Whether they’re waking up at D-Hall, preparing for epic study sessions, or stopping for a break before class, campus Spiders are often fueled by coffee. As International Coffee Day rolls around on Oct. 1, chemistry professor Kristine Nolin explained the science behind the daily grind. 

What’s the ideal temperature for brewing coffee? Should the water be boiling? 

The science of the perfect brew of coffee is very complex. However, the magic temperature for coffee across the board is 205 degrees Fahrenheit. This is significantly lower than the boiling point of water, which is 212 F. At 205 F, the ideal extraction of flavor and scent molecules from the coffee into the water is achieved. At higher temperature, the amount of bitter flavor will increase due to more of the flavor molecules being rapidly extracted. Overboiling the water prior to brewing your coffee will lead to deoxygenation of the coffee, which also causes a bitter flavor. 

Cold temperatures have the opposite effect and will slow down the rate of the extraction of the coffee flavor and scent molecule. To achieve the desired flavor, the coffee and the water need to mingle for longer. If a cold brew is done too quickly, a watered-down, sour flavor will be experienced.

Why does coffee solidify at the bottom when it sits too long?

Coffee contains substances suspended in a solution. Specifically, coffee beans release some solids that are washed into the liquid coffee during brewing. These are mostly coffee bean fibers and proteins. These solids have specific functions that add to your experience. They hold on to scent and flavor molecules and release them as you swallow. They also help prevent the coffee from becoming too acidic through a process called buffering. This lessens the impact of the naturally present acids in coffee. As the coffee cools, the solids do not stay suspended in the liquid as well and begin to form a solid layer on the bottom of your coffee cup. Try reversing the process by reheating the coffee and giving it a stir. Did the solids resuspend in the liquid?