Apple cider vinegar readiness

In the Summer, I juiced apples and put the juice in a container along with a tablespoon of last year's apple cider vinegar.  Now in mid-winter, it smells quite acidic, and there's a thick layer of slime on top (the mother).

How do you know when it's ready?

I just taste it... If it tastes strongly of vinegar, and hardy of alcohol, then I figure that it's done...

Also, in some cases, the mother falls to the bottom of the bottle when she has used up all the alcohol. I don't always get a mother, but when I do...