PHOTOGRAPHY BY JOHN COX
Chef secrets for making the most of the onions in your larder
I remember the first time I touched an onion. It was 1998, I was 17 and had literally just stepped into my first professional kitchen job. The chef pointed to a 50-pound bag of onions and said, “You can start by peeling those.” Peeling an onion may be a straightforward task for some people, but I had never even laid a hand on an onion. My mother has an aversion, bordering on an allergic reaction, to alliums in every shape and form. She detests the smell and flavor and had banished them from her kitchen long before I ever entered the picture.
Yet there I was, an aspiring teenage cook, eager to please the chef who had just hired me. I lugged the bag up onto the prep table and wrestled through the thick plastic netting with a dull knife that was hanging on the wall. I half cut, half bludgeoned the outer peel, pulling at the yellow flesh with my fingernails. By the second onion, my eyes were welling with tears and stinging. I tried to wipe away the tears with the back of my hand and that only exacerbated my condition. I clenched my eyes shut and felt my way across the kitchen and out the side door, thinking that my mother might have been right— onions really were evil!
The onion’s dark magic is actually a sophisticated defense mechanism, stemming from an enzyme called alliinase. As soon as the skin of the onion is broken and cells of the flesh are damaged, the enzyme is released and comes in contact with an odorless compound called isoalliin. This convergence creates a new volatile compound called 1-propenyl sulfenic acid that is in turn quickly converted into thiosulfinates and thiosulfonates. You would recognize these as the pungent odor and sharp flavor of raw onions. At the same time, another reaction is creating propanethial-S-oxide, or PSO—the compound responsible for making you tear up. As soon as your knife cuts through the skin of an onion, you unleash a powerful weapon biologically engineered to protect the tender bulbs. Small wonder both home cooks and professional chefs turn away from the plain jane of onions, the yellow onion, to the promise of a sweet Vidalia or Maui.
When it comes to developing a deep savory base for your recipe, more crying equals better results.
Historically, having onions in the larder was often a matter of life and death. Sailors on long voyages were expected to bring their own supply of onions because they were one of the few sources of vitamin C that would last for the duration of an open ocean crossing. Before this became common practice, thousands of sailors died of scurvy. Onions were also a staple for pioneers settling the West, and were one of the food staples for any covered wagon train. During the Civil War onions were such an important part of the troops’ diet that General Ulysses S. Grant stopped the forward progress of an entire army until a shipment of onions was delivered.
There are hundreds of varieties of onions to choose from, but generally globe onions can be classified into two categories, pungent and mild (also called sweet). Onions grown in less sulfurous soils have less alliinase, making them sweeter and less offensive in their raw state. Some onions known for being particularly mild and sweet, such as Vidalia or Maui, are created by growing sweeter cultivars in soil that is naturally low in sulfur. Typically, the mild varieties are large in size, have thick rings and paper skin that sometimes falls right off the bulb. The more pungent onions are smaller in size with tighter rings and skin. The other major difference is the type of storage required. Mild onions are best eaten within a few weeks of being harvested while pungent onions can be cellared for up to a year. The reason for this is that the same sulfurous tear-jerking compounds found in pungent onions act as a natural preservative. Because of this, sweet onions are highly seasonal and best in early summer when they are plentiful, while pungent onions can be found year-round.
You might wonder why, if onions can be grown sweeter and less tear jerking, farmers don’t just do it that way all the time. Why not just always buy sweet onions? The answer lies in the same biological defense mechanism. PSO, that little compound that makes you feel like you are under a teargas attack, transforms into something incredible when heated. The new compound is called 3-mercapto-2-methylpentan- 1-ol (MMP). This reaction, first formally documented by science in 2004, but surely recognized by cooks for hundreds of years, creates umami, that incredible fifth flavor, found in fermented products and roasted meats. MMP is water soluble and the best way to understand its importance is to try a spoonful of classic French onion soup. Raw sweet onions have less PSO, which means less MMP when cooked.
As a cook, it’s critical to understand that the more PSO you start with, the more MMP you will end up with. But it’s not simply a question of buying pungent onions; it’s also a matter of technique. In fact, many cultures finely chop onions, sometimes in combination with other ingredients such as peppers or celery, into a paste before using them. From the sofrito used as a base in Spanish and Portuguese dishes to the onion purée used prolifically in Indian cuisine and the omnipresent mirepoix of classic French recipes, finely chopped or puréed onion can be found in kitchens around the world. Whether you finely chop the onions with a knife, pulse them in a blender, crush them with the back of a pan or run them across a grater, the goal is to damage the onion cells as much as possible before applying them to heat. In other words, when it comes to developing a deep savory base for your recipe, more crying equals better results.
Now, if you want a perfectly sweet slice of onion on a sandwich, or a crisp ribbon of mild onion running through a ceviche, you want to take the opposite approach.
Few kitchen skills serve to separate the professionals from enthusiasts as quickly as slicing an onion. The trained kitchen mercenary makes quick work of slicing an onion. With a quick turn and two swift slices the root and head of the bulb are severed from the body. A shallow swipe with the tip of the knife releases the papery skin that peels away easily, leaving a perfectly clean bulb. The onion is then sliced in half across the rings and laid flat side against the cutting board. Curling the control hand into a gnarled claw, the chef will stabilize the onions while sliding the blade of the knife against the knuckle of their index finger. Once in position the chef unleashes a barrage of slices so acute and adept that the knife appears to leave the onion undamaged. Only when the chef makes the final cut does the bulb collapse into a pile of nearly transparent threads.
Not only do weathered chefs make this flourish of knife skills look effortless, they also rarely even deign to glance at the cutting board or razor-sharp blade flashing across their fingertips. All this, and seldom is a single tear shed. It turns out when your knife is razor sharp, the blade does little damage to the cells of the onion and, in turn, it doesn’t release the noxious fumes of PSO, resulting in a milder onion and more delicate flavor.
I can’t remember what recipe I was peeling that 50 pound bag of onions for. More likely than not, it was a task to keep me out of the way of the sharp knives and skilled cooks.
While onions can no longer be considered a matter of life and death, they are clearly one of the most important ingredients in any chef’s repertoire. Personally, I can’t even imagine a kitchen without any onions. There is something transformative about the lowly bulbs. What other ingredient can be simply combined with water, simmered for hours and slowly emerge as a savory, complex, amber syrup? From the crisp bite and fresh sweetness of a slice of raw onion garnishing a burger to the decadent smooth paste of caramelized onions, there are few more fundamental yet versatile ingredients. Taking the time to understand each onion variety and learning how cutting and heating transform their flavor are important lessons for any cook, so sharpen your knives and get your tissues handy.
RECIPE: John Cox
Spread on toast. Use in salad dressings and glazes. Drizzle on cheese or vegetables.
Caramelized Onion Tart
RECIPE: John Cox
Onions are clearly one of the most important ingredients in any chef’s repertoire.