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.

Our preference is for processed food, in fact, whether that means barbecued beef or barbecue-flavored potato chips.

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:

3 tablespoons (5g) for quick sauces of small quantities, such as those for sautés and fricassees.
5 oz. per quart (150g per liter) of fresh water destined to become a light and clear broth, such as a stock or a bean broth.
10 oz. per quart (300g per liter) of liquid destined to become a rich broth of some kind, as for most soups and stews.

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.)

  1. Aromatic vegetables practically never vary.

Behold, the Trinity:

Onion (the Father)
The most important one of all. Its sulphuric compounds render into sugars of the greatest complexity. Onion is sophisticated enough to stand alone; the next two vegetables are optional, strictly speaking.
Carrot (the Son)
The sweetest of the three, with a completely neutral flavor. Carrot has a nicely fulfilling effect. Without it, soup broths especially can seem like they lack something.
Leek (the Holy Spirit)
In addition to its metamorphic astringent compounds, shared by all members of the onion family, leek possesses a special, enriching flavor all of its own.

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:



These mild, red onions work especially well for quick sauces, as their relatively sweet profile renders just that much more quickly. Shallot is the classic aromatic in sautés and fricassees.



Another member of the onion family. A couple of split cloves per quart (liter) will yield a mildly meaty sensation, similar to the effect of leeks. I add them all the time when cooking beans and lentils. The longer they cook, the more subtle their presence (which is the whole idea behind garlic confit.)



This isn’t an aromatic at all. It doesn’t even belong in this article. I include it only because celery, and not leek, is what constitutes the third part of the classic trinity of aromatics, known to Monsieur le Chef and his crowd as mirepoix.

Many quirks in traditional restaurant cooking can be explained through some practical result or other. This isn’t one. Celery simply yields nothing to a simmering broth. Try it for yourself, sometime, with just a pan of water. The cooking aroma will be nice, but no flavor will impart, even though the celery itself will have lost everything in the process. It’s as if the vegetable’s essence was completely volatile.

Classical cooking, in its purest form, is philosophy, something in other words that imperfectly correlates with experience. Every branch of thought is like that, from Freudian psychology to modern architecture. They produce results, but they seem to fail just as frequently in the final analysis.

Traditions often serve simply to reassure both client and practitioner. Monsieur le Chef, for one, is ultimately bound by the exigencies of his bizarre clientele.

Home cooks have only their own tastes to follow, happily.

So save your celery for the salad.


  1. 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.

For quickly cooking sauces (sautés, fricassees), mince aromatics, since vegetables yield more flavor, more quickly, the finer they are cut.
For light broths (stocks and bean broths), chop aromatics into roughly one-inch pieces, since the hour(s) that they simmer will extract all that they have to give, anyway, and they’ll be easier to remove from the final result.
For rich broths (soups and stews), slice or dice aromatics neatly into bite-sized pieces, since the vegetables often do double-duty as garnish (garnish being the vegetables and other ingredients that populate a final dish).

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.

  1. 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.

Don’t bother to pre-cook aromatics for light broths like stocks, the whole point of such preparations being a delicate final result. Just chop your vegetables and put them straight into the pot.

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).

  1. 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.

Guided by Whim, Not Recipe
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