You can dehydrate onions to store them for a long time and use in seasoning or as snacks. The methods involve browning the onions at room temperature or drying them in an oven or dehydrator. The processes are quite simple, but each of them has specific steps.
Method 1 of 3: Tanning Onions to Preserve
Step 1. Choose strong flavored onions
Light onions don't taste so good. So, to tan the onions or dehydrate them, it is better to opt for spicy, strong-flavored onions.
- As a general rule, lighter onions are large and have paper-smooth rinds that are easy to peel off. When cut, these onions are very moist and their rings are thick.
- Stronger flavored onions are noticeably smaller in size and tend to have thicker skins. When cut, your rings will also be distinctly thinner and you will likely feel your eyes watering.
- Lighter onions will last, when dried or tanned, only a month or two at the most. On the other hand, the strongest onions can last an entire winter if stored correctly.
- The components that cause eye tears when slicing stronger onions also help to slow down the rotting process.
- See the strongest types of onions.
Step 2. Remove the sheets
Cut the wrinkled onion leaves with kitchen scissors and carefully clean the roots, removing any impurities.
- This step is only necessary if the onions have just been harvested. If you're buying onions at a market or grocery store, they're probably already clean.
- Be aware that onions should only be harvested when the plant's leaves begin to weaken and wither, indicating that the vegetable has stopped growing. Only fully ripe onions should be tanned for storage.
- Note also that the ideal is to tan or dehydrate the onions right after harvesting them, for better results.
Step 3. Transfer the onions to a warm, protected place
Arrange the onions in a single layer on a counter with temperatures between 15 and 27 degrees Celsius.
- Let the onions brown at this starting point for a week.
- If the outside temperature is still hot and dry and there is no risk of animals touching the onions, you can leave them in the garden for the first few days. However, you will need to store them in a covered location.
- Be careful when stirring the onions. They can be damaged if they hit each other hard. Also avoid touching them at this early stage.
- Do not leave onions in direct sunlight as this could cause uneven dehydration.
Step 4. Consider browning the onions in braids
You can finish browning the loose onions or braiding them.
- Braid the onions, joining them and removing all leaves except the three youngest. Tie or braid these remaining leaves with the other onions that are browning and hang them upright to finish the process.
- This is a matter of personal preference or space. According to some studies, onions will not do better or worse because they are braided or separated.
- Let the onions brown in this way for 4 to 6 weeks.
Step 5. Cut off the ends
During the process, you should prune the ends two or three times as the stems shrink. Cut off the remaining ends of the onions when they are fully browned. Roots must also be eliminated.
- As noted above, cut the ends of the onions two to three times during the process.
- When the onions have finished drying/daring, remove the ends completely.
- After the first two weeks of dehydration, you should use scissors to remove about 0.6 cm from the root of the onions.
Step 6. Store the onions in a cool, dry place
During winter in places with more severe weather, you can store them, for example, in the basement.
- Place onions in a canvas bag, wooden bucket, or perforated cardboard sheet. Do not stack the onions, leaving space for good air circulation.
- At a temperature of 0 degrees Celsius, stronger-tasting onions can last between 6 to 9 months, while lighter onions last between 2 weeks and a month.
Method 2 of 3: Oven Dehydration
Step 1. Preheat the oven to 70 degrees Celsius
Prepare two or more flat pans with parchment or parchment paper (oven resistant).
- On average, you will need two molds for each onion you want to dehydrate by this method. If dehydrating only one onion, prepare two molds. If you're going to dehydrate two, make four molds, and so on. It's better to have plenty of room than lacking.
- Do not let the temperature exceed 70 degrees Celsius during the process. If the oven temperature exceeds that point, you may end up burning the onions instead of dehydrating them.
- The trays used should be about 5 cm narrower on the sides than your oven, to allow air circulation.
Step 2. Cut the onion into thin slices
The roots, tips and husks must be removed and then the onion must be chopped into rings of 0.3 to 0.6 cm.
The easiest way to cut onions is with a hand slicer. If you don't have one, cut the onions as thin as possible with a sharp kitchen knife
Step 3. Spread the onion rings on the shapes
Transfer the onion rings to the already covered molds, in single layers.
Do not stack the rings as this will slow down the process and unevenly dehydrate the onions. This could be a problem in the future if undried onion pieces are kept with the rest
Step 4. Dehydrate them in the preheated oven
Place the onions in the oven and let them dehydrate for 6 to 10 hours, stirring the molds as needed so they don't burn.
- If possible, keep the oven door half-open, with a gap of 10 cm so that its interior does not get too hot. By doing this, you can also place a fan at the entrance to the oven to facilitate air circulation.
- Keep about 7.5cm of empty space between the molds and between the highest grid and the top of the oven. It is necessary to maintain a high air circulation.
- Keep an eye out for onions when they are finishing dehydrating, as they may end up burning if they go too far. If burnt, onions will deplete their flavor and nutrients.
Step 5. Break the rings when they are ready
At the end of the process, the onion rings will be brittle and can be broken by hand. Make onion flakes this way.
- To form the flakes, simply break the rings with your hands. To make onion powder, place the rings in a plastic bag and roll them over a rolling pin.
- You can also leave the rings unbroken, but keep in mind that they are already quite brittle and can break easily.
Step 6. Store in a cool, dry place
Place the onion flakes in an airtight container and store them in the pantry or other such location.
- If stored under vacuum, dehydrated onions can last up to 12 months. In other conditions (with less air insulation), they should last between 3 and 9 months.
- Check the humidity. If you notice any signs of moisture in the container during the first few days of storage, remove the onions, dehydrate them a bit more, and dry the container as well, before putting it away again. Moisture can quickly spoil onions.
Method 3 of 3: Using the Dehydrator
Step 1. Prepare the onions
Onions should be peeled and sliced into 0.3 cm rings.
- Remove the tip, root and skins from the onion.
- Use a vegetable slicer to cut the onion as thin as possible. If you don't have one, use a very sharp knife and slice as thin as you can.
Step 2. Place the onions in the dehydrator tray
Arrange the onion slices in your dehydrator in a single layer, positioning the trays so as to favor air circulation.
- Slices should not be bunched together or touching. Leave them as spread out as possible.
- The trays should also be as far apart as possible from each other. Keep at least 5 or 7, 5 cm between them to maximize air circulation.
Step 3. Leave to dehydrate for about 12 hours
If your dehydrator has a thermostat, turn it on to 63° Celsius (145 F°) and allow the rings to dry.
If you have an older or simpler model that does not have a thermostat, monitor the progress of the process carefully. The time required may vary (more or less) by about one hour from the total indicated. Therefore, monitor the onions and temperature, using an oven-resistant kitchen thermometer to estimate the total time needed
Step 4. Store the onions in an airtight container
Keep them in a cool, dry place. Use them in your recipes or eat them alone.
- In a vacuum container, onions can last up to 12 months. In other conditions (with less air insulation), they should last between 3 and 9 months.
- Check the humidity. If you notice any signs of moisture in the container during the first few days of storage, remove the onions, dehydrate them a little more, and dry the container as well, before putting it away again. Moisture can quickly spoil onions.
- You can break the onions into flakes or powder if you wish.