Bringing alcohol (including homemade wine) to the U.S. for personal use (note the .gov address, this is as official as it gets)
Generally, one liter of alcohol per person may be entered into the U.S. duty-free by travelers who are 21 or older
It is not legal for travelers under the age of 21 to import alcohol - even as a gift.
Alcoholic beverages purchased in duty-free shops are subject to duty and federal excise tax when accompanying you into the United States.
NOTE: The above information is applicable to homemade wine and follows the same procedure as store bought wine. The bottles should be properly labeled.
However, As a visitor to the United States what are my exemptions on gifts for family and friends? claims:
This $100 gift exemption, or any part of it, can be claimed only once every six months. You may include 100 cigars within the gift exemption, but alcoholic beverages may not be included.
So I would definitely tell the customs official that I have this bottle of alcohol with me, since it's only 1L it'll be fine but be prepared to pay duties (or not pay duties if it falls under the "personal use" category). Never lie to customs and never offer any information not asked for.
Finally, the amount of duty How do I import alcohol for my personal use?
Duty on wine and beer is generally low, $1-2 per liter, while fortified wines and spirits are considerably higher.
Looking at Harmonized Tariff Schedule of the United States (2013) I can only say that indeed that around $1.4 is what I would expect in duties plus there is an excise tax which seems to be 13.50 for one gallon of 50% alcohol looks like $2.7 for 1L of 40% alcohol. So at the end, you are looking at