The difference in taste between homemade and commercial apple jelly is more pronounced than in any other preserves I can think of. You can choose the apples and therefore the flavor. You don't need any specialized equipment, though you'll see that I use a foley food mill to get rid of the skins, so I can use the pulp that's left over for making apple butter.
I made this jelly from empires, and I haven't seen such a red jelly from apples other than crabapples. The taste is wonderful but lacks a little character, and I think I'll mix northern spies into my next batch. I usually make jelly from cortlands, (which give a beautiful golden jelly), but I didn't get to it before they had all been used up. I got these apples from the farm stand a week ago, but I'm confident you can make jelly from store bought apples.
Many jam and jelly recipes will tell you to mix in some underripe fruit, but apples have so much pectin you don't need to do that.
3 pounds of apples, washed, quartered and cored, but not peeled
3-4 cups of water (see note)
3/4 cup sugar for every cup of extracted juice.
How's that for a list of ingredients? Cut the apples into one inch pieces, and add water. You've apparently got some latitude here. Many books will say 1 cup of water for every pound of apples. Some say to just cover the apples with water. The old Fannie Farmer cookbook says to use 4 cups of water for 3 pounds of apples, and that might be the best advice. I used about 3 1/2 cups of water. Because you're going to cook the apples there will be some evaporation. It's not as exact a science as it seems like it ought to be, and it's a pretty forgiving process.
Bring the apples to a boil and simmer for 20-25 minutes. You want the skins to have pulled away from the pulp, and the pulp to mash up easily with a spoon. Let cool somewhat. Put the cooked apples through a foley food mill if you want to make apple butter from the leftovers, but all you really need to do is mash the apples against the sides of the pan with a spoon (you could try pushing the pulp through a colander if you want to use if for apple butter). The picture below is of all the skins that are left over from 3 pounds of apples.
Make a way for the juice to separate from the pulp. The simplest thing to do is to line a colander or nonreactive sieve with wet cheesecloth (or washed cotton flannel or a washed white cotton tee-shirt- no fabric softener!!). Cheesecloth needs to be in 3-4 layers if you want crystal clear jelly. One layer of the flannel or cotton tee will be enough. You can also buy a nylon jelly bag, not that's not necessary. Pour the pulp into the colander and let it drip into the bowl for a few hours or overnight, until it's not dripping very often. DO NOT press on the pulp to get more juice out if you want a nice clear jelly.
You should have collected 3-4 cups of juice. Measure into a nonreactive saucepan - at least 2 quarts in size and preferably bigger. Add 3/4 cups of granulated sugar for every cup of juice. Heat on medium high until it starts to boil, and then pay very close attention to it, both because you want to catch the jelly point, and also because as it nears the right temperature it will boil up and double in size, and maybe boil over and make a real sugary mess (not that I've ever done that). Be prepared to pick up the pan if the jelly climbs too high up the sides. This is why you need a big pan.
If you've got a candy thermometer then do use it. Attach it to the side of the pan, and watch as it approaches 220, which is theoretically the jelly point. But you also need to do the "jelly test," which involves swirling some juice in the spoon until it cools for a few seconds, holding it up and watching as the juice drips off the spoon. At first it will drip in single drops. As you approach the jelly point it will come off in two drops (isn't that weird?). Then very soon it will come off in a little sheet that will break away from the spoon. Take it off the heat immediately. I decided this jelly was ready to come off the heat at about 216 because of the way it was starting to sheet from the spoon. It is very tender jelly and took a full 24 hours to jell. It would have jelled sooner if I'd let it cook to 220, but wouldn't have been as tender. What this means is that you don't really need a thermometer - you can just use the jelly test.
As soon as you take it off the heat skim the foam that has collected on the surface. You can skim while you're cooking if you want, but there will be some at the end, too (the skimmings are edible - in fact my favorite). If you don't skim it the foam will mix in with the jelly and look really odd, suspended in spots all through the jelly. Of course if that appeals to you...
You should have already washed jars. It's a good idea to sterilize them (run through the dish washer or fill with water in a pan and bring to a boil), and it's a good idea to process the jars of jelly if you want to keep them at room temperature, but I'm not giving directions for that because it's more complicated and making the jelly is really simple. Pouring the very hot jelly from a clean cup into the jars and putting in the fridge will keep the jelly as long as opened jelly will keep. If you're using canning jars you can cover with a new lid, screw the band on tight, invert the jar briefly so the hot jelly will kill any bacteria or mold on the lid, and the lid will seal and probably give you a little longer life. Still a good idea to keep in the fridge. Chances are the jelly is going to disappear long before you have to worry about it.
This batch made 3 1/2 cups of jelly and should have made a little more than that. Probably could have used a little more water in the apples originally. No problem.
If you've put the pulp through a food mill or a colander and the pulp looks good, you can turn it into apple butter. I like my apple butter to taste of apples, so I just add sugar to taste and a dash of cinnamon (1/4 tsp for this batch) and bring it up to as hot as I can before it starts to explosively bubble (190-200 or so), put in jars and refrigerate. The apple butter is relying on the thickness of the pulp as well as the residual pectin to give you a pleasing spread. But you're not counting on the science of the jellying point, so you can vary your recipe, add more spices, add vinegar, cook it for a long time until it's dark and deep in flavor. You can also use noncaloric sweeteners instead of sugar, which is not something you can do with the jelly, where you're relying on the interaction of the sugar, acid, and pectin, to create a jell. With apple butter the flavor and the thickness are all up to you.