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
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
2. Dump in coffee
3. Tie it up
4. Brush off any coffee on the outside of the filter.
Step 3: Start Brewing
Step 4: Let Chill (for a Long Time)
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.