Semisweet chocolate chips are the default mix-in for most chocolate chip cookie recipes. Over the past several years, consumers have seen a huge increase in the variety of chocolate chips (and chocolate chunks) available at the grocery store as options for baking. One question I get asked frequently is whether it is ok to substitute one type of chocolate chips for another, and what difference it will make in the final recipe.
The short answer is that it is perfectly fine to substitute one type of chocolate chips for another in a recipe that calls for them. This is true for cookies, cakes, brownies and other recipes that call for mixing-in a quantity of chocolate chips. Most recipes call for semisweet chocolate by default, as those are still the most common type of chocolate chip, but some will make recommendations for milk or dark chocolate chips based on what the recipe author thinks tastes best in that recipe.
All chocolate is made up of cocoa solids – cocoa butter and cocoa powder – and typically includes sugar, an emulsifier and vanilla. Milk chocolate has milk solids added to it as well, while dark chocolate does not. Semisweet chocolate is not strictly defined (there is no exact amount of sugar to be called “semisweet”, though it generally means no more than 50% of the mass of the chocolate is sugar as opposed to “sweet” chocolates, where there is even more sugar) but it is essentially dark chocolate because it does not contain milk solids. Semisweet chocolates are not typically very sweet, but they are sweeter, not as intensely flavored and lack the bitter notes that some “ultra-dark” chocolates have. Semisweet chocolate gives a balanced flavor to most chocolate chip cookie recipes, adding just the right amount of sweetness and chocolate flavor. A darker chocolate, with more bitter cocoa notes than semisweet, will have a stronger presence in a cookie or cake and may overwhelm some of the subtle flavors in that recipe. Milk chocolate is typically much sweeter than either of these and can actually taste too sweet in a cookie or cake, as it does not add enough contrasting chocolate flavor.