While in college, I worked at a burger place that had a soft-serve machine. The cleaning process was rigorous every night at closing. Milk products harbor bacteria like nobody’s business and the soft-serve machine was the first thing that heath inspectors checked out.
There is no way the bleach/disinfectant would be left in the machine over night and the machine reassembled—the odor would tip anyone off. As I remember, we reassembled the machine after disinfecting and thoroughly rinsing the night before so the morning shift could have time to get it cold and pour in the shake mix.
Cleaning the machine was a pain, but we got to take home the soft serve that hadn’t sold that day, so we had that going for us.
The tedious process you just described is one main reason it’s common for McDonald’s to say “No Ice Cream today, the machine is ‘broken’, sorry!”.
I’ve heard many former employees say this. Some kids come to work and they are ready to get busy, even get their clothes a little messy if need be. Others have figured out how to glide through the shift with ease, doing only what is required (depending on who the manager is that shift) and nothing more. Every shift knows who the hardest workers are, and if they can be talked into doing the grunt work.
This dirty deed here, sounds as though it was done deliberately. Perhaps there just isn’t enough evidence to blame somebody. I still would never eat there again, at least not till the staff changed.
Ice machines are another piece of equipment health inspectors zero in on. Much for the same reason.