When you're baking cakes, pies or cookies, you can substitute shortening for butter, or the other way around. But you can't substitute them equally.
In other words, a tablespoon of butter is not equivalent to a tablespoon of shortening.
Why? Because while shortening is 100 percent fat, butter is only about 80 percent fat. About 15 percent of butter is water, and the rest is milk solids.
So, when you have a recipe that calls for butter, you can substitute shortening, but you have to make some adjustments.
And there is some very basic kitchen math involved.
Substituting Shortening for Butter
For instance, let's say you have a cookie recipe that calls for two sticks of butter (or 226 grams), but you want to use shortening instead. There are two steps:
- Multiply the weight of the butter by 0.8, which gives you 181 grams of shortening.
- Then multiply the weight of the butter by 0.15, which gives you 34 grams (approximately 2 tablespoons) of milk or water that you need to add, to make up for the water in the butter.
You could leave out the extra liquid, and your cookies will spread less and be chewier.
Substituting Butter for Shortening
You can make the same conversion going the other way. Let's say you have a cake recipe that uses ½ cup of shortening (52 grams), but you want to use butter instead. There are again two steps:
- Multiply the weight of the shortening by 1.25, which gives you 65 grams, which is how much butter you will need to use.
- Then multiply the weight of the butter by 0.15, which gives you about 10 grams of liquid, or about 2 teaspoons, that you'll need to subtract from the recipe.
It's a minor adjustment, but with baking, your ingredients need to be measured with reasonable precision if you want things to turn out the way the recipe is supposed to.
And to be clear, it is worth pointing out that if you do substitute shortening for butter (or vice-versa) without making these adjustments, it does not necessarily mean that the recipe is going to turn out badly. Indeed, a tablespoon or two of liquid one way or another, in a recipe that makes 60 cookies, is not enough to make the difference between good cookies and bad ones.
All it means is that, as noted earlier, the texture of the cookies might be a tiny bit different—chewier or crispier, depending on which way you're substituting. If you've made the recipe before, you might want it to come out as close as possible to the way it came out the last time.
Finally, note that we're talking in terms of grams here, which is because weights (not volume measurements like cups) are a most accurate way to measure ingredients in baking. A digital scale that can be set to grams is a really handy if you do a lot of baking. See Measuring Ingredients in Baking for more about that.