Category: Vegetables
🤔 What Is An Onion?
An onion is a versatile bulb vegetable that is one of the most fundamental ingredients in cooking around the world. It can be sharp and pungent when raw, but it develops a deep, savory sweetness when cooked, forming the aromatic flavor base for countless soups, stews, sauces, and roasts.
Quick Reference Card
| Condition | Ideal Storage | Duration |
|---|---|---|
| Whole/Unpeeled Onion | Pantry (cool, dark, ventilated) | 1-3 months |
| Cut/Peeled Onion | Refrigerator: 0-4°C (32-39°F) | 7-10 days |
| Frozen | Freezer: -18°C (0°F or below) | 6-8 months |
The Triple-S Method
Master the three essential steps for food success:
🛒 SHOP SMART: Selection Guide
- Choose firm, heavy onions with dry, papery skins.
- Avoid any bulbs that have soft spots, mold, or a noticeable scent.
- The neck of the onion should be tightly closed and dry.
Appearance
Look for a smooth, unblemished outer skin. Avoid onions with dark patches or any signs of sprouting, which indicate age.
Smell
A fresh, whole onion should have little to no smell. A strong onion odor from an unpeeled bulb could mean it is bruised or starting to spoil.
Texture
The onion should be rock-hard. Any softness or moisture near the neck is a sign of decay.
Common Varieties / Types
Different onions are best suited for different culinary tasks.
- Yellow Onion: The all-purpose workhorse. It is pungent when raw but becomes deeply sweet and savory when cooked, making it the standard for most recipes.
- Red Onion: Known for its beautiful deep-purple skin and flesh. It is milder and sweeter than a yellow onion, making it ideal for eating raw in salads and sandwiches.
- White Onion: Has a crisp texture and a sharper, more pungent flavor than yellow onions. It is common in Mexican cuisine and great for salsas or as a topping.
- Sweet Onion (e.g., Vidalia, Walla Walla): Has a higher sugar and water content, making it exceptionally sweet and mild. It is perfect for onion rings and eating raw.
📅 Seasonal Buying Guide
North America (USA/Canada)
Onions are harvested in late summer and fall. Due to their excellent storage capabilities, they are available with consistent quality year-round.
Europe
The main harvest is in late summer and autumn. Onions are a staple available throughout the year.
Australia/New Zealand
Onions are harvested in the late summer and autumn and are available year-round.
Tropical/Subtropical Regions
Onions are a global crop, grown and available consistently in all climates.
Seasonal Quality Variations
There is very little seasonal quality difference for consumers, as cured storage onions are designed to last for many months.
❄ STORE FRESH: Storage Guide
- Whole: Cool, dark, dry pantry for 1-3 months.
- Cut/Peeled: Refrigerator in an airtight container for 7-10 days.
- Key Tip: Do not store whole onions in the refrigerator.
Storage Method Details
Pantry: The best place for whole, unpeeled onions is a cool, dark, dry, and well-ventilated area like a pantry or cellar. Storing them in a mesh bag allows for airflow. Do not store them in plastic bags, which trap moisture.
Refrigerator: Storing whole onions in the fridge is not recommended as the humid environment can make them soft and cause them to spoil faster. However, once an onion is peeled or cut, it must be stored in a sealed container in the refrigerator.
Cured onions have very low moisture on their papery skin, which protects them from rot. A dark, dry environment with good airflow prevents them from sprouting or molding, allowing them to last for months.
Ethylene Production/Sensitivity
Onions are low ethylene producers, but do not store them next to potatoes. The gases and moisture from onions can cause potatoes to sprout prematurely.
Revival Techniques
If an onion has started to sprout, you can still use it. Simply cut the onion in half and remove the green sprout, as it can be bitter. The rest of the onion is fine to use, though it may have lost some of its potent flavor.
⚠ STAY SAFE: Food Safety Tips
- Max Time at Room Temp: 2 Hours (once cut)
Understanding Food Safety Rules
While onions have natural antimicrobial properties, they are still perishable once cut. The FDA advises that cut onions must be refrigerated in a sealed container within 2 hours to prevent bacterial contamination.
Reheating Methods
Onions are almost always an ingredient within a dish, which can be reheated.
Stovetop/Microwave
Dishes containing cooked onions, like soups or stews, can be reheated on the stovetop or in the microwave until thoroughly hot.
Date Labels Explained
Fresh onions do not have date labels. Judge their quality by their firmness and the condition of their dry outer skin.
Allergen Information
- Contains: None of the top 9 allergens.
⚠ Special Safety Considerations
The sulfur compounds in onions are what cause you to cry when cutting them. To minimize this, chill the onion for 30 minutes before cutting, use a very sharp knife, and cut near a vent or open window.
Pesticide Residue Information
The dry, outer papery layers of an onion are removed before eating, which provides a good barrier against pesticide residues. A quick rinse after peeling is still a good practice.
🧊 Freezing & Thawing Guide
Freezing Effects & Preparation
Freezing onions destroys their crisp texture, so they are not suitable for raw applications after thawing. However, they are excellent for use in cooked dishes as an aromatic base.
To freeze, simply peel and chop the onions to your desired size. The USDA states that blanching is not necessary. Freeze them in an airtight container or freezer bag.
Recommended Thawing Methods
There is no need to thaw frozen onions. Add them directly to a hot pan with oil to sauté for soups, stews, and sauces. They will release some water, so cook until it has evaporated.
Not Recommended
Thawing onions before cooking is unnecessary and can result in a mushy texture.
🔥 Cooking Information
Quick Cooking Reference
The way you cook an onion fundamentally changes its flavor, from sharp and pungent to deeply sweet and savory.
| Method | Heat | Time | Result |
|---|---|---|---|
| Sautéing (“Sweating”) | Medium-Low | 5-8 min | Soft, translucent, savory |
| Caramelizing | Low | 45-60 min | Deep brown, jammy, very sweet |
| Roasting | 200°C (400°F) | 30-40 min | Tender, sweet, browned edges |
Cooking Methods for Onion
Onions are a cornerstone of savory cooking.
Sautéing
This is the start of countless recipes. Cook chopped onions in butter or oil over medium-low heat until they soften and become translucent. This mellows their pungency and builds a savory foundation.
Caramelizing
To achieve a deep, sweet, jam-like result, slice onions and cook them very slowly over low heat with a little fat for 45 minutes or more. This process breaks down the complex sugars and is the key to dishes like French onion soup.
Roasting
Cut onions into wedges, toss with oil, and roast at 200°C (400°F). They will become tender, sweet, and delicious, perfect as a side dish for roasted meats.
📊 Nutritional Information
Average values per 100g (approx. 3.5 oz) portion
- High in: Vitamin C
- Good source of: Vitamin B6, Fiber, Antioxidants (Quercetin)
Onion (Raw/Fresh)
- Calories: 40 kcal
- Protein: 1.1g
- Fat: 0.1g
- Carbohydrates: 9g
- Fiber: 1.7g
Onion (Cooked/Prepared)
- Calories: 44 kcal (sautéed)
- Protein: 1g
- Fat: 0.2g
- Carbohydrates: 10g
- Fiber: 1.4g
Key Nutrients & Their Benefits
- Quercetin: Onions, especially red onions, are rich in this powerful flavonoid antioxidant, which has potent anti-inflammatory properties.
- Sulfur Compounds: Responsible for the onion’s sharp smell and health benefits, these compounds have been studied for their potential to support heart health.
- Prebiotics: Onions contain inulin and FOS, which are prebiotic fibers that feed beneficial gut bacteria and support a healthy digestive system.
Nutritional data is an estimate. Consult with a nutritionist for personalized advice.
🌎 Sustainability & Sourcing
Onions are a highly sustainable crop. They have a long storage life, which reduces food waste, and they can be grown in a vast range of climates, allowing for local sourcing in many parts of the world.
Buying onions from local producers helps to minimize their already low carbon footprint.
🔄 Substitutions & Alternatives
Shallots can be substituted for a milder, more delicate flavor. Leeks can replace onions as an aromatic base in soups and stews. Green onions or chives can provide a mild onion flavor as a garnish.
Onion powder can be used to add onion flavor when fresh onions are not available, but it will not provide the same texture or sweetness.
🔪 Recommended Tools
A very sharp chef’s knife is the most important tool for cutting onions; a sharp blade breaks fewer cell walls, releasing fewer of the compounds that make you cry. A mandoline slicer is excellent for creating paper-thin, uniform slices.
💡 Pro Tips
♻ Waste Reduction
Save the papery skins and root ends of your onions in a scrap bag in the freezer. They are packed with flavor and color and are a perfect addition to homemade vegetable or meat stocks (just strain them out before using).
✨ How to Revive It
If a cut onion has dried out slightly in the fridge, you can still use it for any cooked application. The cooking process will rehydrate it and it will still provide excellent flavor.
❓ FAQ
A: When you cut an onion, you break open its cells, releasing sulfur compounds. These compounds react to form a gas called syn-propanethial-S-oxide, which irritates your eyes, causing them to produce tears.
A: Chilling the onion for 30 minutes before cutting, using a very sharp knife, and cutting near a vent or an open flame can all help reduce the amount of irritating gas that reaches your eyes.
A: The cold, humid environment of the refrigerator can cause whole onions to become soft and moldy much faster than if they are stored in a cool, dark, dry pantry.
A: Onions release ethylene gas and moisture, which can cause nearby potatoes to sprout and spoil prematurely.
A: Sweet onions like Vidalias are sweet because they have a lower sulfur content (which makes onions pungent) and a higher water content, not necessarily more sugar than a yellow onion.
A: Yes, the green sprout is edible and tastes like a mild green onion. It’s a sign the onion is old, so you should cut the bulb in half and remove the sprout, as it can be bitter, but the rest of the onion is still usable.
A: Shallots are smaller, grow in clusters like garlic, and have a much milder, sweeter, and more delicate flavor than onions.
A: Cooking reduces some nutrients like Vitamin C, but it also increases the bioavailability of antioxidants like quercetin. Cooked onions are still very healthy.
A: Yellow onions are the all-purpose standard for cooking, as they develop a deep, savory sweetness. Red onions are milder and are often preferred for raw applications, though they are also delicious when grilled or roasted.
A: After chopping, rub your hands on a stainless steel object like your sink under cold water. The steel can help to neutralize the sulfur molecules that cause the odor.