LACTOSE

Lactose

• Milk stout (also called sweet stout or cream stout) is a stout containing lactose, a sugar derived from milk.
• Because lactose is unfermentable by beer yeast, it adds sweetness, body to the finished beer.
• The lactose used in the brewing process is not all converted to alcohol. Therefore, some trace amounts are left to provide a fuller body and mouthfeel in the final product. 
• The Lactose that is left in the beer imparts sweet flavors desirable in the styles that it's typically used in – stouts, sours, and some IPAs.