How to make a subtitute ermilk for a cheese recipe?

I'm making some homemade cheese; just for starters I'm not sure what kind it is... but the recipe is something like boil milk and 10 percent ermilk in a pan then let it cool and pour into a container let it sit and thaw out then pour into another container than again if needed..... does this sound right? and can I used lemon juice to make the ermilk or will that be much too sour? The cheese will be for anything like pastas, snack crackers or salads.