SOUPS and stews are standard fare in winter but for Chinese, soup is very important food therapy. Traditional Cantonese energy-reinforcing soup (bao tang) is especially popular because it tastes good and boosts health.

Traditional Chinese medicine experts say making healthy soup is more than putting all the ingredients in a pot and boiling. The most effective absorption of therapeutic ingredients depends on careful selection of ingredients, selection of the container, level of heat, duration of cooking and the time of the day to drink soup.

TCM nutritionists offer a few tips.

Ingredients

Animal foods like chicken, duck, pork, beef and fish are all yang ("warm" energy) foods and are common ingredients in Cantonese reinforcing soup. Animals should be killed within three to five hours, since they provide the best nutrition that is easy to absorb, according to chef Li Guosen from The Eton Hotel Shanghai who prepares reinforcing soup for guests every winter.

Quickly boiling meat or fish first helps get rid of blood and excessive fat and keeps the soup clear; it should be skimmed.

Yam, turnip, kelp and lotus roots are recommended because they provide fiber and vitamins that are not damaged by high heat.

TCM herbs like ginseng and gouqi (wolfberry fruit) are very important to add in cold weather. Aweto (cordyceps) and huangqi (astragalus root) are also commonly used for reinforcement. All these herbs activate blood circulation and improve kidney energy, while not adding an overpowering herbal taste.

Container, heat and water

Pottery pots are best for making reinforcing soup since the clay helps transfer heat evenly and slowly; it is very important for water and ingredients to permeate each other. The more it is cooked, the better the taste and aroma.

Boiling first, then simmering for one or one and a half hours is recommended, says nutritionist Wang Leijun. Overheating may destroy amino acid rather than improving nutrition and making it bio-available.

It takes less time to cook fish soup; when it turns white, it's done; that's usually around 40 minutes. Greens should be added when the soup is almost done to preserve vitamins and minerals.

The proportion of 1:2, ingredients to water, preserves proper density of nutrition and flavor. It's best to begin cooking ingredients together slowly, starting with cold water.

Sharp temperature change may solidify protein and keep the nutrition from melting into the soup. It's not a good idea to add cold water midway in the cooking process for the same reason.

Seasoning

Unsalted soup generally provides the best nutrition, but most people like some salt. Nutritionists suggest not adding salt until the soup is done, again to prevent solidifying protein and destroying some nutrition. Seasonings like sesame oil, pepper, ginger and green onions can all be used, as can one or two jujubes.

Serving

Drinking a bowl of soup before meals helps improve digestion and absorption, since it adds moisture to the digestive system and dilutes food. More important, eating a bowl of soup before meals gives a feeling of fullness and helps prevent overeating.