Acidic milk in red carton. Butter milk. What does this packaging contain and how do you convert milk into butter milk? It’s almost impossible to find an old-fashioned churn in most milk and butter plants. But does it actually matter how you sour milk? To find out, Dutch TV program ‘De Keuringsdienst van Waren’ visits both farmer and dairy plant. Vecozuivel’s plant, as a matter of fact.