I got lucky and beat deer to my fruit. We actually had 5 apples. Ate one and it was perfectly sweet and tart. I can’t believe my tree is almost 10 YO.

In answer to your original question, no, you can't pick unripe apples and ripen them in the window, although some old fashioned varieties do change flavour somewhat with storage. Fencing the tree off is the only sure way to keep the deer out. A tall cylinder of wire netting and a couple of posts wont break the bank.

Fruits that can ripen off the plant are called climacteric. Those that have to ripen on the plant are non-climacteric. Apples belong to the former.

When it comes to protecting a few fruits on a tree, you can bag the fruits. I use brown paper bags, other people use ziplock bags, footies sold specifically for this use, wire screens, organza, etc.. Depending on what material you use, the bags can also provide protection against insects.

Daren

While apples are technically climacteric, it's not quite as clear cut as the classical definition implies. Bottom line, an immature apple which is not full size is not going to mature on a window sill. And imo the flavour is never as good as tree ripened fruit.

The fence/physical barrier is going to be the best idea for a few years. Some apples get better (usually sweeter) in cold storage (not a windowsill) such as the Arkansas Black (which can be stored for 6 months or longer), or they may start to rot if not consumed in a few days like the cinnamon spice apple.

Unfortunately i am not able to find much on Anna apples. Only that they come from Israel, and are a child of the Golden Delicious. Most summer apples do not store well (with thousands of varieties of apples there are always exceptions), so i would recommend letting them fully ripen on the tree.