Cultured butter is butter made from fermentation in cream, caused by bacteria creating lactic acid from the sugars in milk. Cultured butter is differentiated from non-cultured butter by the presence of bacteria during production. Non-cultured butter is made from fresh, sweet cream with no added bacteria or fermentation.
Cultured butter has a higher fat content than most butters commercially available in the U.S. It is shinier than whey or sweet cream butter. It is not intensely yellow, and has a more grassy and/or acidic taste than other kinds of butter. It is also softer, and easier to spread.
The key step in making cultured butter is adding one or a mix of the bacterial cultures Streptococcus diacetilactis or Streptococcus lactis to ferment the sugars in milk into lactic acid, according to the University of Georgia's food microbiology program. Lactic acid helps collect fat globules during churning, which means the butter is created much quicker in the churning process compared to other butters.
The lactic acid produced in cultured butter is directly related to the fermentation process. It adds the distinctive flavor to cultured butter and, by influencing the density of the butter's fat globules, makes the butter particularly spreadable.
Cultured butter is more widely consumed in Europe than in the United States. For that reason, it is more available commercially in Europe than in the U.S., although there are a small number of brands that consistently release cultured butter, homemade cultured butter is rare in the United States.