over- fermentation

I'm not a scientist but I do make all my own bread. Essentially over fermentation happens when the dough gets too hot and the yeast cells die off. The dough collapses. And really there's nothing you can do to rescue it. Unless you're happy to eat unleavened bread.

Under fermentation is when the dough is too cold and the yeast doesn't start working. That's easier to remedy with the dough being put into a little warmer place.

Thanks MiceElf - that makes sense.
I've been making all our bread for ages, but husband has just decided he wants to make some, so he's having problems that all beginners have.
Most times the results are good, but this batch is almost inedible.
There are so many variables in breadmaking, it turns out different every time.

I started making bread during the bakers' strike in 1974, it tested so much better than any commercial stuff we continued, although I now use a dough hook to take the really hard work out of it.

It's true that it takes some time to get the hang of it, and of course getting used to your own oven and the vagaries of the weather - temperature and humidity have a significant effect, but in the end it's well worth it. Happy baking.