What does IBU measure in beer?

IBU, or International Bitterness Units, specifically measures the bitterness in beer that comes from dissolved alpha acids, which are primarily derived from hops. When hops are added to the brewing process, they contribute bitterness through these alpha acids during the boil. The higher the IBU value, the more bitterness is present in the beer. This measurement allows brewers and consumers to assess the balance of flavors in a beer, as it directly influences the perception of sweetness, malt character, and overall drinkability.

The other options relate to different aspects of beer production. The amount of alcohol in beer is measured by alcohol by volume (ABV), while sweetness is typically measured in terms of residual sugars, not directly related to IBU. Carbonation levels in beer are measured differently, often quantified in volumes of CO2 or through perceived carbonation but do not relate to IBU measurements. Thus, the focus of IBU is specifically on bitterness, making the correct answer the measurement of bitterness from dissolved alpha acids.