There are hundreds of flavor components in coffee — when coffee is heated, different flavors come forward. Depending on how long a bean is roasted, you can end up with different profiles, suiting different palates. Dark roasts, like the King Bean French Roast, will be roasted up to 450 degrees Farenheit (it's so dark the beans almost smell burned). A medium to light roast will reach 410 degrees, and somewhere in between, like an Italian, will get up to 430 degrees. You can, in theory, use any beans to make cold brew — you're still roasting and grinding. But because heat is never added during the brew, if you use a super light roast, you won't end up with a very full-bodied or strong finished product. Medium roasts are ideal for the cold brew process.
Iced coffee is simply hot coffee that has been chilled and poured over ice. It can often be more muted than its full-bodied cold brew sister, due to the addition of water (ice), which dilutes the beverage.
Cold brew coffee is made with coffee grounds and water without using heat. Grounds (medium to coarse grounds are generally best) are submerged for an extended period of time using cold or room temperature water. More grounds are required and are submerged for longer (than hot coffee) because the low temps mean a longer extraction time. If you let your cold brew steep for an hour, it won't taste like much.
Nitro Cold Brew
First thing's first — all cold brew that is coming out of a tap is using nitrogen, that's what propels it out of the tap and also acts as a preservative. That does not mean it's all nitro cold brew, though. As King Bean's Katie Weinberger explains: "With true nitro coffee, the nitrogen is infused with the coffee in the keg before it even gets on the tap and then when you dispense it, it brings out the nitrogen with it that's already in the coffee." The coffee then comes out of a specific faucet head through five small holes which forces the coffee and nitrogen through at a higher pressure. That's where you get, as Corey Steranka explains, that cascading effect "like a Guinness."