Here is an old article written about the positive effects of citric acid on cigars.
https://books.google.com/books?id=5XpBAQAAMAAJ&pg=RA1-PA27&lpg=RA1-PA27&dq=citric+acid+tobacco&source=bl&ots=OOXYDuaRFO&sig=iAY5-Kf9DbGYapxhYcBfHZTZjxE&hl=en&sa=X&ei=T0M3VJDNFaeIsQS764C4Bw&ved=0CEwQ6AEwBDgK#v=onepage&q=citric acid tobacco&f=false
https://books.google.com/books?id=5XpBAQAAMAAJ&pg=RA1-PA27&lpg=RA1-PA27&dq=citric+acid+tobacco&source=bl&ots=OOXYDuaRFO&sig=iAY5-Kf9DbGYapxhYcBfHZTZjxE&hl=en&sa=X&ei=T0M3VJDNFaeIsQS764C4Bw&ved=0CEwQ6AEwBDgK#v=onepage&q=citric acid tobacco&f=false