David, the "official" test to determine if an apple is ripe is the iodine test. When the apple is ripe, there is no more starch in the flesh and the iodine test stays yellow - while if there is starch, it becomes dark blue or purple. You can use for that test simple iodine tincture easily bought at the pharmacy, and with an eye dropper, just drop a drop on the transversally cut apple.
This being said, most cider apples don't ripen very evenly - in other words, part of the crop ripens faster while the rest ripens later. I have also noticed that a tree having a full crop will start dropping fruit earlier than another one of the same variety that has a smaller crop. A full week difference on harvest date between 2 trees of the same variety (but with different loads of apples) is quite usual.
In France they usually make 3 harvests, taking the fruit that is on the ground, and after about half of the crop has fallen naturally, they then shake the trees to provoke falling of the rest of the apples before making the third and last harvest run.
If this can make you feel better, I have now finished harvesting my Bulmer's Norman and Douce de Charlevoix. The Yarlington Mills and Muscadet de Dieppe have started to fall, but it is still too early to take the whole crop (but I keep the drops). Others like Reine de pommes and Coat Jersey haven't yet started to drop. Brown's Apple is on a off year for me, so I can't say - but it usually starts to drop by second week of September and I am normally done harvesting it by the 20-25th of September.
As of "sweating", it won't necessarily increase Brix (or SG) really. However if there is still some starch (which would be shown by the iodine test), this starch will transform into sugar. Also, during that ripening, some work will be done on the pectins. Note that sweating is more important on late varieties. For the September cider (or first season cider) there is no real need for a long sweating. For my part, I am planning to do my first cider pressing by the end of next week. The apples will have had about 10 days of sweating - plenty sufficient for early apples when ambiant temperature is still quite high.
Claude
Jolicoeur OrchardZone 4 in Quebec
Author,
The New Cider Maker's Handbook