I do not have a view of the phosphoric acid.

The apple juice does not have to be freshly pressed. You can use the cartons of fresh squeezed from the supermarket and even the cheap apple juice made from concentrate has some malic content. However, not all apples are created equal and the more sour apples like Granny Smiths are best. You can even have stewed Bramley apples for a desert as it is very difficult to destroy the malic acid that is why it survives in cider vinegar.