When Ponce de Leon was scouting about Florida looking for the fountain of youth, he should have been staying home reading the Bible. In the Old Testament, it says that the prophet Abraham lived to be 175 and even managed to reproduce at 100. Ancient rumors attribute his longevity to recipe for yogurt provided by some health-minded angel. Old Abraham kept his bags of beneficial bacteria-soured milk stored in goat skins and lived happily for almost ever after.

The notion that bacteria, even an ominous sounding growth like lactobacillus bulgaricus, can be good for you is impressive.It was interesting enough to get Ilya Metchinikoff the Nobel Prize in 1908 for discovering that yogurt produced such a friendly bacteria.

Metchinikoff discoved yogurt worked like an antibiotic -- the good yogurt bacteria breaks down bad bacteria in the large intestine. It was later proved to be beneficial to people taking sulpha drugs and pencillin, which destroy B-complex vitamins and nice intestinal flora.

Many other theories on the miracles of yogurt have been offered -- it prohibits the build-up of cholesterol and increase fertility (both unconfirmed). Whatever the beneficial propeties may be, nothing good will come if the culture is dead or killed off as it is many commerical brands. Check the ingredients on the side of the carton and buy one that contains live yogurt cultures.

It is cheaper to make yogurt at home, but you can run into some difficulties:

If the yogurt starter is too old or the milk not fresh, you will end up with milk. The only thing to do is start over with new milk and fresh starter.

If you make the yogurt in containers that are not clean, the unclean bacteria will interrupt the yogurt bacteria and you end up with milk. Start afresh.

If you add too much starter to the milk, you get a sour watery yogurt because the culture has no room to breathe.

If the temperature of the milk is too low during incubation, the culture can't grow. This one you can save. Just warm it up slightly and incubate again.

Yogurt can be substituted in many recipes that call for sour cream and is a refreshing summer substitute for heavy sauces and dips. Below are some yogurt recipes that are fast and perfect for overheated cooks.

YOGURT DILL DIP 8 ounces yogurt 8 ounces cream cheese 3 tablespoons fresh dill or 1 tablespoon dried dill weed Raw fresh vegetables (broccoli, green beans, peas, cucumber, carrots)

Mix the yogurt, cream cheese and dill until smooth. Slice vegetables into sticks and serve with dip.

YOGURT SALAD (5 to 6 servings) 2 tomatoes, chopped 2 scallions, chopped 1 cucumber, peeled and sliced 1 apple, chopped Raisins (optional) 1/4 cup coarsly chopped walnuts 8 ounces yogurt Salt and pepper to taste

Sprinkle sliced cucumbers with salt and let drain for 15 minutes in a colander. Rinse and mix with remaining ingredients. Serve chilled in lettuce cups.

COLD CUCUMBER AND WATERCRESS SOUP (4 to 6 servings) 2 tablespoons butter 2 scallions, chopped 2cups diced (buy not peeled) cucumber 1 new or red potato, diced 1 cup lightly packed watercress leaves 2 cups chicken broth 1 bay leaf 1/2 teaspoon salt Pepper to taste Pinch of dried dill weed 2 cups plain yogurt

In a saucepan, saute the scallions until soft. Add remaining ingredients except yogurt and bring the mixture to a boil. Lower heat and simmer about 10 minutes or until potato is tender.

Puree mixture in a blender and cool. Add yogurt and refrigerate for 1 hour.

SPINACH PUDDING (4 servings) 2 pounds fresh spinach, or two 10-ounce packages forzen chopped spinach 2 tablespoons butter 1 tablespoon minced shallots or scallions 2 tablespoons flour 3/4 cup yogurt Salt and pepper to taste 1/8 to 1/4 teaspoon nutmeg Pinch of cayenne pepper (optional) 2 eggs, lightly beaten

Preheat oven to 375 degrees. Cook spinach according to package directions and drain thoroughly. If using fresh spinach, chop coarsely.

In a heavy saucepan, melt the butter and add the minced shallots or scallions. Cook over medium heat until soft, but not brown. Add flour and stir until blended. Cook 1 to 2 minutes and add yogurt. Cook, stirring, until the sauce is thick and starting to bubble. Season with salt, pepper, nutmeg and cayenne. Mix in spinach and remove pan from heat. Cool then add beaten eggs, stirring well.

Butter a 4-cup baking dish and pour in spinach mixture. Set baking dish in pan containing about 1/2 inch hot water and place on rack in lower third of oven. Bake about 35 minutes until puff and golden brown.

Adapted from "The Yogurt Gourmet," by Anne Lanigan

SEAFOOD NEWBURG (8 servings) 1/2 cup butter 1/2 pound fresh mushrooms, sliced 1/4 cup flour 1 teaspoon salt Dash white pepper 1/4 teaspoon paprika 2 cups milk 1 cup yogurt at room temperature 2 egg yolks 1/2 teaspoon Worcestershire sauce 1 tablespoon dry sherry 1 pound shelled shrimp, cooked 6 1/2 ounces fresh or canned crab, drained and flaked 1 pound fresh scallops, uncooked

Preheat oven to 325 degrees. Melt butter or margarine in a medium saucepan. Add mushrooms. Cook 5 minutes and remove from pan. Stir in flour, salt, white pepper and paprika. Cook over low heat until bubbly. Add milk. Cook about 5 minutes, stirring constantly until thickened. Simmer 10 minutes. In a small bowl, stir yogurt until creamy. Blend in egg yolks. Blend small amount of sauce into yogurt-egg mixture. Gradually add yogurt-sauce mixture to remaining sauce. Cook 5 minutes and remove from heat. Add Worcestershire sauce, wine and sauteed mushrooms. Cut shrimp in half lengthwise. Place half the shrimp, half the crabmeat and half the scallops in an 11-by-7-inch baking pan. Cover with half the sauce. Layer with remaining shrimp, crabmeat and scallops. Top with remaining sauce. Bake about 30 minutes or until lightly browned. Adaoted from "Yogurt Cookery," by Sophie Kay CAPTION: Illustration, no caption, By Susan Davis for The Washington Post