I went to a state school and at that time the school dinners for schools were cooked in some central establishment and delivered in dustbins to the school. Seemed bizarre then, eating food that came out of dustbins, and it still does. Those were the days. The food was generally unappetizing but one day was exceptionally bad. They had excelled themselves. The mashed potatoes, served in a metal scoop from the appropriate dustbin, tasted of soap. Powerful soap. Unwonderful soap. Yucky soap. None of us kids would eat it and the teacher in charge thought this was a bad thing. He forced us all to eat several forkfuls which were accompanied by retching noises, some of them real, some of them fake. Well, we were children. Eventually he decided to try it for himself. He cautiously began to eat a small portion, then spat it out, and agreed the mashed potato was inedible. This to a group of children who had effectively force-fed soap! We were magnanimously allowed to leave the rest of the potato.
I suspect someone somewhere in the central kitchens had been cleaning out the bin and carelessly dropped the soap in. The designated bin filler then simply dumped the mashed potatoes on top.
Any other tales of nasty inedibles or barely edibles?