thinner the thickest slices, the faster the drying process. A normal-sized baking tray holds about 4 onions.

If the drying temperature remains between 40 and 42 °C, the dried onions are still of raw food quality. The dehydrator allows you to set the temperature precisely, so the drying process takes about 6 hours. Dried onions are ready when they are hard, dry and brittle. You can then chop the dry rings as required (see above).

It is more complicated to dry onions in the oven. Many ovens cannot be set below 50 °C. If the oven is preheated, the finely chopped onions can be dried gently for around 5 hours. You need circulating air and a piece of wood or metal to wedge in the door so that the moisture can escape.

If you want browning, you can set it at 140 °C for about 30 minutes and then reduce it to 100 °C for an hour. We advise against this, however, because this causes the unhealthy Maillard reaction. Such non-enzymatic browning reactions may taste very appealing, but they can lead to mutagenic or carcinogenic compounds (e.g. acrylamide). They mainly form at temperatures of 170-190 °C, but they also occur at lower temperatures, just more slowly.

Vegan recipe for onion and tomato bread

Ingredients: 1 cube of fresh baking yeast, 0.5 teaspoon of sugar, 1 teaspoon of salt, 3 tablespoons of rapeseed oil, 400 g wheat flour, 3 tablespoons of dried onions (organic), 70 g of dried tomatoes, 30 g of pine nuts, 2 tablespoons of dried rosemary.

Preparation: Stir yeast and sugar in 200 ml of lukewarm water until smooth. Mix salt, flour and oil together, add the yeast water and knead together. This works great in a food processor, but you can also knead the dough well with your hands on a floured work surface. Knead in more water or flour depending on the consistency. Then cover the dough and let it rest in a floured bowl in a warm place for about 45 minutes and "rise". Spread baking paper on a baking tray. Knead chopped tomatoes, onions and pine nuts into the dough, halve the dough and roll it out lengthwise. Cover the dough in this or a similar form and let it rise again on the tray for about 20 minutes. In the meantime, preheat the oven to 220 °C top and bottom heat. After the rising time, cut the bread with a sharp knife, brush with water and sprinkle with a little rosemary. After 10 minutes of baking, reduce the temperature to 200 °C and bake the vegan breads for about 20-25 minutes.

Vegan recipes with onion flakes can be found under the note: " Recipes that have the most of this ingredient ".

Purchasing - Storage

Onion flakes can sometimes be purchased from supermarket chains such as Coop, Migros, Denner, Volg, Spar, Aldi, Lidl, Rewe, Edeka, Hofer, Billa etc. or in organic supermarkets such as Alnatura and Denn's Biomarkt. Some well-stocked supermarkets sell onion powder and freeze-dried onion pieces in jars or onion flakes in spice mills. However, for dehydrated onions it is better to visit health food stores, organic shops or order online. Dried onions are usually packaged in screw-top jars or vacuum bags. If possible, buy regionally produced organic onion flakes; many products come from America or Asia. This despite the fact that Central Europe offers ideal growing conditions for onions.

You can assume that purchased dried onions are not raw food quality. This is because they are dried conventionally at temperatures of 82-104 °C. Dried onions are to be distinguished from so-called fried onions (which mostly contain oil, salt, sometimes flour; sometimes fried). Onion granules (onion powder) are also available.

The availability of onion flakes (dried onions) varies depending on the size of the store, catchment area, etc. You can find our recorded food prices for the DA-CH countries above under the ingredient image - and by clicking you can see their development at various suppliers.

Storage tips

Dehydrated onions should be stored in a cool, dry place. Airtight packaging is required, otherwise they will absorb moisture from the air. Screw-top jars, freezer containers or plastic bags that can be sealed airtight are best. If properly sealed, dried onions will last for up to 12 months.

Ingredients - Nutritional values - Calories

Compared to raw onions, dry onion flakes contain hardly any water. The carbohydrate content increases many times over due to the removal of water. When heat is added (drying, frying, steaming, cooking), the glycosidic compounds they contain release sugar. This is why dried onions taste much sweeter than fresh ones. The calorie content is 349 kcal/100g.

The vitamins contained in 100 g increase as follows: Vitamin B₆ (pyridoxine) increases from 0.12 mg (in fresh onions) to 1.65 mg/100g in dried onions. This proportion is similar to that of garlic powder. The vitamin C content is also very high at 75 mg/100g for a processed product (gentle drying is an advantage): fresh onions have around 7.4 mg of vitamin C per 100 g. The folic acid in dried onions (166 µg/100g) is comparable to the content in dried shiitake (163 µg/100g). Note that with dried onions you consume much smaller amounts than 100 g.

Other essential nutrients worth mentioning are: potassium, manganese and calcium. ¹

The complete ingredients of dehydrated onions, the coverage of the daily requirement and comparison values with other ingredients can be found in our nutrient tables. In the article Nutrients explained you will get a detailed insight into the topic.

Effects on health

Dried onions are easier for many people to digest, and stomach problems or flatulence rarely occur. Gently dried onions have similar positive properties to fresh onions, but the drying process can lead to the loss of vitamins and bioactive secondary plant substances.

Secondary plant substances

Our article on secondary plant substances provides an overview of the classification of substance groups, their occurrence in food and possible effects on humans. Dried onions contain the following secondary plant substances: ^2.21

• Isoprenoids: Essential oils; Triterpenes: Steroids (Stigmasterol,Beta-Sitosterol, Campesterol), Saponins (Steroid Saponins, Spirostane, Triterpene Saponins)
• Polyphenols: Phenolic acids: hydroxybenzoic acids (benzoic acid, protocatechuic acid, anisic acid, vanillic acid, syringic acid), hydroxycinnamic acids (cinnamic acid, chlorogenic acid, rosmarinic acid, sinapic acid, ferulic acid, caffeic acid); Flavonoids: flavonols (quercetin, quercetin glucoside, quercetin derivative, kaempferol, kaempferol glucoside, isorhamnetin, fisetin, morin, myricetin, laricitrin), flavones (apigenin, apigenin glucoside, luteolin, diosmin, cirsilineol), flavanones (naringenin, naringenin glucoside, Naringin glucoside, eriocitrin, didymine, hesperetin, hesperidin, taxifolin), flavanols (catechin, epicatechin, epigallocatechin, epicatechin gallate), isoflavones (daidzin, glycitin), anthocyanins (cyanidin glucoside, cyanidin, peonidin, isopeonidin, delphinidin, delphinidin derivatives , pelargonidin derivatives); Lignans (Arctigenin, Medioresinol, Conidendrin, Syringaresinol); Phenols (catechols, pyrogallol, lunularin); Stilbenes (resveratrol, polydatin), xanthenes (norathyriol, lunularin)
• Organic sulfur-containing compounds: Sulfoxides: ajoene, S-alk(en)yl-L-cysteine Sulfoxides (isoalliin, propiin, methiin); thiosulfates (alliin, allicin, vinyldithiin); sulfides (diallyl sulfide, diallyl disulfide, diallyl trisulfide); cepaenes; onionanes (1,3-diethanes)
• Other organic compounds: aldehydes; alcohols; alkanes; quinones; coumarins (scopoletin, esculetin, psoralen); benzofurans (mellein); hydroxycarboxylic acids (oxalic acid, citric acid, malic acid); dicarboxylic acids (fumaric acid)

However, it should be noted that the composition of secondary plant substances in dried onions can vary depending on the variety, time of harvest and growing conditions. Therefore, quantities are only of limited use and should only be understood roughly.

The drying process can significantly affect the phytochemical, antioxidant and functional properties of dried onions. Different drying temperatures and times can lead to variations in the content of phytochemicals and antioxidants, color and texture of the dried onions. ²¹

Essential plant oils are generally quite complex in composition and contain volatile components that are more or less altered during preparation. The volatile fractions of essential oils mainly contain monoterpenes as well as aliphatic aldehydes, alcohols and esters. ²¹ Several studies report on the antitumor, antimycotic, anti-coagulant, cytotoxic, cholesterol-lowering and antispasmodic effects of saponins isolated from onions. ²

One study shows that activity against free radicals correlates with the total phenol content of onion plants (this study recorded the highest activity in red onions; yellow onions were also significantly better radical scavengers than garlic). ¹⁹ This antioxidant strategy is crucial for the prevention and treatment of cancer by inhibiting cancer cell proliferation. ⁵

The flavonoids contained in onions improve blood circulation and prevent blood clots and arteriosclerosis by blocking the oxidation of lipoproteins. The essential oil and flavonoids also have antibiotic, bronchial, anti-asthmatic, cardio-vascular, diuretic and anti-cancer properties. ^2,3 When taken internally (raw, cooked, fried, as a syrup, etc.), onions are effective against all types of respiratory diseases. ³

The antioxidant sulfur compounds have an antibacterial effect and lower blood pressure, blood lipids and blood sugar. ² A 2015 publication examined the best-known health studies on onions and garlic. The study describes the following in terms of cancer prevention: Studies indicate possible mechanisms of the anti-cancer activity of various Allium plant extracts and preparations and underline the activities of the sulfur-containing compounds. These compounds show effects at every stage of carcinogenesis and influence many physiological processes that positively modify the risk of cancer. ⁴ The study recommends that future studies focus on interactions with other nutritional factors such as total fat intake, selenium, methionine (amino acid) and vitamin A. Further studies on the effect of onion vegetables on thiol levels (protection against free radicals) are also required. ⁴

Growing organic onions is a laborious process, but organic quality pays off: Organically grown bulbs contain more healthy minerals and trace elements than those from conventional production. ¹⁸ In addition, fungicides are often used in conventional cultivation.

Dangers - Intolerances - Side effects

Although most onions are poisonous or indigestible for humans, kitchen onions are actually good for maintaining our health. However, they can be poisonous for other mammals (eg cats and dogs). The sulphur substances they contain destroy their blood cells. This also applies to dehydrated onions.

Some allergy sufferers develop contact eczema. Low molecular weight sulfur compounds are considered allergens - such as those found in garlic. Onions contain other proteins that can trigger allergies: lipid transfer protein (All c 3), profilin (All c 4, cross-allergen with grass pollen), alliin lyase (cross-allergen with other types of allium). ⁶

Folk medicine - natural healing

Allium plants have an external effect on warts and corns. ⁸ Onions are also a well-known traditional home remedy for respiratory diseases and colds. You can find more information under the ingredient onions, raw.

Ecological footprint - animal welfare

Despite extensive research, we were unable to find any precise figures on the ecological footprint of onion flakes. The figures depend on the individual production processes, starting with onion production, subsequent processing and finally packaging. Regionally grown onions have a low _carbon footprint (0.2 kg CO ₂ eq/kg). ¹² In a study on the environmental impact of onion cultivation, it was found that the equipment required and the corresponding electricity have the largest share of the environmental impact. In addition, small farms have a greater impact on global warming than larger ones. ¹³ Research is currently being carried out into the use of solar energy to dry onions, as this could be an environmentally friendly alternative to conventional methods. ¹⁵

The amount of water required to produce 1 kg of dried onions is 345 litres, which is higher than the value for onions (272 litres). ¹⁴

A study of the water footprint of dried onions in Nigeria showed that water reserves are used for irrigation. This has a particularly negative impact in a country with a prevalent water shortage. Ideally, rainwater is used instead. ¹⁶

For detailed explanations of various sustainability indicators (such as ecological footprint, _CO2 footprint, water footprint), see our article: What does the ecological footprint mean?

Worldwide occurrence - cultivation

The onion is one of the oldest cultivated plants. It has been used as a medicinal plant, spice and vegetable for thousands of years. Since there are no direct wild ancestors of this Allium species, the geographical origin cannot be clearly determined. ⁹ According to pharmacist M. Pahlow, summer onions originate from western Asia and the Romans brought them to Central Europe. In the Balkan countries and the Orient, the onion is a more important vegetable plant than in western countries. ⁷

Organic farmers struggle with pesticide-free onion cultivation, especially with the high weed pressure. Downy mildew can also lead to significant crop failures. For this reason, organic onions are significantly more expensive than conventionally grown ones. ¹⁸

When the first dehydration experiments were carried out towards the end of the 18th century, they were also tested on onions. In the 1920s, an extensive program for drying onions and garlic was started in California. Commercial drying processes became established at the beginning of the Second World War. ¹¹

Cultivation - Harvesting

There is a huge variety of onions and a large number of different colors. There are mainly red onions (which appear more purple), yellow onions (from beige to light brown) and white onions. A distinction is made between summer and winter onions. Summer onions are the actual kitchen onions; they are sown in spring and harvested between August and October. Winter onions are sown in August and harvested in June/July. They are a little milder ⁷ and juicier, but not as suitable for storage.

Dried onions are usually made from white or yellow onions with a high solids content (18-20% or higher) and ideally have 4% residual moisture. 8-10 kg of raw material yields 1 kg of dried onions. ¹¹ Winter onions (or spring onions or scallions) can also be dried (as mentioned above), but the dehydrated product is clearly labelled as a product made from spring onions.

Industrial production

The most commonly used modern drying methods for onions are sun drying or solar drying, convective air drying, solar greenhouse drying (GHD) and infrared drying. ²⁰

For classic hot air drying, the onions are stored in special tanks for 48 to 72 hours after harvest. These are heated with hot air (38 °C) so that the onions are easier to peel. After the onion roots have been removed, the onions are washed in a high-pressure cleaner and placed in a bath of chlorinated water to reduce bacteria to a minimum. The onions are then cut into thin slices by machine. Drying takes place on belts with hot air in several steps: first at hot temperatures (82-104 °C) to reduce the moisture content from 83% to 25%. Then drying takes place at lower temperatures to a moisture content of 4-6%. After drying, the onions are transported to be milled. In the mill, the skin of the onion pieces is first removed by blower. Finally, the onions are cut, chopped, ground or granulated before being packaged. ¹⁷

Freeze-dried onions are produced using the same process as freeze-dried herbs. The chopped onions are cooled to -18 °C using liquid nitrogen. In a vacuum, the resulting ice turns directly into a gaseous state (water vapor) and can be easily sucked out. Although this technique is more expensive, it ensures that the product retains its structure, natural color and flavor even when stored for a long time. ¹⁰

Further information

The onion ( Allium cepa ) belongs to the genus leek ( Allium). In the botanical sense, when referring to onions, it is always necessary to clarify whether it is Allium cepa or a plant part (a possible form of the storage organ of a plant).

Alternative names

Dried onions are also called dehydrated or dried onions, onion flakes or dried onions. In English they are called dehydrated onions or dried (dry) onions.