I know it’s supposed to be spring, but March winds are chilly and April showers are damp, and so a steaming bowl of soup is just what I want right about now. Soups run from clear broths to thick, hearty gumbos, but knowing a few important principles— like simmering instead of boiling and adding ingredients at the right time—can help you make any soup taste its best.
For a good soup, get a heavy pot
When I cooked in pots that had a stainless exterior with a layer of copper across the bottom and partially up the side, my food would always scorch right above the copper layer. This really impressed me with how important a good heat-spreading metal is. I like using a heavy-gauge pot with an enamel or stainless surface and a conductive core of aluminum, copper, or cast iron.
Watch the pot so it doesn’t boil
Boiling, especially vigorously, will cause the fat in the ingredients to emulsify with the liquid—just like shaking oil and vinegar in a vinaigrette—and will leave you with a cloudy, greasy stock or soup. Keeping the soup just below a simmer will prevent this emulsion, and most of the fat will then float to the top, where it’s easy to skim off.
Start with cold water for more flavor
Starting ingredients in a cold liquid more fully extracts their flavors. With slow heating, the starches in the vegetables swell more slowly and allow cells in the interior to break down and exude flavors more easily. (If you’ve ever tasted the celery or onions strained from a good stock, you found that they had practically no flavor: it all went into the stock.) This is especially important when you use just water or a canned stock as your soup base.
Another way to enhance the soup’s flavor base is to use old, soft vegetables—not rotten, mind you, just very “mature” ones. The insoluble pectic substances (the “glue” that holds the cells together) have converted to water-soluble pectins, so the cells fall apart easily and they readily contribute flavor to the liquid.
Layer ingredients to build complexity
Soup makers frequently add different ingredients at different times, depending on how long they want each to cook. But adding the same ingredient at different times can give a soup a delicious complexity. Louisiana chef Paul Prudhomme uses this technique, called layering, in his gumbo. He starts by adding onions, okra, bell peppers, and celery to a dark roux (fat and flour cooked until deep brown and very hot). These vegetables will be literally cooked to pieces when the gumbo is done, but they contribute deep flavor from their long cooking which started with intense heat. Midway through cooking time, he adds some of the same vegetables. These will cook until very soft. Near the end of the cooking time, he’ll again add more of the same vegetables (and perhaps a few others), which stay crisp and bright in the finished gumbo.
Layering doesn’t work with vegetables that develop unpleasant flavors and odors when cooked for long periods. Cabbage, cauliflower, Brussels sprouts, turnips, collard and mustard greens, kale, kohlrabi, and rutabaga produce double the amount of smelly hydrogen sulfide (rotten-egg smell) when cooking time is increased from 5-to 7-minutes. To keep members of this family mild and pleasant tasting, slice them thin or chop them for quick cooking and add them to the soup only 4-or 5-minutes before serving.
Brown ahead for a richer taste
Foods cooked in water will never get hotter than 212°F, so you can’t get the wonderful sweet compounds that form at higher temperatures (some of the compounds formed in long-cooked onions are even sweeter than sugar) or that form with browning. Browning meats or vegetables in a little fat in a hot skillet before adding them to the soup adds tremendous flavor.
Unlock Flavors with fat and alcohol
For a soup to be truly full-flavored and rich, you need to get all the flavors from every ingredient. Many flavor compounds dissolve in water, which is the base of most soups anyway. But other flavor compounds dissolve in fat, so a little fat (either added to the soup or from meat that’s in the soup) will unlock and carry flavors.
Alcohol is the “mystery ingredient” that can add the final flavor dimension to a soup. Whether in wine or spirits, alcohol dissolves both water and fat and also some compounds that aren’t dissolved by either water or fat. So a touch of sherry, Madeira, red, or white wine can add not only its own pleasing flavor to a soup, but it can also help unlock the flavor depths of the other ingredients.