the best way is to do the starch test.
when apples are fallen (say about 50% of the apples), depending of the varieties, only 50 to 75 % of the starch is convert to soluble sugar. so we often have to wait 2-3 weeks before crushing .
the best way to know if there're ready is to use iodine. you can ask in a chemistry a solution of :
for 1 litre of solution: 10 g iodine and 40g potassium iodure
the test: pour 2-3 mm of the solution in a plate, cut an apple in the middle and put it in the solution for a few seconds.
if the apples are dark blue: you have starch; if you don't have color: it's mind that the starch is convert.
this is very important to get a clear juice, and control the fermentation.
