The question of whether coffee makes the body acidic is common, often fueled by the experience of heartburn or stomach discomfort after drinking a cup. This concern links the beverage’s perceived sourness to a fear of altering the body’s overall internal balance. Addressing this requires examining coffee’s chemical properties and understanding the sophisticated physiological systems humans use to maintain a stable internal environment. This analysis differentiates between coffee’s effects on the digestive tract and its non-existent influence on the body’s systemic acid-base balance.
The Measured Acidity of Brewed Coffee
Coffee is chemically an acidic beverage, typically ranging from pH 4.85 to 5.10. This moderate acidity originates from the dozens of organic acids naturally present in the coffee bean and extracted during brewing. The most abundant compound is chlorogenic acid, which makes up a significant portion of the green bean’s dry weight.
During roasting, chlorogenic acids break down to form other compounds, notably quinic acid, which contributes to the coffee’s flavor profile. Other acids contributing to the overall pH and flavor include citric, malic, and acetic acids. The concentration of these acids is influenced by the bean’s origin, roast level, and brewing method.
How the Body Maintains pH Balance
The human body maintains tight control over its systemic pH through a process known as acid-base homeostasis. Normal blood plasma pH is held within the narrow range of 7.35 to 7.45, which is slightly alkaline. This stable environment is necessary because the structures of proteins and enzymes, which drive metabolic reactions, are highly sensitive to pH fluctuations.
The body employs multiple mechanisms to prevent dietary intake from disturbing this balance. The first line of defense is the chemical buffer systems, such as the bicarbonate buffer system, which immediately absorb or release hydrogen ions to minimize pH change. This instantaneous action occurs in the blood and other extracellular fluids.
The second regulatory system involves the lungs, which control the amount of carbon dioxide (CO2) in the blood. Since CO2 combines with water to form carbonic acid, the respiratory system can rapidly adjust the acid load by increasing or decreasing the rate of breathing. For long-term adjustment, the kidneys provide the third major control mechanism. They regulate the excretion of hydrogen ions into the urine and reabsorb bicarbonate ions back into the bloodstream. These layered systems ensure that consuming an acidic beverage like coffee does not lead to systemic acidosis.
Differentiating Systemic and Gastric Acidity
The misconception that coffee makes the body acidic confuses the beverage’s chemical properties with the body’s physiological response. Coffee does not cause metabolic acidosis because the body’s blood pH remains stable at 7.40, thanks to homeostasis.
The “acidic feeling” associated with coffee is a local effect on the digestive system. The stomach is already highly acidic, with a resting pH between 1.5 and 3.5, due to the secretion of hydrochloric acid (HCl). Coffee can stimulate the production of more stomach acid by triggering the release of gastrin, a hormone that signals the stomach to secrete HCl. This stimulation occurs through compounds like caffeine and certain polyphenols activating receptors in the stomach lining.
Coffee may also contribute to gastroesophageal reflux disease (GERD) symptoms by relaxing the lower esophageal sphincter (LES). The LES is the muscle that acts as a valve between the esophagus and the stomach. When it relaxes, the stomach’s powerful acid can splash back into the less-protected esophagus, causing the burning sensation known as heartburn. This localized irritation is the source of discomfort, not a change in the body’s overall pH.
Practical Ways to Reduce Coffee’s Local Irritation
Since the concern focuses on localized gastric discomfort, several practical adjustments can mitigate coffee’s irritant effects. The roast level significantly impacts acid concentration; darker roasts are gentler on the stomach. The longer roasting process breaks down more chlorogenic acids, resulting in a slightly higher pH and lower perceived acidity.
The brewing method offers another effective avenue for reduction, with cold brewing being the most impactful. Because cold water extracts fewer acidic compounds, cold-brewed coffee can have a noticeably lower total acidity compared to hot-brewed coffee, sometimes by as much as 70%. Additionally, adding milk or creamer can help, as dairy proteins, such as caseins, can bind to some acids, offering a neutralizing or buffering effect in the stomach.