Once upon a time I was a barista at a little coffee house in New Orleans. They made their cold brew iced coffee by grinding five pounds of coffee into a a large filter bag then soaking it in five gallons of water for 18 hours. What I did is very similar to that, but on a smaller level and probably not up to food service standards.
Step 1: Gathering Supplies
First you'll need a few things to pull this off:
1. Coffee (duh) about 6-8oz for gallon sized container, adjust as needed for your container.
*I don't recommend using espresso grounds like I did here. I wouldn't go with anything darker than French Roast
2. Big filter, I used an old, but clean t-shirt
3. String, used to tie off the bag so the coffee stays in.
*don't use twist ties, they will most likely rust.
4. Container, I used a margarita mix container because I like margaritas and had a clean one handy
5. Water, of course
6. Room in your fridge
Step 2: Get Filter and Coffee Ready
1.Open up the filter (t-shirt) to allow coffee to be dumped in. If you're using a t-shirt, make sure you have enough extra shirt on the sides to allow you to twist the shirt and tie it off with string.
2. Dump in coffee
3. Tie it up
4. Brush off any coffee on the outside of the filter.
Step 3: Start Brewing
Inspect your filter/t-shirt for leaks. If all is well put the filter in your container and add cool water.
Step 4: Let Chill (for a Long Time)
Now all you need to do is cover your container and let your coffee brew in the fridge. I recommend letting it brew for 18+ hours. That will give you a pretty strong pot of coffee. If you like your coffee on the weak side stop after 10-12 hours. If you want your coffee stronger brew it for 24+ hours.
You can always sample your batch during the brewing to see how much additional time is needed.
After you've waited whatever amount of time you've decided on, pull out your filter and enjoy.