I used 1 tsp of lemon and it didn't curdle, but I used it as was... I guess I'll see how it goes. If not too good, I'll use a Tbsp next time. Thanks for all the help.

There is potential for off-flavors from vinegar if you use too much, but I've found that in bread, vinegar can work even better. It depends on how much you're relying on the acid/baking soda or powder reaction to lift your bread. In a yeasted bread, I'm more likely to use lemon juice. In a quick bread, I'm more likely to use vinegar because I get a loftier height to my loaf. Sometimes, if I'm using very dense and heavy flours, I even use 1 tsp of each (lemon juice and cider vinegar).

Per Cooks Illustrated you add 1 Tbsp of lemon juice, white vinegar, or cream of tartar to 1 cup milk, and let the milk stand for 10 minutes. They say lemon juice is best, due to potential off-flavors from the vinegar and cream of tartar.

Awesome! Thanks, off to bake now!

Use about 1 tsp lemon juice or apple cider vinegar or white vinegar to 1 cup regular milk. Stir it in and you'll see it actually thicken and sort of curdle. The same principle works for soymilk.