The Accidental Scientist: Science of Cooking
Candy Bread Eggs Pickles Meat Seasoning

Monthly Feature:
creamy soups without the cream

With today's focus on healthy eating, even soups have changed. Traditional cream soups derive their smooth texture from liberal amounts of milk or cream, thickened with flour or cornstarch. Now when we make soups that are creamy, chances are they contain no cream at all: They're likely thickened with purees made from starchy vegetables.

One of our favorites is butternut squash soup. It's similar to hearty soups made of pumpkin, potato, sweet potato or parsnip, all vegetables that are low in water and high in starch and fiber. As these vegetables cook, their starchy contents absorb liquid and swell, adding natural thickening power to the soup.

Making soups with such dense vegetables involves three basic steps, and each makes scientific sense.

Step One: Begin by sautéing aromatic vegetables, such as onions, leeks, or garlic, in a small amount of butter or olive oil. While these ingredients aren't noticed in the finished soup, they do add to its underlying character. As they sauté, their cell walls soften, releasing their inherent flavors and aromas. The fat or oil used in sautéing carries not only their own (now mellowed) flavors but also the flavor of any spices you choose to add. Consider grated ginger and sautéed shallots with carrot soup, coriander with broccoli, and nutmeg with parsnips. For some real zest, curry powder adds definite pizzazz to squash soup.

Step Two: Peel the vegetables (butternut squash peels easily) and cut the flesh into cubes. This step increases the surface area of the vegetable exposed to both heat and liquid, resulting in a shorter cooking time and a faster transference of flavors into the liquids. Now combine the sautéed onions or other aromatics with the cut vegetables and chicken or vegetable stock (or with squash try fresh apple juice). Use roughly 2 cups (500 ml) liquid to 4 cups (1 l) of chopped vegetables.

If you are featuring just one vegetable and it isn't particularly starchy—broccoli, for instance—add a small, thinly sliced potato or a 1/2 cup (125 ml) of rice. You won't notice either in the finished soup, but each swells during cooking and works well as a thickener. Simmer gently until the vegetables are tender.

Step Three: Puree the slightly cooled mixture in a blender. Or puree just half, leaving the remainder chunky. You might be surprised that a soup's "feel" as it rolls over your tongue strongly influences its appeal. Some people like smooth soups; others prefer a more substantial texture.

The process of pureeing releases both starch and fibers, which thicken the soup. With starchy vegetables, pureeing breaks down cell walls so their starchy contents spill through the broth. In vegetables such as broccoli, the cellulose that once held the stalk stiff is now transformed into minute fibers, which also add to the thickness of the soup.

Now that the vegetables have done their job, the final touches are up to you. A little freshly ground pepper? A touch of wine or sherry? A dollop of yogurt or crème fraîche?

January is such a good month to practice on soups. Try thickening with purees, improvising with ingredients and seasonings, and experimenting with various textures. Then we encourage you to add your wisdom, questions, and experiences to the Forum so we'll all benefit.

À la soupe!
Anne and Sue





© Exploratorium | Use Policy | Privacy Policy