Lemon zest is produced by grating the yellow side of a lemon's rind into thin strips with a grater or a zester. Zest may be called for to add citrus flavoring to such foods as cakes and salads. Because lemon extract contains a much stronger concentration of flavor, you only need half as much extract as you do zest to get the same citrus taste.
Determine how much lemon zest a recipe requires. For example, a lemon chiffon pie recipe typically calls for 1 tbsp. of fresh lemon zest.
Divide the amount of required lemon zest in half. Since 1 tbsp. equals 3 tsps., you would need 1 1/2 tsps. of lemon extract to substitute for the zest.
Add 1 1/2 tsps. of lemon extract to the recipe's other ingredients and follow the rest of the recipe's directions accordingly.