I'm about to do the same thing. I'll likely be doing it my next beer brew day.
My plan:
- 1 gallon of apple juice
- 1 bag of frozen mixed assorted berries (bought some fresh from a street-side vendor in California. Blackberries, raspberries, and blueberries. You can use any combo you see fit)
- Some yeast slurry from a Wyeast 1272 (American Ale II) starter I'll have made for that brew day
- Pour apple juice into 1 gallon glass container, leaving room for berries and some headspace for fermentation (you can do it in the bottle it came in... I just like my glass jugs)
- Pull the berries out of the freezer and dump them right in. Freezing them first not only "sanitizes" them but it breaks open the plant cells so you can get at all the juice available.
- Add yeast. I'll just be adding about two tablespoons or so of thick slurry from my starter. You'll be fine with half a pack of dry yeast (US-05, Nottingham) or liquid if you want to spend the few extra bucks (Sweet Cider, Wyeast 1056, Wyeast 1272, Wyeast 1099.) If you want strong, dry cider that's more like Apfelwine (German applewine) then use EC-1118 Champagne or another dry wine yeast.
- Let sit for a few weeks to a month if using the Cider or Ale yeasts. Let it sit for a couple months to half a year if using champagne or wine yeast.
- Bottle it up
I hope that helps. Ask any more questions you may have. People here are friendly and always willing to help.
EDIT: If you end up doing a 5 gallon batch just scale up. 5 gallons of apple juice, probably about 6 pounds of berries, and a full pack of dry yeast or liquid yeast with a 1 liter starter.