https://www.lambic.info/Brasserie_Mort_Subite#Brewing_Process
"Lebeau ascertained that the problem was originating in the coolship which was too small and too deep, and that it could not handle the amount of wort being pumped into it. To combat this problem, he began to divide the batches in two and pump half into a steel tank which was filled with regional air. When analysis showed that the batches pumped into the tank picked up as much wild yeast to initiate fermentation, the coolship was eventually retired all together. This method, known as the "Lebeau Method," was a modified version of the
GKZ Method used at Belle Vue to help reduce infection and increase product consistency.[1]
As a result of Lebeau's discoveries, Mort Subite ceased using the
koelschip in the early 1990's. Instead, the wort is cooled using a plate cooler to 30°C to prevent infection. Next the beer is placed in a steel tank that was filled with air from the region, rather than sanitized air or CO₂, to introduce microorganisms from the region. Similar air is also placed in the pipes. Because this regional air is not sterile, the wild yeasts that are present begin fermentation. This allows Mort Subite to brew year round, rather than just in the traditional winter season.
[1]"
And Belle Vue as well:
https://www.lambic.info/Brasserie_Belle_Vue#Brewing_Process
"Belle Vue does not follow traditional
lambic brewing processes. Instead, Belle Vue uses a process called the DKZ method (DK - De Keersmaeker, Z - Zuun) for spontaneously fermenting its lambic. This process abandons the coolship and instead uses a two step process where the lambic is first cooled using a traditional heat exchanger and then non-sterile, compressed air is pushed into the tanks. This introduces the local microorganisms to the wort. Belle Vue also blends old lambic back into the tanks at this time to further ensure that the young wort is inoculated."