If someone hands you a cold-brewed coffee and an iced coffee, you’ll be able to taste the difference. The process of determining which you prefer can be as simple as taking two sips. To fully understand why cold-brewed coffee tastes different than iced coffee and other types of coffee that are brewed with hot water, however, we need to delve into the chemistry of making coffee.
Coffee is a Solution of Coffee Solubles and Water
When coffee is brewed, solubles are extracted from coffee beans and dissolved in water, forming a solution. As with any solution, the temperature of the solvent (water) affects how the final solution turns out. In the creation of coffee, varying the temperature of water alters both the brew time and which solubles are extracted.
Brew Time Increases as Temperature Decreases
In general, chemical reactions occur more quickly at higher temperatures. This is why increasing the temperature of the water decreases the brew time of coffee. Typically, coffee is brewed between 195 and 205°F. It takes a few minutes to extract coffee’s solubles at these temperatures. (Espresso is made within the same temperature range but uses pressure to decrease the brew time.)
Cold-brew is an exception. It’s typically made at room temperatures, around 70°F. At this temperature, it takes much longer to extract solubles from the coffee beans. Thus, cold-brews take hours, instead of minutes, to make.
Colder Temperatures Don’t Extract All Solubles
Coffee is complex, containing hundreds of different compounds. As with any compound, the molecules found in coffee extract at different rates and at different temperatures. Some, such as caffeine, are drawn out at both colder and hotter temperatures. Others only become part of the coffee solution if it’s brewed at high temperatures. Even dropping the temperature from 195°F to 156°F will greatly affect certain solubles.
In coffee, the molecules that aren’t extracted at cold-brew temperatures can be categorized into two broad groups: flavorful aromatics and undesirable compounds. Some of the coffee’s most flavorful aromatics are left in the bean during a cold-brew, because the water’s not hot enough to draw them out. Other compounds that produce rancid tastes are also left in the beans, though.
The different extraction results in a completely different taste profile. All of it’s unique characteristics stem from a very simple change that you learned about in high school: changing the temperature of the solvent. As you alter the temperature of water used to make coffee, you’ll change its taste. No other brewing style shows this better than cold-brewing.