That squat cardboard box in the baker's aisle does more than banish last night's fish smell from your refrigerator. When combined with specific ingredients, baking soda creates a chemical reaction resulting in baked goods that are light and high rather than dense and flat. Because sugar cookies are known for their interplay of crisp and tender textures, you might panic if you don't have baking soda at hand.
The Science of Soda
Baking soda helps cookies and other baked goods rise. To activate this leavening effect, cooks must mix baking soda with an acidic ingredient such as buttermilk or vinegar. Baking powder contains baking soda as well a powdered acid to activate the baking soda. Along with its non-culinary uses, baking soda is useful when an acid is integral to the flavor. It also works well in combination with baking powder to counteract acidic ingredients, when too much acidity would toughen the final product.
Take a Powder
If your baking soda dilemma stems from having baking powder but not baking soda in your pantry, take heart. The traditional sugar-cookie recipe calls for only baking powder because there aren't acidic ingredients in sugar cookies, such as molasses or lemon juice, that would counteract the powder's leavening ability. Baking soda can encourage extra browning when added to baking powder, but this consideration isn't needed with white sugar cookies.
Skirting the Soda
If you have neither baking soda nor baking powder, or simply eschew the taste of any chemical leavens in your cookies, consider shortbread. These sweet cookies rely on the right combination of butter, sugar and flour to give them their characteristic crumbly but tender texture. A basic recipe calls for about 2 parts white flour to 1 part each butter and sugar. Flavorings such as vanilla or almond extract may be added. Shortbread generally is cut into rounds, rectangles or wedges once the dough is formed.
If you're a traditionalist, it's helpful to know of other leavening. Potassium carbonate, or potash, pinch hits for baking soda, especially in German honey cake or gingerbread. Use the same amount of potassium carbonate as you would baking soda. For baking powder or baking soda, you may be able to find ammonium carbonate, or baker's ammonia. Use about 3/4 the amount of baker's ammonia as you would baking soda, or the same amount of baking powder. Reserve this ingredient for cookies, whose flat shape helps dissipate the ammonia taste during baking.