When the 18th Amendment to the US Constitution was passed in 1919, prohibition banned the sale of alcohol but also made homebrewing illegal.  When prohibition was lifted in 1933 with the passing of the 21st Amendment, there was no language included in regard to homebrewing.  In 1978 President Carter signed H.R. 1337 which created an exemption from taxation for beer brewed at home for personal use. 

With the federal law being so vague, most states have written their own laws, however New York has has no legislation regarding brewing at home.  New York State statute, Chapter 3-B, Article 8, § 100 states that “No person shall manufacture for sale or sell at wholesale or retail any alcoholic beverage  within the state without obtaining the appropriate license therefore required by chapter”.