How to Use Old Milk - as part of the expert series by GeoBeats. Have you ever opened a container of milk and it kind of has that funny smell to it? Well, milk does get sour sometimes. That is the lactobacillus bacteria in our milk, which is eating the lactose or milk sugar and turning it in to lactic acid, making it taste a little bit sour. You do not have to throw out that milk out right away, even though you might not want to drink it anymore. There are some good uses for it. First of all, you can use it in almost any recipe that calls for butter milk. So if you are making pancakes or muffins that require butter milk, use that sour milk instead. But here is a creative idea that you might not have thought of. You could use that sour milk to make your own cheese. I like to use it to make an Indian cheese called 'paneer'. Which is often used in a dish called 'palak paneer' or paneer with spinach. The way you would do it, is to take our half gallon of milk, pour it in to a large sauce pan and bring it to a boil on a stove top. Once it reaches a boil we are going to turn it down to low heat and add three tablespoons of vinegar. I am going to go ahead and pour the vinegar in advance so it is ready to go in to the boiling milk. We are going to use white distilled vinegar. Then, once we have added the vinegar we remove the milk pot from the heat, we are going to pour it through a cheese cloth-lined strainer, bring out the edges of our cheese cloth, squeeze out the liquid and the remaining curd is our cheese. We will form it to the shape that we want and then we will refrigerate it, we will cut it and use it whenever we are ready. And that is how we make cheese out of sour milk.