I am confused about buttermilk in cake recipes. The recipes don't specify which type of buttermilk - whole fat or low- or nonfat. Will using low-fat or nonfat buttermilk change the taste?
The recipes probably don't specify a fat level because most buttermilk is low-fat or nonfat.
Originally, buttermilk was what was left after butter had been churned from full-fat milk. Since the fat became butter, the milk left behind was low-fat or nonfat.
These days, most buttermilk is cultured, similar to yogurt. That means it's made by adding a bacteria, Streptococcus lactis, to nonfat or low-fat milk.
The fat level, however, isn't what's important about baking with buttermilk. In addition to its tangy flavor, buttermilk is high in acidity, so it reacts with baking soda, helping to leaven baked goods. It also can be a natural tenderizer, which is why so many fried chicken recipes start by soaking chicken in buttermilk.
If you don't have buttermilk, you can make it by adding an acid - usually vinegar or lemon juice - to milk. Or you can buy powdered buttermilk, which keeps a long time in the refrigerator. Follow the instructions on the label.