Onions: Peeling Back The Layers
ivvga executive director kay pricola
This time of year, we know we live in an agricultural area simply because of the odor. That familiar smell signals the start of onion harvest. So, let’s spend a time on that all-important cooking ingredient, the onion.
The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Its close relatives include the garlic, leek, chive, and Chinese onion.
Common onions are normally available in three color varieties. Yellow or red onions (called brown in some European countries), are full-flavored and are the onions of choice for everyday use, with many cultivars bred specifically to demonstrate this sweetness (Vidalia, Walla Walla, Cévennes, "Bermuda and our favorite Imperial Sweets.). Yellow onions turn a rich, dark brown when caramelized and give French onion soup its sweet flavor. The red onion (called purple in some European countries) is a good choice for fresh use when its color livens up the dish; it is also used in grilling. White onions are the traditional onions used in classic Mexican cuisine; they have a golden color when cooked and a particularly sweet flavor when sautéed. IVVGA has an isolation program for onion seed to preclude cross pollination. We will feature a story on that in the future.
While the large, mature onion bulb is most often eaten, onions can be eaten at immature stages. Young plants may be harvested before bulbing occurs and used whole as spring onions or scallions. When an onion is harvested after bulbing has begun, but the onion is not yet mature, the plants are sometimes referred to as "summer" onions.
Additionally, onions may be bred and grown to mature at smaller sizes. Depending on the mature size and the purpose for which the onion is used, these may be referred to as pearl, boiler, or pickler onions, but differ from true pearl onions which are a different species. Pearl and boiler onions may be cooked as a vegetable rather than as an ingredient and pickler onions are often preserved in vinegar as a long-lasting relish.
Onion powder is a seasoning widely used when the fresh ingredient is not available. It is made from finely ground, dehydrated onions, mainly the pungent varieties of bulb onions, and has a strong odor. Being dehydrated, it has a long shelf life and is available in several varieties: yellow, red, and white.
Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may also be used as a main ingredient in their own right, for example in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or eaten raw in salads. Their layered nature makes them easy to hollow out once cooked, facilitating stuffing them, as in Turkish sogan-dolma.
Onions pickled in vinegar are eaten as a snack around the world, and as a side serving in pubs and fish and chip shops throughout the United Kingdom and the Commonwealth. They are part of a traditional British pub's ploughman's lunch, usually served with crusty bread, English cheese, and ale. I must mention the “blooming” onion, a hit at many American grills.
Similar to garlic, onions can show an additional color – pink-red – after cutting, an effect caused by reactions of amino acids with sulfur compounds.
Onions are toxic to dogs, cats, guinea pigs, and many other animals. They are not to humans, but some people suffer from allergic reactions after handling onions. Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating, and anaphylaxis. Allergic reactions may not occur when eating cooked onions, possibly due to the denaturing of the proteins from cooking.
Freshly cut onions often cause a stinging sensation in the eyes of people nearby, and often uncontrollable tears. This is caused by the release of a volatile gas, syn-propanethial-S-oxide, which stimulates nerves in the eye. This gas is produced by a chain of reactions which serve as a defense mechanism: chopping an onion causes damage to cells which releases enzymes called alliinases. These break down amino acid sulfoxides and generate sulfenic acids. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the lacrimatory factor synthase, producing the syn-propanethial-S-oxide. This gas diffuses through the air and soon reaches the eyes, where it activates sensory neurons. Lacrimal glands produce tears to dilute and flush out the irritant. Yes, too much science, again.
Eye irritation can be avoided by cutting onions under running water or submerged in a basin of water. Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb. Refrigerating the onions before use reduces the enzyme reaction rate and using a fan can blow the gas away from the eyes. The more often one chops onions, the less one experiences eye irritation. In the Pricola household, neither of us surfer any long because onions are on the menu almost every meal.
Onions are best cultivated in fertile soils that are well-drained. Sandy loams are good as they are low in sulphur, while clay soils usually have a high sulphur content and produce more pungent bulbs. Onions are a cool-weather crop and can be grown in USDA zones 3 to 9 Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow Imperial Valley is classified a zone 9B which puts us in the zone, but barely. Onions are harvested here by mid-June due to higher heat levels and the increased humidity.
Onions may be grown from seed or from sets. For commercial purpose here, onions are grown from seed. Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need a great deal of water once established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if they will be kept in storage, they should be harvested after the leaves have died back naturally. In dry weather, they can be left on the surface of the soil for a few days to dry out properly, then they can be placed in nets, roped into strings, or laid in layers in shallow boxes. They should be stored in a well-ventilated, cool place such as a shed.
Cooking onions and sweet onions are better stored at room temperature, optimally in a single layer, in mesh bags in a dry, cool, dark, well-ventilated location. In this environment, cooking onions have a shelf life of three to four weeks and sweet onions one to two weeks. Cooking onions will absorb odors from apples and pears. Also, they draw moisture from vegetables with which they are stored which may cause them to decay. My advice is to store them separately.
Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but reduces their shelf life. Sweet onions can be stored refrigerated; they have a shelf life of around 1 month. Irrespective of type, any cut pieces of onion are best tightly wrapped, stored away from other produce, and used within two to three days.
In 2016, world production of dried onions was 93.2 million tones, led by China and India producing 26% and 21% of the total, respectively. Here in 2017, we harvest from 13,087 acres of onions valued at $79,069,000. So, as you drive the country road, note the smell of onions. It is the crop of the month-and for a couple of months.