Iced coffee is created by brewing hot coffee in the traditional manner and then chilling it in the refrigerator or over ice. Caffeine in iced coffee or cold brew, according to some studies, enters the bloodstream, travels to the brain, and increases brain activity, prompting it to release hormones that boost the nervous system, improve mood, and focus. Iced coffee also lessens the caffeine level of coffee, which helps folks who are caffeine sensitive avoid the jitters.