"This is how it works: each morning, from about ten o'clock until lunch, at one, the taster receives in his office those farmers and distillers who have come to offer him samples of their cognac. The taster has eaten only a very small breakfast hours before. His stomach is practically empty...The taster never fills the glass with cognac, for that way the bouquet is lost. Instead, he pours in the cognac until the glass is one-third or at most half filled. Then he turns the glass so that the cognac is twirled in the glass and it's vapors mix even more with the air of the glass..."
A fascinating read.
This site has more food and wine articles.
A Cognac Glass from Amazon...