Sometimes I wished I lived in another time. I wouldn’t actually want to spend too much time in late nineteenth-century England, but it would be fun to be there long enough to buy onions from an Onion Johnnie. Starting in 1828, when there was a bumper crop, some Breton farmers from the area around Roscoff would, at the end of summer, cross the channel to Plymouth with a few tons of onions and spend the remainder of the year selling them door to door.1 They would rent space in a barn to store the onions, and before going out to sell them, each farmer would braid the onions into strings so that they would be easier to transport. The thought of buying a string of pink Roscoff onions from a farmer at my door is just so neat.
Recorded history of the onion dates back to around 3000 BCE. The cultivation of onions is thought to have begun in India around 600 BCE, and there are Greek and Roman writings about onions from a couple centuries later.2 The exact date that onions were introduced to French soil is not known, but it was probably long before the start of the Common Era.
The use of onions is quite common in even the earliest of French cookbooks, a practice that continues to today. (From my research of French recipes, it seems that shallots, another member of the lily (Liliaceae) family and Allium genus, may actually be called for more often than onions. Or maybe not; they are both used quite often.) With a total yield of 484,000 metric tons3 and a population in 2005 of 60,656,000 people,4 the per capita consumption of onions by the French population was just under 8 kilograms per person,5 which is slightly higher than the world average.6 (Libya has the highest annual per capita consumption of 30.3 kilograms.)7 Other than starring in the occasional soup or tart, onions tend to show up as a bridesmaid instead of the bride in French cooking.
I’ve always thought that an onion consisted of a number of layers of oniony stuff inside a skin with a root at one end and a stem at the other. With a little research I’ve found that onions don’t have layers. A typical mature onion has two dry skins covering four swollen sheaths grown from bladed leaves. These in turn enclose three or four swollen bladeless bulb scales. In the center are five leaf initials with blades.8 Go figure.
What I find more fascinating is that although there are thousands of onion varieties, there are essentially no more wild onions in existence.9 Those thousands of varieties can be divided into two categories: fresh onions (sometimes referred to as spring or summer onions) and storage onions (sometimes referred to as fall or winter onions). Fresh onions are generally available from March to August. Fresh onions have thin, light-colored skins. Raw, they typically taste sweeter and milder than storage onions due to their higher water content. This higher water content also makes them more susceptible to bruising. Storage onions are generally available from August to April. They have thick, dark, papery skins that make them easier to peel. Storage onions typically have a more intense flavor than fresh onions due to their higher solids content. Both fresh and storage onions come in three basic colors: white, yellow, and red.10
Different onion varieties require a different day length in order to make a bulb. Long-day varieties set bulbs when they receive 15 to 16 hours of daylight. Short-day varieties set bulbs when they receive about 12 to 13 hours of daylight. Intermediate-day varieties fall in between.11 Onions grow in latitudes ranging from 5 to 60 degrees, so a wide range of day length is available.12
It turns out that the term “sweet onion” is not much more than that. There are no government regulations as to which onion can be called sweet and which cannot. And it is not uncommon for storage onions to contain more sugar than sweet onions, which are usually fresh onions. Sweet onions tend to be higher in water content, lower in solids, and lower in pyruvic acid level. The onion’s pungency is generally relative to its pyruvic acid level. Also affecting sweetness are sulfur-based peptides, thiosulfinates, and alkenyl cysteine sulfoxides. The ones you smell and taste the most are thiosulfinates.13
Genetic varieties, horticultural practices, soil type, and climate will influence the concentration of sugars and sulfuric compounds inside an onion bulb. Typically, the short-day variety available during the spring and summer will accumulate more water and produce a bulb with a lower concentration of sulfur compounds. Under the right growing conditions, these varieties will result in an onion where the sweetness in a raw onion can be perceived. In contrast, most intermediate and long-day varieties take on less water and have a higher concentration of the sulfuric compounds, which mask the sugars. But when heat is applied, as it is in cooking, the sulfur compounds dissipate and the sugar is again perceived.14
All onions, no matter which variety, need to be “cured” after harvesting. It is during curing that the onion’s papery skin forms and the stem shrinks to seal the onion bulb.15 For field curing, the onion bulbs are pulled from the soil and set in rows. Their tops partially cover the bulbs to help prevent sunburn and prevent bulb damage. The onion bulbs are left in this manner until the tops wither. Once this happens, the tops are cut off about an inch from the bulb. Field curing can take two to three weeks if the temperature is between 24 and 27 °C and the relative humidity is less than 60%.
Onions can also be cured in mesh bags or trays designed to provide proper ventilation. This method is safer than field curing. In addition, if ventilated with air between 29 and 32 °C, the curing period can be reduced to 4 or 5 days.
Depending on the type of onion and the curing method employed, onions can be stored for up to 8 months. They should be stored in a well-ventilated, dry, refrigerated area. If there is too much humidity, greater than 60%, the onions are susceptible to mold and rot.16
As of 2005, the world’s largest producer of onions, producing about one-third of the total world production, was China. India, the country in second place, produced slightly more than one-third as much as China. France came in about 25th place with a total production of about 432,000 metric tons. During that same period, France imported about 95,000 metric tons and exported 43,000 metric tons. (I wonder how many of the exported onions were the result of the few remaining Onion Johnnies?)
The most common question I get when I teach people how to cut onions into various shapes is “How do I keep from crying when I cut onions?” Maybe people should first ask “Why do onions cause me to cry?” The answer to the second question comes from Dr. Irwin Goldman at the University of Wisconsin:
When an onion is cut, the enzyme alliinase begins to react with the substrates known as Alk(en)yl-L-Cysteine Sulfoxides (ACSO). One of these ACSOs is called 1-propenyl L cysteine sulfoxide. When it reacts with alliinase, the reaction produces 1-propenesulfenic acid, pyruvic acid, and ammonia. The 1-propensulfenic acid then reacts with an enzyme called Lachrymatory Factor Synthase, which generates propanethial sulfoxide. This compound reacts with the nerve cell membrane of the eye to form sulfuric acid, and causes tearing.17
So how do you avoid contact with propanethial sulfoxide when you cut onions? I recommend four mitigating options: chill the onion thoroughly before slicing; use a very sharp knife; slice, not chop, the onion; and work in a well-ventilated space. Some people claim that the best solution is wearing contact lenses that cover the cornea’s autonomic motor fibers that in turn activate the lachrymal (tear) glands. Others suggest wearing swimming goggles, which provide the same function without a visit to the optometrist.
How should onions be peeled and sliced? I’m not going to give instructions for that here, but you can download a chapter from my book that explains the process.
The onion recipes that accompany this brief article run the gamut from recipes where onions are the principal ingredient to those where onions are just one of the major ingredients. There’s the usual assortment of soups, tarts, flans, and a few surprises, too. All of the recipes should work with whatever onions are available when you choose to try them. Enjoy.