Shortening is a manufactured fat product derived from vegetables and plants. At room temperature shortening is a soft solid similar to butter with a very neutral and bland flavor that lacks salt. In baked goods shortening yields a more moist texture and crumb than butter. With a higher melting point it allows baked goods to rise better than both butter and oil by providing the ideal lubricate for gluten strands.
Substitute Butter with Shortening
When substituting butter with shortening in baking one needs to consider the content of both products to achieve a consistent end product. Shortening is pure fat where as butter is approximately 20% water. If a baking recipe calls for 20 grams of unsalted butter and you want to add shortening you would need to add 16 grams of shortening and 4 grams of water.
If a recipe calls for salted butter then you may need to add extra salt. The content of salt from brand to brand of salted butter varies greatly but is around 3% of the weight. 112 grams of butter, or a stick, would contain 3.1g of salt, approximately 3/4 teaspoon. Each tablespoon of butter, 14 grams, contains 0.39 grams of butter, approximately a small pinch.
If you want to use shortening but get the butter flavor this is where margarine comes in. Margarine is essentially shortening made to taste similar to butter and substitute with butter, this includes similar water content and salt content.