Combine yeast and warm water, stirring to dissolve; let stand 5 minutes or until bubbly. Set aside.
Place flour in a large bowl; cut in shortening with a pastry blender until mixture resembles coarse meal. Dissolve soda in buttermilk; add to flour mixture, stirring with a fork. Stir in sugar and yeast mixture, mixing well. Cover tightly and refrigerate 8 hours or overnight.
Turn dough out onto a lightly floured surface, and knead 4 to 5 times.
Roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place biscuits on greased baking sheets. Cover and let rise 1 hour. Bake at 400° for 12 minutes or until lightly browned.