Set pineapple juice out to warm up to room temperature. Grease three 8 or 9 inch round cake pans. In large bowl, combine 3 cup flour, mashed potato flakes, sugar, salt, ginger, vanilla and yeast. In medium saucepan, heat milk, water, and margarine until very warm, 120-130F. Add warm liquid, pineapple juice, and eggs to flour mixture. Blend mixture at low speed until moistened; beat four minutes at medium speed. By hand, stir in 3 cups flour to form stiff dough. On floured surface, knead in 1/2 to 1 cup flour until smooth and elastic, about 5 minutes. Place dough in greased bowl; cover loosely with plastic wrap and cloth towel. Let rise in warm place, 80-85 degree F, until doubled in size, about 1 to 1-1/2 hours. Punch down dough. Divide into three parts; form into round balls and place in prepared pans. Cover pans; let rise in warm place until doubled in size, about 1 hour. Heat oven to 375 degrees. Bake 25-35 minutes or until loaves sound hollow when slightly tapped. Remove from pans immediately.