Onions
Onions are everywhere in cooking.
They are often the first ingredient added to a cooked dish. Onions add a subtle sweet and umami taste to cooked foods.
They are a part of classic French mirepoix and regional variations of mirepoix; and are foundational in every cuisine. Without onions our food would not taste the same as we know it today.
Raw Onions
The flavor of raw onions is instantly recognizable. They are strong and pungent and work nicely with salads and cooked meat, as they balance well with salty and sour flavors.
Onions are part of the genus allium which includes garlic, leeks, and chives. These plants all share a characteristic pungent, strong, and sulfurous flavor. This flavor comes from a chemical defense mechanism to prevent animals from eating the plants. As the plant grows, it takes up sulfur from the soil and produces chemical irritants which are stored in the cell fluid.
The plants also produce an enzyme that is stored in a separate storage vacuole. When the cell is damaged by chopping or chewing, the enzyme and sulfur compounds mix, and chemical reactions begin to occur. These reactions release sulfuric compounds into the air and produce new compounds which give the allium its pungent taste and smell.
Cooked Onions
Cooking changes the flavor of onions.
When the pungent sulfuric compounds are heated, they convert into milder more savory and meaty flavored compounds. Cooking also releases the natural sugars, which produces sweetness.
When onions are sautéed in the presence of fat, the sugars begin to caramelize and produce more complex flavor and aromas. Onions have a unique ability to go from a harsh and pungent flavored plant when eaten raw to a subtle, meaty, savory, sweet, and rich flavor when cooked. This is why onions are so ubiquitous in cooking around the world.
Onions in the U.S.
There are two major categories of onions in the U.S., defined by season and harvesting methods.
Spring Onions
Planted in the fall and harvested next spring. These onions are milder in flavor and more perishable.
Spring onions have smaller bulbs and green leaves that are edible. They should be kept refrigerated.
Storage Onions
These are harvested in the Fall and are rich in sulfuric compounds, which give them a stronger flavor and larger bulbs.
They are drier than spring onions and will hold in a cool, dry place for several months. Common storage onions include: yellow, white, sweet, and red.
Types of Onions
Yellow/Spanish Onion
Large, rounded yellow bulbs
The most common onion in the U.S. They are very versatile and caramelize well. If a recipe does not specify, use this type of onion.
Sweet Onion
Range in color from white to yellow and can have a flattened appearance
Sweet onions vary in name by region (e.g., Vidalia from Georgia, Walla Walla from Washinton State, and Maui from Hawaii.)
These onions are grown in soil with low amounts of sulfur, so the resulting onion has a milder flavor. They can be used in salads or as a garnish and are great when you want a subtler raw onion flavor.
Red Onion
Large in size with reddish-purple skin
Red onions have a strong, spicy, and peppery flavor to them. They work well when you want to add pungency or color to your dish. They are often used in salads and as burger toppings, and can be pickled, roasted, or grilled.
White Onion
Medium to large in size and are globular in shape
These onions are popular in Mexican cuisine. They are strong but have less of an aftertaste. They go well in salsa, guacamole, ceviche, and tacos.
Green Onion
Long green leaves with a small white bulb
These onions are milder in flavor overall. The white bulbs and green leaves are all edible. They are used heavily in Asian and Mexican cuisines and work well sliced and added raw as a garnish.
Why do onions make you cry?
Onions have developed an effective defense mechanism to help protect them as they grow.
Certain alliums (onions, shallots, leeks, and chives) spew enzymes and sulfenic acid when their skin is broken, producing propanethial S-oxide: a potent airborne chemical. When it encounters the watery layer in your eyes, it breaks down into sulfuric acid.
How do you stop the tears?
Temperature
The reactions that produce the sulfuric compounds in onions are slowed by colder temperatures. Putting your onions in a freezer or refrigerator to cool them down before slicing can reduce the tearing effect.
It is important to note that storing them in the fridge long-term is not recommended, as they will deteriorate faster. Best practice is to store them in a cool, dry place. Once you have cut the onions, they should be stored covered and refrigerated.
Rinsing
As you cut the onions, storing them in cold water will help diffuse the sulfuric compounds and protect your eyes. This is also a good way to remove some of the pungent flavor when serving them raw.
Eye protection
Contact lenses or goggles (if you want to tap into your inner chemist) will help shield your eyes from the irritants in the air.