I found a recipe for a yeast bread that I was quite happy with, which starts with the yeast in 2 cups of milk, then uses 1/3 of a cup of honey as the source of sugar. More recently, I came across this BA video on cider donuts which starts out with essentially making mulled apple cider and reducing it to a syrupy/jelly consistency.
This inspired me to try to make an apple cider yeast bread. I found this recipe for an apple cider yeast bread, but it says that it produces a bread with "a hint of apple and a faint sweetness". "A hint of apple" is not enough for me, I really want to make a yeast-based bread that truly tastes of apple.
I substituted 4 cups of apple cider (with cinnamon, cloves, and an allspice berry), reduced to about 1/2 cup, for the honey in the original recipe (I checked, 4 cups of cider has about the same amount of sugar as 1/3 cup of honey).
Unfortunately, my bread came out tasting like a wonderful yeast bread, without the slightest trace of apple (it doesn't taste like the original recipe, I think it's actually better, but no trace of the apple cider). I would like to make my cider bread truly contain a strong apple flavor.
Bread does not have to be made with milk, in fact that is rare - bread is usually made with water. You could substitute apple cider for milk for a much stronger apple flavor, my concern with that approach is the sugar you are adding (apple cider is very sweet) for 2 reasons:
If you want to boost the apple flavor but nothing else your best bet is to add an apple extract of some kind.
I suggest that (in addition to using a reduction of the juice*/cider) you add some solid apple.
Personally I would get dried apple, of a tasty variety if at all possible, and put it through a food processor until fairly fine. I dehydrate my own home-grown apples, selected for flavour, but would buy Cox or Granny Smith for this. Then add as you would other dried fruit. If you get the really dry dried apple chips, you could partially rehydrate the pieces in spiced apple juice/cider to soften it a little, adding to the flavour.
* Where I'm from "cider" is always alcoholic, the unfermented juice is just "juice" even if cloudy, so I'll use both terms, hopefully correctly.
You won't get apple-tasting bread by using apples. What you think of as "taste" is actually the aroma of the apple, and has little to do with the taste buds. A whole fresh apple tastes of apples. If you put pieces of an apple in the dough, it is already a large amount of dough to a smaller amount of apple (your bread would fall apart if you were to use more than 50% apple), and then you bake it, making a large part of the aroma float away and the rest change (baked apples don't taste like fresh apples).
If you try somehow concentrating the apple products before adding them to the bread, you actually fare worse. When you make treacle, or dried apple, or something similar, you retain the solids and let the liquid evaporate. The aroma is dissolved in the liquid, and so you end up with less aroma per gram of apple than in a fresh apple. So it doesn't help for your purpose.
If you go back to the fresh apple example, my mother used to sometimes make a quickbread with quite a bit of grated apple mixed into the batter. The apple aroma was so mild, I sometimes didn't realize if it is apple quickbread or a cake from a similar batter if I didn't pay close attention to the texture. And I had no chance of distinguishing if she used apples or substituted quinces if she didn't tell me. So, even with whole apple pieces, you get a hint, no more.
You can try "cheating", by adding strong aromas which are typically associated with apple. If you add some cinnamon, people who are accustomed to an apple-cinnamon combination will perceive it as more apple-y. But this depends on the eaters' history, and will only take you so far. Another thing that doesn't do quite what you wanted is to drop the bread idea and make apple strudel instead, with a sufficient ratio of filling to dough.
Your only chance for a pronounced apple taste in the bread is to get some concentrated artificial flavoring and add that in the proper amount (which will depend on the actual flavoring agent). All other forms will give you a slight apple hint, not a strong apple taste when baked as a bread or a quickbread.
Do you know about Boiled Cider? Add a dollop into pie or bread; it definitely augments the apple flavour. King Arthur Flour sells some from Vermont.
I've gotten an excellent, cider-y apple taste into muffins. (I know you're making a yeast dough, I believe this same method will work with a yeast dough.) Here's how:
Take some good-flavored ripe apples, put them in a paper bag and close the top. This seals in some of the gas that encourages ripening, while preventing moisture build-up. Let sit out at room temperature for a week or so, to ripen the apples to over-ripe. Check on them occasionally to make sure they're not rotting. Every time you open the bag, it should smell very apple-y (if you have fruit flies around, they will be very interested). If they do start to rot, cut off the rotten parts and use the remainder of the apples immediately. In fact, I've gotten the best results with using the non-rotten half of a half-rotten apple. Do a taste-test on a small sliver to make sure the taste is good.
Once the apples are as ripe as you can get them, you're ready to bake. Peel the apples, and use a grater to shred them coarsely. Mix the shredded apples with brown sugar, and let sit for 10 minutes, or while you prepare the other ingredients for your bread. While they sit, the sugar will draw the juice out of the apple shreds, creating a sugar syrup (this process is called maceration*). That way your finished bread won't have soggy spots in it from the apple shreds. Combine your macerated apples with the wet ingredients, and follow your recipe as usual. I try to estimate the amount of juice released from the apples, and reduce the amount of liquid by that amount.
In muffins, the actual shreds of apple aren't particularly noticeable, either in terms of texture or flavor. Most of the flavor comes of the shreds into the sugar syrup, which mixes into the actual batter, and the whole muffin has a good, apple-y flavor.
*Maceration can be done with salt instead of sugar. If you did it with only salt it would probably be too much salt. But you could use a combination of salt and sugar, if you wanted to limit the amount of sugar. Just use the amount of salt that would normally go into your bread, plus as much sugar as needed.