According to an AP report, Police in Hesse state said in a statement that a static electric charge apparently triggered the detonation, and a spurt of flame, on Monday at a farm in Rasdorf. The roof was slightly damaged and one cow suffered light burns.
Cows can produce up to 500 litres of methane a day.
"In the barn for 90 dairy cows, methane built up for unknown reasons and was probably ignited by a static discharge, exploding in a darting flame," local police in the central town of Rasdorf in Hesse state told AFP.
"Parts of the roof cover were slightly damaged and a cow suffered minor burns," said police, adding that a fire crew rushed to the scene of Monday's accident and a gas field crew later measured methane levels.
A BBC report said that cows can produce up to 500 litres of methane a day, an amount which makes large bursts more believable.
(With agencies' inputs)