I've worked in dairy & electronic factories over the years and both had contracts to produce product for different companies using basically the same materials...! Why incur the huge cost of building a factory when there are many already set up to run multiple lines of different product down the same production line. A vat can hold any fluid milk, water, soda, orange juice, etc, etc. These companies are very happy to get the most use out of their equipment and production lines...!
It's especially helpful for small up & coming companies that don't have enough sales to justify borrowing to make their own factories...
My first hand experience was on the milk line where I would take the gallon jugs and place them in cases. As I was stacking Borden milk jugs suddenly without interruption, jugs of T G Lee milk came down the same line...! It was coming from the same vat....