Foundations

More Than Just Mirepoix

How aromatic vegetables like onion, carrot and leek make everything delicious.

The difference between chicken-flavored water and chicken soup is that the latter has onions.

If that sounds simplistic, well then, you’re in for a delightful surprise. True deliciousness really is a basic thing.

But what is delicious, exactly?

It isn’t “flavor,” the kind of thing you get from herbs and spices, or truffles from the Périgord. It’s something more fundamental, a sensation on your palette that signals the presence of certain molecular chains involving amino acids, sugars and fats. The more complex those compounds, the greater the sensation of deliciousness. And that brings us to that peculiar adaptive technology of our species, known as cooking.

We have homo Erectus to thank for that, evidently, who about one million years ago began roasting meats and probably root vegetables.

Human anatomy underwent a significant transformation, as a result. Material and energy once devoted to digestion was diverted instead towards an increasingly sophisticated nervous system. Human beings became smarter, more sensitive, and more agile, all because we could get more out of everything we ate.

Heat has a way of pre-digesting foods. It softens rigid fibers, for example, unlocking a vegetable’s nutrients. The process isn’t simply destructive. Heat also augments starches, changing them into sugary compounds, one result being the extraordinary sweetness of a roasted sweet potato.

So whereas chimpanzees still spend their days foraging for precious figs (which they eat even unripe), we humans effortlessly transform any number of roots and tubers into “fruits,” nutritionally speaking, with readily digestible sugars and fibers.

Our preference for cooked foods is universal and transcultural. The Japanese, for instance, may quite like raw fish, but sashimi and the like make up only one part of their national cuisine. In any case, they frequently consume their morsels of raw fish with mouthfuls of cooked rice doused in fermented soy sauce.

Our preference is for processed food, in fact, whether that means barbecued beef or barbecue-flavored potato chips. We love fermented meats, and macerated fruits, and the taste of rendered fats. We love vegetables wilted with salt, and fish that has been “cooked,” after a fashion, in citrus juice.

It isn’t that the flavors of processed foods are more delicious from an objective point of view, it’s that we’ve evolved to notice and appreciate any evidence that processing has occurred.

What we recognize as the texture of cooked meat, for example, is a plasticization that occurs after heat has unraveled proteins and caused them to tangle back together arbitrarily.

Likewise, we generally prefer the complex sugars of cooked onion to the sulphureous compounds from which they came.

The longer we cook the vegetable (up to a certain point), the more complex that things become. Eventually, heat succeeds in even browning what it cooks, resulting in arguably the most delicious flavors of all.

Over the millennia, cooking became an art of composition, of course, one in which soups and sauces and other concoctions reveal novel ways of blending complex compounds from a variety of sources.

And that brings us back to aromatics.

Adding a little onion to a simmering broth imbues the liquid with the vegetable’s sugars and aromas, gradually augmented by the simmering heat.

Cooking that onion in a little fat beforehand makes the vegetable’s qualities even more pronounced. (And the fat itself makes the final dish just that much richer.)

As for how exactly to use an aromatic vegetable like an onion, that depends on the preparation—although any decision to make is a simple one, and the variations to consider are few.

Cooking is never complicated. If it seems that way, you’re probably looking at a recipe.

Aromatics: First Principles

1. Aromatic vegetables function anonymously.

They play the same role in your cooking as a bassoon does in an orchestra. Aromatic vegetables flesh out the timber of the final result, or signal subtle undercurrents.

You need only enough aromatic vegetables to fulfill their supportive role—never so much that they throw everything off-balance or draw attention to themselves.

I use the following:

Stocks and the like take smaller amounts of aromatics, relatively speaking, since the vegetables can easily overwhelm delicate broths made from mostly bones or legumes, leaving a chicken stock, for instance, tasting like carrot broth.

As for soups and the like, a fullness of flavor is the whole point. (The aromatics are also cooked beforehand, in most cases.)

2. Aromatic vegetables practically never vary.

Behold, the Trinity:

So, for every liter of water going into a chicken stock, I use 50g each of onion, carrot and leek, which comes to the 150g-per-liter that I recommend above.

(I use metric for everything, by the way.)

For every liter of liquid destined as a soup or stew, I use 100g of each vegetable, which comes to the 300g-per-liter that I recommended.

Sautés, with their minuscule quantities of aromatics, need only onion.

Three other vegetables deserve special mention:

3. The form of an aromatic vegetable is a function of the dish into which it goes.

That isn’t a decision you have to make.

Occasionally, you won’t have to bother at all with slicing or dicing: For broths involving beans, legumes or diced meat, which don’t easily separate from sodden pieces of aromatic vegetable, just split your carrots and onions, and leave a half-inch of the root of every leek intact, tying the vegetable at one end, in order to keep it from falling apart.

Keep in mind, finally, that vegetable pieces cook evenly when they are all essentially the same size and shape. The more briefly they cook, the greater the benefit of uniformity.

4. Whether to cook an aromatic vegetable before simmering it is a function of the dish into which it goes.

That isn’t a decision you have to make, either.

That leaves everything else.

Cooking diced aromatic vegetables in a little fat is a practically ubiquitous first-step in cooking. The longer the aromatics cook before any liquid is added, the sweeter and more complex they become.

A few minutes is sufficient for noticeable effect. Any length of time longer than fifteen minutes, on the other hand, seems to yield only diminishing returns.

So, aim for fifteen minutes, but take just a few minutes if that’s all you have (or what you feel like, in any case).

5. Aromatic vegetables never brown.

The sweetness and character of caramelization is opposite of what you desire in aromatics.

(Exceptions to that are cases in which a caramelized aromatic vegetable is the whole point, as in French onion soup.)

Cooking aromatics involves sweating, an unlovely term that signifies the opposite of searing.

Sweating gently softens and renders ingredients over low heat, using just enough fat to shield each morsel from the heat of the pan.

Sweating is what recipe-writers have in mind when they instruct you to cook onions until they are “translucent.”

Here’s what that looks like, by the way:

The appearance and intensity of the sizzle in that video is what you’re after with sweating. For longer intervals up to fifteen minutes, turn the heat down to the lowest setting that still produces the sound of sizzling, even if nothing is visibly evident.

It helps to have a good quality pan, which I describe in my article on Dutch ovens.

As for the fat itself, you need only enough to grease the pan—which is to say that the “two tablespoons” of butter or oil that recipes typically prescribe is ultimately arbitrary.

And that’s it.

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