WFMC, spot on.

Yes, to sour milk, any acid of a neutral color and flavor will do just fine.

Like wssmom, I use yogurt thinned with milk. I've also added lemon juice to milk (instead of vinegar) and it has turned out fine.

I use yogurt in pancakes. I could use kifer for a similar flavor but I like the viscosity of yogurt because it can be thinned out with amber beer. It would probably make marvelous muffins too.

Oh yeah, I'll bet that's great.

What boulangere says!! Sometimes I use greek yogurt thinned with some milk and that works out fine.

Why? Do you not have any? If so, you can easily sour milk by either whisking in a teaspoon or so of white or cider vinegar (DON'T use balsamic - not a pretty story) and let it sit for 5 minutes. Alternatively, you can divide the amount of milk to 75% milk and 25% sour cream and whisk them together. If you want to avoid buttermilk entirely, use whole milk, but remove the baking soda from the list of ingredients unless you're making, say banana bread, or something containing an additional acid. It's present whenever an acid is,.