Apologies if this is off-topic.
Every year, I make about 25 litres of cider vinegar. I wash the apples in a bucket of tap water, press them, add a sachet of yeast and leave the fermenting vessel in the garage. The juice is very acidic so not very pleasant to drink. It does however make tasty vinegar.
I have several fermenting buckets in the garage each with a different vintage of vinegar. Floating in each is a jelly-like mother of vinegar. Today I discovered that the yeast in one of the vessels (18 month vintage) has gone a bit wonky. The mother is about an inch thick. It's mostly jelly-like but the very top has the texture of pig skin, is very tough, and smells like cheese. The vinegar has lost its acidic taste and also has a hint of cheese.
Can anyone tell me what might have happened? Why has the mother become so tough? Why does it smell like cheese? Is it safe to eat?