Beer was the one drink that had been sterilized and was safe to drink. Prior to hops, the stronger (more alcoholic) beer was, the longer it kept. The addition of hops is a preservative, thus allowing beer to be weaker and still keep longer. Hops allowed you to produce more beer from the same amount of malt. Reynold Scot, in A Perfite Platforme for a Hoppe Garden, states"whereas you cannot make above 8-9 gallons of a very indifferent ale from a bushel of malt, you may draw 18-20 gallons of very good beer." Hops also aid in clarification as well as head retention. More from "Hops: The Bitter Herb"