There are basically two brewing methods in making a good cup of coffee. Hot or cold; and how you brew the coffee can really change how your coffee tastes. A hot-brewed coffee is brewed at high temperature and typically made on the order of minutes. The outcome is coffee with a strong aroma but with a sour or acidic bite.
Cold Brew Coffee is made by soaking coffee grounds in room temperature and steeped, like tea, for 16-24 hours. This process extracts a stronger and smoother coffee. Cold Brew is taking the world by storm because it often has a deeper, less acidic and more subtle taste than a hot-brewed coffee. As a result, Cold Brew Coffee is suitable for people with sensitive stomach and heartburn as the acidity and bitterness is absent.
The Chemistry. When coffee grounds are mixed with water, chemical reactions take place to extract the coffee essentials. Coffee dissolves best 90 to 96 Celsius, so coffee brewed in hot water will give a more full bodied, aromatic and flavorful profile than cold brew. But increased solubility is not always a good thing. Hot-brewed coffee causes the coffee’s chemical compounds to degrade and oxidize, giving the coffee a sour and bitter taste. Because Cold Brew Coffee is brewed below optimal temperature, it has to sit longer to create a strong brew. Whilst oxidation and degradation still happen when coffee is brewed cold, it happens much more slowly. This is why Cold Brew Coffee almost never tastes acidic or bitter. It also stays fresh much longer than hot-brewed coffee.