The invention relates to a method and a device for improving the biodegradability of an organic sludge. It comprises at least two treatment cycles each of a total duration of between around 8 s and around 20 s and each comprising a first step of producing a first hydrolysed sludge emulsion in a first, reduced zone, by injecting a gas into said reduced zone. a second step of abruptly expanding the emulsion in a second zone—the expansion zone—and a third step of recovering the emulsion via a third, restriction zone.