Soy milk provides an effective substitute for cow's milk for people with lactose intolerance. The milk, produced from soy beans, is also suitable for anyone following a vegan diet, meaning one that doesn't include any animal products. Generally speaking, soy milk can be substituted for cow's milk in baking without impacting the quality of the batter.
Pour soy milk -- about 80 percent of the milk that the recipe calls for -- into a separate mixing bowl. For most baking recipes, it's best to use unsweetened soy milk as your recipe most likely calls for sugar as an ingredient. Use vanilla flavored soy milk if your recipe calls for vanilla extract.
Add one teaspoon of apple cider vinegar per cup of soy milk to the bowl and whisk. Allow the mixture to rest for 15 minutes until you notice a curdling effect. This technique breaks down the proteins and flavors in the soy milk, making it perform better as a substitute for cow's milk in baking.
Mix the soy milk and apple cider vinegar mixture into your recipe. Follow the rest of your recipe's instructions as normal.