They are *not* meant to be making you open and taste them -- it says so on the TSA website -- but it does happen. Yech.
"When carrying formula, breast milk, or juice through the checkpoint, they will be inspected, however, you or your infant or toddler will not be asked to test or taste breast milk, formula, or juice."
I've traveled with formula and they're one of the exceptions to the quantity rule, so you don't have to worry about how much is in the bottle. We brought 1 liter bottles last time!