The vine holds a special place in the cultural life of Germany. Customs and traditions of the grape abound. One of the pleasantest and least well-known of these customs occurs here in the wine country at harvest time -- the drinking of Federweisser, the season's new white wine.

Available a few days after the grapes are pressed, Federweisser, or Feather-white, is barely old enough to qualify as wine at all. Normally it is consumed in the very early stages of fermentation -- the product has not yet clarified and the grape-juice flavor and high sugar content still remain.

Federweisser is not plain grape juice, however. There are signs of the wine to come. The brew usually has an appealing tang and fizziness (due to the release of carbonic acid during fermentation). And the alcohol content is beginning to rise. Moreover, at this point, still-active fermentation yeasts form a white, cloud-like suspension in the beverage -- which explains the seemingly whimsical name.

While some vineyards do of course produce red wines in Germany, no red wine equivalent of Federweisser exists. This is because in white wine production grape skins and stalks are separated from the juice before initial fermentation (thus permitting drinking), but are not removed until afterward in the production of reds.

Federweisser sampling was originally just a procedure anxious vintners used to check quality of the recent harvest. But now it's a standard autumn pleasure, enjoyed much like fresh, unpasteurized apple cider is in the United States. Many wine producers sell their own Federweisser, and occasional small inns and restaurants offer it in late October, or early November, as well.

Traditionally, Federweisser is served in large, cold glasses, along with a rich, onion-bacon pie called Zwiebelkuchen (onion kuchen). This popular seasonal specialty is similar to a quiche, except that a yeast-based rather than pastry crust is featured. It is said the dish is laden with butter and cream intentionally, to help coat the stomach and protect the unwary imbiber from alcohol in the new wine.

Here are several Zwiebelkuchen recipes. The dish makes hearty but economical lunch or supper fare. If you're interested in following the german custom, a batch of hard or nearly-hard apple cider is a good substitute for the Federweisser wine. ZWIEBELKUCHEN SCHWARTZWALDER ART (10 or 11 servings) Crust: 1/2 cup milk 1/2 cup butter 1 packet active dry yeast 1/4 cup very warm water (approximately 115 degrees) 2 eggs, beaten 1/2 teaspoon salt 3 to 3 1/4 cups all-purpose flour Topping: 1 cup finely cubed smoked slab bacon, or country-style ham 2 to 3 large onions, peeled and diced 2 tablespoons butter 2 teaspoons caraway seeds (optional)* 1 cup light cream or half and half 2 eggs 1/2 teaspoon salt

In a medium saucepan, scald milk and remove from the heat. Add butter and set aside till it melts and milk has cooled to warm. Meanwhile, in a measuring cup sprinkle yeast over the warm water. Stir until particles dissolve and set aside.

Place scalded milk in a large bowl. Stir in beaten eggs and salt, then yeast. A cup at a time, beat flour into the liquid. Add only enough flour to produce a very soft and moist, but workable, dough. Knead dough in the bowl for 6 minutes. Grease dough top and place bowl in a warm spot.

When dough is double in bulk, 45 to 55 minutes, punch down, knead 1 minute and divide into two equal portions. Press each portion into the bottom of a greased, 9-inch, deep-dish pie plate; make the layers as even as possible. oPut the plates in a warm spot and let dough rise 20 to 25 minutes.

Meanwhile, in a large skillet, fry bacon cubes until cooked through. Remove bacon from skillet, and drain off and descard fat. Place butter and onions in the skillet. Cook onions till transparent. Sprinkle onions, then bacon over the two crusts. Add a teaspoon of caraway seeds to each crust, if desired.

Beat together cream, eggs and salt. Pour mixture slowly over the two crusts. Bake in a preheated 350 degree oven 20 to 25 minutes, or until tops are browned and crusts baked through. Serve warm. Kuchens can be frozen and reheated, or the recipe may be halved, if you like.

*Caraway is an important seasoning in German food, and many Zwiebelkuchen recipes (but not all) include it. If you don't care for the flavor of these seeds, just omit them from the recipe. EASY ONION KUCHEN (8 to 10 servings)

This recipe features an "Americanized" short-cut; the yeast crust is formed from a package of refrigerator rolls. If you prefer to make your own from scratch, prepare crust as directed in the preceding recipe, let rise and then substitute for the refrigerator rolls. 1 package (8 ounces) layered (butterflake) refrigerator rolls 3 strips bacon 3 medium onions, peeled and thinly sliced 1 tablespoon butter or margarine 3/4 cup sour cream 2 tablespoons flour 2 eggs, beaten 1 cup milk 3/4 teaspoon salt

Separate layers of the rolls and, overlapping slightly, place on the bottom of a greased, 8-by-12-inch ovenproof pan. (If homemade crust is used, press into pan bottom and set aside to rise 15 minutes.) In a 400 degree, preheated oven, bake the crust layer 8 minutes.

Meanwhile, fry bacon strips until lightly done and remove from skillet. Add onions and butter to the skillet and cook over medium heat, stirring, until onions are limp and golden. Spoon onions into the crust. Crumble bacon and sprinkle over the onions.

In a small bowl, stir together 1/4 cup of the sour cream and the flour. When mixture is smooth, gradually stir in remaining sour cream, eggs, milk and salt. Pour mixture evenly over the crust. Bake kuchen at 400 degrees 22 to 25 minutes, until top is puffy and golden; reduce heat slightly if top begins to brown too rapidly. Serve immediately.