Pickling is a popular way to preserve vegetables and extend their shelf life. The process involves soaking vegetables in a brine solution, usually made with vinegar, salt, and spices. Onions are a common vegetable used for pickling. However, raw onions can sometimes overpower the brine with their pungent flavor. This is why many recipes call for soaking the onions before pickling them.
Soaking onions serves a few key purposes:
- It reduces the harsh, tear-inducing compounds
- It mellows out the onion flavor
- It plumps up the onions for a better texture
Let’s explore why soaking is an important first step when pickling onions.
Reducing Harsh Compounds in Onions
Onions contain sulfur compounds called amino acid sulfoxides. When an onion’s cell walls are damaged, through chopping or slicing, these compounds mix with enzymes and create sulfenic acids. The sulfenic acids then quickly rearrange into syn-propanethial-S-oxide. This gas escapes from the onion and wafts towards your eyes, stimulating the lacrimal glands and causing tears.
Soaking onions allows these harsh compounds to leach out into the water before pickling. This makes the onions less likely to cause stinging, tears, and irritation when you eventually open up your pickled onion jar.
Key Compounds in Onions
The main sulfoxides present in onions are:
- Isoalliin
- Methiin
- Propiin
These sulfoxides don’t cause tears on their own. But when an onion’s cell structure is disrupted, the sulfoxides are converted through enzymes into irritating sulfenic acids and syn-propanethial-S-oxide.
Soaking slices this cell structure open while allowing the irritating compounds to leach away.
Length of Soaking Time
Most recipes call for soaking onions anywhere from 30 minutes to 1 hour. This gives enough time for the harsh compounds to diffuse into the water.
However, studies have shown that soaking for at least 5 minutes makes a noticeable difference. The more time you allow, the more the irritants can leach out.
One study published in the Journal of Food Biochemistry examined how soaking affects the levels of these sulfur compounds. They found that:
- 5 minutes removed 35% of sulfur compounds
- 10 minutes removed 50%
- 30 minutes removed 75%
So while 30-60 minutes is ideal, even a brief 5-10 minute soak will mellow the onion flavor and make them less tear-inducing.
Mellowing the Onion Flavor
In addition to making onions less irritating to cut and peel, soaking also removes some of the harsh and pungent flavor compounds.
Onions contain oils and sulfur compounds that give them their signature bite and piquancy. But you may not want an intensely strong onion flavor in your pickled vegetables.
Here are some of the main flavor compounds found in onions:
- Thiopropanal S-oxide – gives onions their tear factor
- Thiosulfinates – pungent, sulfur notes
- Cepaene – gives onions an intense flavor
- Lachrymatory factor – causes tearing and stinging
These oils and compounds can overpower the other flavors in a pickle brine. Soaking lets them leach away, leaving behind a more mellow and balanced onion flavor.
The end result is a pickled onion with a softened onion bite. The onion flavor comes through without being too spicy, harsh, or dominating.
Testing the Onion Strength
You can test if your onions have mellowed enough by tasting a small slice after soaking. If the onion still has a powerful burn, let it soak longer. The ideal is a softened flavor with the strong edge removed.
The soaking time depends on the strength of the original onion. 30 minutes is typically enough time to adequately mellow the flavor.
Plumping Up the Onion Texture
A final benefit to soaking onions is it plumps up their texture before pickling. This allows the onion slices to better absorb the brine solution.
Onions have a high moisture content around 85-90%. But most of this moisture is locked inside the onion’s cell walls. Cutting into an onion releases some of the moisture, seen as the weepy discharge when you slice an onion.
Soaking enables the moisture to hydrate the individual cells. Water gets trapped inside the cell walls through a process called osmosis. This gives a nice plump, juicy texture to the onion slices.
The swollen slices more readily absorb the flavors of the pickling brine. It also gives a pleasant crunchiness to the texture of the finished pickled onions.
If you don’t soak the onions first, the slices can turn out overly dry and shriveled when pickled.
Salt in the Soaking Water
Some recipes call for adding a bit of salt to the soaking water, about 1 teaspoon per cup of water.
The main purpose of salt during soaking is to help draw moisture out of the onions, causing them to take up more water and plump up. This enhances the effect of the soak.
Salt also begins to season the onions and brighten up their flavor. Just don’t use so much salt that it overly seasons the onions before pickling.
Pickling Brines Work Best on Soaked Onions
When onions are soaked first, it allows the pickling brine to better penetrate and cure the vegetable.
A good pickling brine needs a balance of flavors. The soak tames raw onion punch, letting the vinegar, salt, sugar, and spices come through.
Without soaking, the onions can resist absorbing the brine fully. Soaking almost pre-pickles the onions, so the flavors can then properly mingle during the curing process.
Here are some ways the soak improves the brining process:
- Plumped onions absorb flavors better
- The brine can directly season the vegetable
- Mellowed onions don’t overpower other flavors
- Onions and brine achieve an ideal balance of flavors
This results in a better distribution of flavors from the brine into the vegetable.
Firmer Texture
Soaked onions also tend to retain a firmer, crisper texture after pickling.
The hydrated vegetable holds up better to the pickling process. Onions soaked for an hour before brining were found to be less mushy and better maintain their crunch.
Other Vegetables to Soak Before Pickling
While onions are the most common veggie to soak, other vegetables can also benefit. Vegetables with a high moisture content and strong flavors are good candidates.
Some other vegetables that may be soaked before pickling include:
- Radishes – 30 minutes removes some harshness
- Cucumbers – at least 1 hour to pre-salt and crisp
- Cabbage – 30 minutes to soften leaves
- Green tomatoes – 1 hour to remove acids
The textures of these vegetables are also improved through soaking and swelling. Follow recipe instructions, as soak times vary.
Tips for Soaking Onions
Here are some tips for effective onion soaking:
- Peel onions first for better water penetration
- Slice onions fairly thin, about 1/4 inch
- Use cool or room temperature water
- Soak 30-60 minutes, tasting to test mellowness
- Drain onions well before brining
- Rinse if needed to remove slippery outer layers
Thinner slices give more surface area for the harsh compounds and flavors to leach out. Warm water can begin cooking the onions. Drain excess water before pickling so the brine flavors stay balanced.
Caution With Metal Bowls
Some recipes advise against using reactive metal bowls during soaking. Acids in the onions can react with metals like aluminum, copper, or cast iron.
Instead, use glass, ceramic, or stainless steel containers for onion soaks. Enamel or plastic bowls also work well.
Conclusion
Soaking onions before pickling improves their flavor, texture, and ability to absorb a brine. It mellows out harshness, reduces irritation, and allows the onion’s moisture to swell for a plumper, crunchier texture.
While an hour-long soak is ideal, even 5-10 minutes makes a noticeable difference. Test onions along the way to ensure their flavor is not still overpowering. Thinner slices in cool water allow the onion’s compounds to properly leach away.
Soaked onions pickle up nicely, integrating the brine flavors beautifully. Their texture also remains firmer compared to un-soaked onions.
Understanding the chemistry behind onion tears and harshness allows you to mitigate these effects through strategic soaking. The next batch of pickled onions you make will go down much more smoothly!
| Compound | Effect in Onions |
|---|---|
| Isoalliin | Sulfoxide compound, converts to irritating acids when onions cells are damaged |
| Methiin | Sulfoxide compound, converts to irritating acids when onions cells are damaged |
| Thiopropanal S-oxide | Gas that causes tearing and stinging sensation |
| Thiosulfinates | Sulfur compounds giving onions a pungent, spicy flavor |
| Vegetable | Recommended Soak Time | Benefits |
|---|---|---|
| Onions | 30-60 minutes | Reduces harshness, mellows flavor, plumps texture |
| Radishes | 30 minutes | Removes some sharpness |
| Cucumbers | 1+ hours | Crisps texture, pre-salts |
| Cabbage | 30 minutes | Softens leaves |