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The Food Lab: How to Make Creamy Vegetable Soups Without a Recipe
It's time for another round of The Food Lab. Got a suggestion for an upcoming topic? Email Kenji here, and he'll do his best to answer your queries in a future post. Become a fan of The Food Lab on Facebook or follow it on Twitter for play-by-plays on future kitchen tests and recipe experiments.
Editor's Note: All month, the soup's on, with over a dozen new recipes coming at you for everything from simple 15-minute meals, to updated homemade versions of the canned classics you loved as a kid, to all-dayers that are hearty enough to eat like a meal. Check out all the recipes right here, and be sure to come back—we'll be updating all month!
When I was a totally green cook with my first serious restaurant job, working under Chef Jason Bond at what's now a landmark Boston restaurant, No. 9 Park, there were many moments when I learned a new technique or perfected an old one and said to myself, "holy crap, I just made this?" But the very first was when Chef Bond taught me how to make a creamy chanterelle soup (read: Campbell's cream of mushroom soup on tasty, tasty crack), sweating aromatics, sautéeing mushrooms, adding a good stock, and puréeing it all while emulsifying the mixture with fresh butter.
Like any great vegetable soup, the end result was something that tasted like a liquefied, purified, intensified version of itself—this soup tasted more like chanterelles than actual chanterelles. The magic lies in the way that aromatic ingredients can intensify and bring out other flavors, as well as the way in which liquids coat your mouth, giving more direct contact to your taste buds and olfactory sensors, and making for easier release of volatile compounds.
These days, there aren't too many vegetables in the world that I haven't made into a smooth, creamy soup, and there are even fewer that I've not loved*, but my experience has taught me something: that first process of making a chanterelle soup wasn't really just a recipe for chanterelle soup. It was a blueprint for making any creamy vegetable soup. You just need to break it down into its individual steps and figure out how to universalize them.
*Wait a minute, something doesn't make sense with that sentence. But you get what I mean.
Let's say, for instance, that I've never made a smooth carrot soup flavored with ginger and harissa, but I really like the idea. Here's how I'd go about it.
Step 1: Prepare Your Main Ingredient
The simplest soups can be made by simply adding your main ingredients raw and simmering them in liquid later on. When preparing this type of soup, all you've got to do is get your main ingredient ready by peeling it (if necessary) and cutting it into moderately small pieces. The smaller you cut, the quicker your soup will cook down the line.
There are times when you may want to boost the flavor of a main ingredient by, say, roasting or browning it. This is an especially effective technique for sweet, dense vegetables like sweet potatoes and squashes, or brassicas like broccoli or cauliflower, all of which intensify in sweetness with some browning. To roast your vegetables, cut them into large chunks, toss with some olive oil, salt, and pepper, set them in a baking sheet lined with aluminum foil or parchment paper, and roast in a 375°F oven until tender, with their edges tinged brown.
This works in two ways. First, the process of caramelization breaks down large sugars into smaller, sweeter ones. Second, enzymatic reactions that create simple sugars are accelerated with heat.
For this soup we're using carrots, and we aren't going to roast them, because I want the clean flavor of fresh carrots to come through.
Step 2: Choose Your Aromatics
Alliums—onions, leeks, shallots, garlic, and the like—are like the Best Supporting Actor of the soup pot. They're not there to steal the spotlight, but without them, your soup would be damn boring. Nearly every soup I make starts with either onions or leeks, along with some garlic or shallot (and sometimes all four!) cooked down in olive oil or butter.
Other firm vegetables such as diced carrots, bell peppers, celery, thinly sliced fennel, or ginger can work well in certain situations, but they tend to have a stronger impact on the finished flavor of the dish, so make sure that you really want them there. Make a carrot soup with just onions and it'll taste like carrot soup. Make a carrot soup with fennel or ginger, and it will taste like carrot-and-fennel soup or carrot-and-ginger soup.
For this soup we're going to use a blend of onion, leek, garlic, and ginger, flavors which blend well with harissa.
Step 3: Sweat or Brown Your Aromatics
Next big question: to sweat or to brown?
- Sweating is the process of slowly cooking chopped vegetables in a fat. You do it over moderate heat, and the goal is to get rid of some of the excess moisture within those vegetable, and to break down their cellular structure so that their flavor is released. With the case of alliums, there's another process going on: onion aroma is created when certain precursor molecules that exist within separate compartments in onion cells break out and combine with each other. Sweating an onion will break down cell walls, allowing this process to happen. The same holds true for garlic, shallots, and leeks.
- Browning starts out like sweating, but generally takes place over higher heat. Once excess liquid from vegetables has evaporated, the vegetables can begin to brown and caramelize, creating rich flavors, more sweet notes, and more complexity.
You might think that more flavor is always better, and thus you should always brown your vegetables, but more often than not, this browning can be overpowering, making soups too sweet or competing too much with the subtler flavors of your main vegetable.
For this soup we're sweating our vegetables in olive oil with no browning.
Step 4: Add Second-Level Aromatics Like Spices and Pastes
After your aromatics have sweated or browned, the next phase is your secondary aromatics, and it's an optional stage that's often omitted. If you like very clean, pure-tasting soups, jump ahead. If you like playing with flavors and spices, then you'll have fun with this step.
These are things like ground spices (say, curry powder, ground cumin, or chili powder), and moist pastes (like tomato paste, harissa, or chopped chipotle peppers in adobo sauce). These types of ingredients benefit from a brief toasting or frying in hot oil, which alters some of their constituents into more complex, more aromatic products, as well as extracting fat-soluble flavors so that they disperse more evenly into the soup.
Because ground spices have such a high surface area-to-volume ratio and most pastes have already been cooked, the process only takes a few moments—just until the spices start smelling fragrant.
For this soup I'm using spicy harissa paste, along with some cumin and coriander seed to emphasize that North African flavor profile.
Step 5: Add Your Liquid
Your choice of liquid can have a big impact on the finished dish.
- Chicken stock is an easy fallback and always a good choice. It has a neutral, mild flavor that adds meatiness and savoriness to a dish without overwhelming any flavors. Likewise vegetable stock can bring similar complexity, though buyer beware: unlike store-bought chicken broth, most store-bought vegetable broths are vile. You're better off making your own.
- Vegetable juice is what you want if you value intensity of vegetable flavor over balance. Carrots cooked and pureed in carrot juice will taste insanely carroty. You can buy many vegetable juices at the supermarket these days, or juice your own with a home juicer. Mixing and matching a main ingredient with a different vegetable juice (like in my recipe for Roasted Squash and Raw Carrot Soup) can lead to great end results.
- Dairy such as milk or buttermilk is a good way to get yourself a heartier, creamier dish, though dairy fat does have the tendency to dull bright flavors. This is not necessarily a bad thing: dairy is the perfect foil for the intense flavor of broccoli in a creamy broccoli soup, or tomatoes in a cream of tomato soup, for instance.
- Water is a perfectly fine choice if the other options aren't available.
Whatever liquid you choose, don't use too much. Use just enough to cover your ingredients by an inch or so. You can always thin a thick soup out after blending, but reducing a puréed soup that's too thin is a much more difficult thing to do (if you don't want to risk burning it to the bottom of the pot).
After adding your liquid and main ingredient bring it to a simmer, and let it cook until the vegetables are just cooked through; you want them to be just tender enough to pierce with a knife with no resistance. For things like carrots, parsnips, and other root vegetables, you have a bit of leeway here. Overcooking won't be the end of the world. But for bright green vegetables like broccoli, asparagus, peas, string beans, or leafy greens, you want to make sure to stop cooking them before they start turning a drab green color—if a brightly colored soup is something you care about, that is.
For this soup I'm using a homemade vegetable stock (though chicken stock would be fine).
Step 6: Purée and Emulsify
Here's the fun part: puréeing. The smoothness of your final soup will depend on the tool you use.
- A blender will give you the absolute smoothest results, due to its high speed and vortex action. When blending hot liquids, always hold the lid down with a kitchen towel, start the blender on low, and slowly bring it up to high speed. Unless you enjoy wearing hot soup.
- An immersion blender can give you decently smooth results, depending on the power of your blender. It's by far the most convenient way to make soup, and it's a good choice if you're fine with a rustic, kind of chunky texture.
- A food processor should be your last choice. Because of their wide base and relatively low spinning rate, food processors do more chopping than puréeing.
Whatever method you choose to purée, I like to emulsify my soup with some fat during this stage—either butter or olive oil. This adds a rich texture to the soup.
Some recipes (including many of mine) will tell you to slowly drizzle in fat or add butter a knob at a time while the blender is running, which is a surefire way to get your fat to emulsify properly, but here's a secret: so long as you don't have the world's worst blender (and somebody out there does!), there's no real need to drizzle in the fat slowly. The vortex action of a blender is plenty powerful enough to emulsify the fat even if you just dump it all in at once.
If the ultimate in smoothness is your goal, finish off your puréed soup by using the bottom of a ladle to press it through a chinois or an ultra fine mesh strainer. The end results should be smoother than John Travolta strutting with a double decker pizza slice.*
*NB: there is one exception to the general rules here: potatoes. Because of their high starch content, potatoes should never be puréed in a blender, unless thick, gluey soup is what you're after. For a potato soup, your best bet to smoothness is to cook the potatoes in liquid, then drain and press them through a ricer, food mill, or tamis, whisking the pressed potato back into the soup to thicken it.
For this soup I'm using a high-speed blender and straining the soup through a chinois.
Step 7: Finish with Acid and Season
Seasoning is the final step just before plating and serving in any recipe. You can season as you go, but you never know if your soup has the right level of salt until you taste it in its final form. Now is the time to do that.
Equally important to bring out the best flavor in a recipe is acid. Because acidic ingredients quickly dull in flavor when cooked, it's best to add fresh acid right at the end, just before serving. For most vegetable-based dishes, lemon juice or lime juice is a great option, as their aroma complements vegetal flavors. Other good options would be a dash of cider vinegar, wine vinegar, or my favorite, sherry vinegar. The latter goes particularly well with soups made with plenty of extra-virgin olive oil.
For this soup I'm using fresh lemon juice.
Step 8: Garnish and Serve
Your soup is essentially done at this stage, but a little garnish never hurt anybody. Think of it as a necktie for your bowl.
At No. 9 Park, our chanterelle soup was garnished with a salad of haricots verts (that's fancy French talk for "green beans"), lobster meat, shallots, and toasted almonds. You don't need to get that fancy. When I'm making a simple soup for my wife and myself, it'll more often than not be a scattering of fresh chopped herbs and a drizzle of olive oil.
Here are some other options:
- Flavorful oils, like walnut, pistachio, squash seed, or argan.
- Chopped fresh herbs or tender alliums like parsley, tarragon, chives, or sliced scallions.
- Sautéed vegetables like mushrooms, leeks, or garlic.
- Nuts toasted in olive oil or butter, like almonds, hazelnuts, or pine nuts.
- Simple gremolata-style mixtures, like a blend of parsley, lemon zest, and grated garlic.
- Thinly sliced chilies.
- A drizzle of browned butter.
- Dairy products like sour cream, crème fraîche, or heavy cream; plain or flavored with spices or pastes. Using a hint of the same spice you used earlier in step 4 can be a good way to boost flavor.
I think of the garnish as a final step to layer flavor and/or texture into the bowl.
For this recipe I'm toasting pine nuts in olive oil, then combining them with chopped parsley and lemon zest.
Step 9: Rinse and Repeat
Once you've got these eight basic steps down, you've got what it takes to start creating any number of creamy soups, combining any flavors you like. I'm not promising that every single combination of vegetables and aromatics will work out for you, but use this guide as a blueprint and you're well on your way to building the soup of your dreams. You all dream about soup, right?