Oud bruin

Oud Bruin
Liefman's oud bruin
Country of origin	Belgium
Yeast type	Top-fermenting
Alcohol by volume	4 - 8%
Color (SRM)	15 - 22
Bitterness (IBU)	15 - 25
Original Gravity	1.043 - 1.077
Final Gravity	1.012 - 1.016
Malt percentage	90% - 100%

Oud Bruin (Old Brown), also known as Flanders Brown, is a style of beer originating from the Flemish region of Belgium. The Dutch name refers to the long aging process, up to a year. It undergoes a secondary fermentation, which takes several weeks to a month, and is followed by bottle aging for several more months. The extended aging allows residual yeast and bacteria to develop a sour flavor characteristic for this style. Usually, cultured yeast and bacterias are used, as stainless does not harbor wild organisms as wood does.

These beers were kept as so called provision beers, to be stored and allow the flavor to develop. Liefmans Brewery has been brewing the style since the 17th century. Historical examples tended to be more sour than modern commercial products.

This style of beer is medium bodied, reddish-brown, and has a gentle malty flavor and no hop bitterness. Commercial versions may mix aged beer with younger, sweeter beer to temper the acidity and allow for further fermentation.