Ale was a favorite drink in Medieval Europe, second only to wine, which was commoner in the warmer regions and among the richer folks.. Barley was most frequently used in the making of ale, with oats called into service when barley was not available or was too expensive. Strength of the brew would vary, depending on how much ale was made from the barley. A hundred liters of barley, plus the required malt, would yield anywhere from 17 to 33 gallons of ale. The more potent ale cost more. Ale was usually brewed by households, and done every week or so because ale would not keep. Those households that could afford to brew their own ale, sold or traded the surplus to those who could not. Commercial breweries in towns brewed large quantities for sale. Beer, which kept longer, was a German invention that became popular in England by the 15th century.