Q+A; Heating and Depleting
By C. CLAIBORNE RAY
Published: November 4, 2008
Q.When scum is skimmed off homemade soup, what nutrients are lost?
A. Soup scum consists primarily of coagulated protein combined with fat, said Christina Stark, a nutritionist at Cornell University.
''As you begin making soup, heat causes a small proportion of the dissolved meat or vegetable proteins to coagulate, or clump up, in new ways,'' she said. ''As the soup continues to heat, oils in the water also go to the surface and combine with the proteins, creating the foam or froth you see.''
''We get plenty of those nutrients in our diets,'' she said, ''so skimming the scum away won't lead to any significant nutrient losses.'' She pointed out that if taking off the scum entices you to eat a larger serving of clearer and more appetizing vegetable soup, ''then you could end up consuming more nutrients than if you left the scum.''
A more important nutrient loss can occur in the vegetables before and during preparation, Ms. Stark said. Vitamins and minerals vary in their sensitivity to environmental factors. Vitamin C is water-soluble and is sensitive to oxygen, light and heat, but stable in acid conditions. Folic acid, another water-soluble vitamin, is unstable in acid and light, but stable when exposed to oxygen or heat. Minerals and fiber are generally stable in all these conditions.
''So for example, if the broccoli was shipped across country and then sat for days on the store shelf or at home before being used, there may be significant losses of vitamin C before it ever gets into the soup,'' she said.
But the good news with soup is that ''you generally consume any water-soluble vitamins that have leached into the broth,'' Ms. Stark said.
DRAWING (DRAWING BY VICTORIA ROBERTS)