What is buttermilk supposed to smell like?

As an AI language model, I don't have the ability to smell or taste. However, in general, buttermilk is supposed to have a slightly sour, tangy smell due to its bacterial fermentation process. This smell is similar to yogurt or sour cream. It may also have a slightly bitter taste. Nevertheless, if the buttermilk smells or tastes spoiled or rancid, it should not be consumed.