I'm a little late in writing my review; I tried this for Thanksgiving. I do believe the apple cider acted as a subtle flavor enhancer and improved the flavor of the gravy.
This one is tricky to review--it's hard to compare sips out of two different cups of HOT liquid. But, like slickchick and steve, I think I detected a more robust difference too! I thought, "Aw heck, apple cider vinegar is a cure-all tonic for everything," and added the tester cup and more cider vinegar back into the remaining gravy. We loved it and I think we're healthier now too!
It does add more flavor and body to the gravy. I tried it with pork roast gravy and it was delicious.
In an old 1800's cookbook there was mention of using vinegar in gravy but I had forgotten about it.
Unfortunately, the cookbook and other antiques was burned in a fire in an outbuilding. I can't verify this use then. Thanks for posting.
Used your tip for the gravy on the turkey(77861) I just made. Really think it did add more flavor to the gravy. This is the 1st gravy I have ever made that has a really good turkey taste. Thanks for the easy tip :)