Replacing milk with soy milk is one of the easier substitutions in cooking and baking. Substitute equal amounts of milk and soy milk: If a soup recipe calls for 2 cups of milk, replace it with 2 cups of soy milk. The same can be said for rice milk and almond milk. But when making this substitution, there are a few things you should keep in mind. Besides the flavor, when to add the soy milk and which ingredients can alter the consistency of the soy milk top the list.