Does anyone have any ideas of how to use up acid whey? It is slightly salty, but not terribly so.

In addition to using it in pancake or waffle batter (my most common use), I also use it in cobbler toppings and substitute about half of what's call for in other baked good recipes calling for buttermilk. It's also wonderful as a component (I use half whey, half 2% milk) in the baked oatmeal I make for my husband every week.

Here's an article you might find helpful:

https://food52.com/blog/14715-12-ways-to-use-up-whey

Keep in mind that an acidic whey may affect yeast, so when that's a concern, I add a touch of baking soda to the dry ingredients, to counteract that.

Here's a bread recipe featuring whey:

https://food52.com/recipes/10040-ricotta-whey-and-barley-bread

Hope this helps. ;o)

I use up the whey from cheesemaking in waffle or pancake batter.