the appetizer:

The Science of Good Food by Andrew Schloss and David Joachim explains the mysteries of food and cooking. Check out topics like Caviar; Extracts; and Sweet Potatoes; plus recipes, including Acorn Squash Filled with Pumpkin Seed Risotto and Roasted Root Vegetables.

Cookbook Profile

Roasted Root Vegetables

Makes 6 servings


As root vegetables roast their starch breaks down into sugar, and the sugar caramelizes. At the same time, aromatic components in the vegetables become concentrated resulting in richer sweeter flavors than can't be attained by boiling or steaming the same vegetables. Serve as a side dish or in any recipe calling for roasted vegetables.

Preheat the oven to 425°F (220°C). On a rimmed baking sheet, toss together onions, sweet potato, carrots, celery root, and turnip. Add oil and toss to coat. Season liberally with salt and pepper. Spread out in a single layer. Roast in preheated oven for 30 minutes. Add garlic, and continue roasting, until the edges of most of the vegetables have browned and they are uniformly tender but not mushy, for 5 minutes more.

Serve immediately or cool and refrigerate in a tightly closed container for up to 1 week.

What It Is

Roots anchor plants to the ground, absorbing moisture and nutrients from the soil and conducting them into above ground parts of the plant. Most plant roots are spindly, fibrous, and inedible, but some are engorged with storage cells that are loaded with carbohydrates and other nutrients, and these are the ones that have been cultivated as vegetables. Root storage is intended to help nourish the plant during times of deprivation, but it also provides the same nutrition (and some pleasurable flavors) to anyone who is fortunate enough to dig up a root vegetable and eat it.

What It Does

The storage tissues in roots developed in a variety of ways. Some, like potatoes, cassava, and taro, store their energy in the form of starch tissue. Others, such as beets, carrots, and parsnips, store energy as sugar. Technically, beets and celery root are swollen stem bases, but because they store energy, which makes them nutritious and sweet, they taste like roots and are cooked like other roots, and therefore are thought of as root vegetables. Compared with other types of vegetables (stems, leaves, fruits, etc.), root vegetables are sturdy and relatively low in moisture, which allows them to be stored for many months without decomposing. Some anthropologists think that the discovery of starchy roots in the African savannah about 2 million years ago may have fueled human evolution. Raw starch is not easily digested, so starchy root vegetables must be cooked to be edible. Early people who learned to forage for and cook roots would have had a nutritional and evolutionary advantage over those who depended on more perishable food. Although starchy roots have to be cooked, those that store their energy as sugar can be eaten raw, provided that they are harvested young. As sweet-tasting roots like carrots and beets, which can be as much as 5% sugar by weight, mature they get bigger, their cell walls thicken, and the vascular tissue that runs through the root becomes woody. Eventually the fibers become too tough for humans to break them down enough to get much sweetness out of the vegetable, so old carrots and beets have to be cooked to release their sugars.

How It Works

Root vegetables that store energy as starch are drier and denser than those that contain more sugar. When starchy root vegetables are cooked, the starch swells, causing the starch granules to separate from one another, producing a dry, mealy texture. The cells of sweet roots, on the other hand, soften and cohere to one another as they cook. The moisture held within the cells is released, and their texture becomes soft and moist.

In general, root vegetables should be stored in the dark. Light, especially sunlight, can cause off-flavors and the development of toxic defensive chemicals. White roots such as parsnips, white carrots, and turnips can generate alcohol compounds that give the vegetable a turpentine-like solvent aroma. Potatoes contain small amounts of the toxic bitter-tasting alkaloids solanine and chaconine, which accumulate when the vegetable is exposed to light. Because light also activates chlorophyll, the growth of these alkaloids is typically accompanied by a green tinge to the surface of the vegetable. Most of the problematic compounds concentrate near the surface of the root and can largely be eliminated by deeply peeling the skin. Some roots, particularly beets and potatoes, contain an earthy (some might say dirty) flavor component, geosmin, which was once thought to come from microbes in soil but now is thought to generate in the vegetable itself. It is particularly pronounced in large mature vegetables.


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This page created January 2009