OK, here is my attempt at making hard cider. Keep in mind I am not the expert here, so please watch with that in mind. This show has generated a lot of email....
You don't mention it but did you use any campden tablets? They are used to kill any wild yeast that may be on the fruit at the time of picking. It's pretty much guaranteed that there is wild yeast and bacteria on the fruit including the little bugs that make vinegar. This is probaly why your cider had a vinegar taste. Also if it was me, I would have added sugar to boost the abv (alcohol by volume) Just a few ideas.
try coring the apples first - we find when we make apple sauce that its the seeds & core that make it bitter. Nice color on the cider though, that's why I'm thinking it was the seeds instead of it being vinegared ... I would have thought it would have been more cloudy had it been vinegar. There are several recipes online for making home-made apple cider vinegar in a reused plastic bottle right on your own countertop.
I asked a home winemaker about doing hard cider. He said after it ferments and before you bottle it to add some fresh apple or other juice to sweeten it. And then sulfites or something to stop the fermentation. Anyway, that's supposed to make it taste better.
In the South West of England, the home of powerful but very dry cider, we normal people add a little lime or blackcurrant juice to temper the tartness. It goes down a treat!!!!
Cider, what you call hard cider needs some nitrogen to feed the fermentation, and it was common in Devon and Cornwall to feed it with some meat during the fermentation. Nowadays we add a couple of multivitamin tablets which has the same effect.
Keep up the good work,
Just a couple of comments on the home medicine uses for hard cider (called Scrumpy in the UK). I have tried them both, they work, and I am still here to tell the tale.
1. Hard cider, unlike other alcoholic drinks, is a natural muscle relaxant.
If you get what we call a "frozen shoulder", that is when your Trapezius muscle spasms after moving your arm. It is common after splitting a large stack of logs. It is extremely painful and you feel locked up, but don't worry, hard cider is a very enjoyable cure.
Just drink 4 pints in the late evening, and apart from going to bed very happy, your neck muscles will relax when you sleep. In the morning you will wake up feeling a bit rough around the edges from the cider, but the pain should be gone.
2. If you have a very bad head cold that just doesn't seem to want to go, heat up 2 pints of hard cider and drink it before you go to bed.
Please make certain that you are wrapped up warm in bed as the cider will cause you to sweat out the cold. By the morning you will think you have been walking through a thunderstorm, but your cold should be gone.
If you don't believe me, try it. The worst thing you can get is a hangover!