The pH scale is a scientific measurement used to determine how acidic or alkaline a substance is. The scale runs from 0 to 14, where a value of 7 is considered neutral, with pure water serving as the standard. Any substance measuring below 7 is considered acidic, while those above 7 are classified as alkaline, or basic. When considering this chemical measurement, the direct answer is that coffee is an acidic beverage.
The Specific pH Range of Coffee
The typical pH range for a cup of black brewed coffee falls between 4.85 and 5.4, placing it firmly in the moderately acidic category. This liquid is much closer to neutral water at 7.0 than many other common beverages. For comparison, popular sodas often have a pH near 2.5, and orange juice measures between 3.3 and 4.0, making them significantly more acidic than coffee. This moderate acidity level influences both the taste profile and potential digestive effects. The final pH of a brew is not a fixed number and can be influenced by the bean type and the method of preparation.
The Chemical Sources of Coffee’s Acidity
The acidity in coffee originates from a complex mixture of natural organic compounds found within the bean, primarily a group of molecules known as Chlorogenic Acids (CGAs). These CGAs are esters formed from quinic acid and various phenolic acids, and they are highly abundant in the raw, green coffee bean. The roasting process acts as a catalyst, dramatically altering the chemical structure of these acids.
During roasting, the intense heat causes a significant breakdown of the CGAs. This degradation produces a number of other compounds, notably quinic acid and caffeic acid. While the overall concentration of the initial CGAs decreases, the resulting quinic acid contributes to a perceived bitterness and astringency in the final cup. This is often the source of the sharp taste that some drinkers associate with an upset stomach.
Other organic acids also contribute to the flavor profile, including citric acid and malic acid. These compounds are responsible for the bright, fruity, or tangy notes prized in high-quality, lightly roasted coffees. Certain low molecular weight acids, such as formic and acetic acid, can increase in concentration during the roasting process. The delicate balance and transformation of all these acids determine the full chemical complexity of the brewed beverage.
Adjusting Coffee Acidity for Comfort
For those who experience discomfort from coffee’s natural acidity, several practical methods can be used to temper the brew.
Brewing Method and Roast Level
One of the most effective techniques is cold brewing, where coarse grounds are steeped in cold water for an extended period. This method results in a lower acid extraction, producing a final beverage with a higher pH (5.40 to 5.63) compared to a hot brew (4.85 to 5.13). The roast level of the beans also plays a significant role in managing acidity. Darker roasts are generally less acidic because the prolonged exposure to high temperatures breaks down a greater amount of the acidic compounds.
Additives and Filtration
Additionally, the simple act of adding milk or creamer can act as a buffer, with the dairy proteins neutralizing some of the acids. This effect can raise the pH of a mixed drink, such as a cappuccino, to a range closer to 6.0 to 6.4. Using a paper filter during brewing traps some acidic oils, and using a slightly coarser grind size can also limit the extraction of acidic compounds. By manipulating these factors, individuals can customize their coffee to a preferred level of acidity.