People ask whether coffee is acidic for two very different reasons. Coffee enthusiasts talk about acidity as a desirable flavour, the bright, fruity quality of a good light roast. People with heartburn or sensitive teeth ask because they worry acidity will hurt them. These turn out to be related but separate questions, and much of the confusion around low-acid coffee, cold brew and dark roast comes from mixing them up. This article sorts out what acidity means in coffee, what the measurements show, and how much any of it matters for your body.
Three different meanings of acidic
The first meaning is pH, the chemical scale of how acidic or alkaline a liquid is. It runs from 0 to 14, with 7 neutral and lower numbers more acidic. The scale is logarithmic, so a drink at pH 4 is ten times more acidic than one at pH 5 by this measure. The second meaning is titratable acidity, which measures the total amount of acid present in a drink, including acids that are not releasing their full acidity at that moment. Two drinks can have the same pH but very different titratable acidity. The third meaning is perceived acidity, the sourness or brightness a person tastes. As the research below shows, these three do not always move together.
How acidic is coffee on the pH scale?
A study in Scientific Reports by Rao and Fuller[1] measured light roast coffees from Brazil, two regions of Ethiopia, Colombia, Myanmar and Mexico, brewed both hot and cold with the same ratio of coffee to water. The pH values of all the samples ranged from 4.85 to 5.13. That is mildly acidic, in the same broad region as many everyday foods, and far less acidic than many popular drinks.
For comparison, Reddy and colleagues, in the Journal of the American Dental Association[2], measured the pH of 379 commercially available beverages in the United States, including juices, sodas, flavoured waters, teas and energy drinks. Of those, 93% had a pH below 4.0, and 39% were below 3.0, which the authors classified as extremely erosive to teeth. Only 7% had a pH of 4.0 or higher. Brewed black coffee, at around pH 5, sits on the less acidic side of that range.
Is cold brew less acidic?
Cold brew is widely marketed as less acidic, and many people say it is gentler on their stomach. The measurements tell a more specific story. In the study by Rao and Fuller[1], the pH of cold brew and hot brew coffees was comparable, so cold brew was not meaningfully lower on the pH scale. However, the hot brew coffees had higher concentrations of total titratable acids than their cold brew counterparts, and also higher antioxidant activity. The authors suggested that hot brewing extracts more of certain acids that do not fully register on a pH meter.
An earlier study by Fuller and Rao[3] looked at how brewing time, roast and grind affected cold brew. They found that the pH and concentration of a major chlorogenic acid, 3-CGA, were comparable between cold and hot brews, and concluded that any difference in cold brew acidity was likely not due to chlorogenic acid or caffeine. They also found that caffeine and 3-CGA reached equilibrium in cold brew within 6 to 7 hours, faster than the 10 to 24 hours often recommended, and that caffeine concentrations in coarse-ground cold brew were substantially higher than in the matching hot brew.
That study has two practical lessons for anyone making cold brew at home. Grind size did not significantly change how much caffeine or chlorogenic acid ended up in the cold brew, so a coarse grind, which is easier to filter, does not produce a weaker brew in those terms. And because those compounds reached equilibrium after about 6 to 7 hours, steeping far longer mainly changes flavour and convenience rather than extracting much more caffeine or chlorogenic acid. Longer steeping may still affect other flavour compounds that the study did not measure.
So the marketing is partly right and partly wrong. Cold brew does contain fewer total acids than hot coffee made the same way, which may explain why some people find it smoother. But it is not lower in pH, and it can contain more caffeine, which matters for anyone whose stomach reacts to caffeine rather than to acid.
Does roast level change acidity?
Roasting transforms the chemistry of coffee beans, and it affects acids in different directions. Rune and colleagues, in Current Research in Food Science[4], measured acids in French-press specialty coffees roasted from light to very light, using beans from Brazil, Bolivia and Kenya. As roast degree increased, citric, malic and chlorogenic acids decreased, while acetic, lactic, phosphoric, quinic and glycolic acids increased. Sugar content also fell with darker roasting.
So a darker roast is not simply less acidic across the board. Some acids break down while others form. What does change reliably is the balance, and the loss of chlorogenic and citric acids, which are closely linked to the bright acidity of lighter roasts, helps explain why darker roasts taste less sour.
Why dark roast may be gentler on the stomach
The stomach does not react to coffee simply because coffee is acidic. Coffee stimulates the stomach to produce its own acid, which is far stronger than anything in the cup. That is where roast level appears to matter in a different way. Rubach and colleagues[5] gave nine healthy volunteers two coffees with similar caffeine content: a medium roast market blend and a dark roast blend. The dark roast contained more N-methylpyridinium, a compound formed during roasting, at 87 mg per litre compared with 29, and much less chlorogenic acid, 323 compared with 1,126 mg per litre. The dark roast stimulated gastric acid secretion less effectively than the medium roast.
This was a small study measuring acid secretion rather than symptoms, and the authors called for further research. But it suggests that if a dark roast feels easier on the stomach, the reason may be less about the coffee's own acidity and more about compounds that influence how much acid the stomach makes.
Caffeine is not the main driver of stomach acid
It is often assumed that caffeine is what makes coffee irritating, and that decaf is therefore gentler. The classic experiment by Cohen and Booth[6] found that decaffeinated coffee produced a maximum stomach acid output of 16.5 mEq per hour, similar to regular coffee at 20.9, and both were much higher than pure caffeine at 8.4, on a cup-equivalent basis. A review by Boekema and colleagues[7] likewise concluded that coffee's effects on the digestive tract cannot be explained by its acidity, volume or osmolality, and that caffeine cannot solely account for them.
That has a practical implication. Switching to decaf may help people who react to caffeine, but it will not necessarily reduce the stomach acid response. And a coffee that measures as low acid in the cup can still trigger the stomach to produce acid, because the trigger is chemical signalling rather than the acid in the drink.
Acidity you taste is not the same as acidity you measure
For coffee lovers, acidity is a flavour. Santanatoglia and colleagues, in Food Chemistry[8], examined specialty and mainstream coffees, roasted differently and brewed eight different ways, and compared chemical measurements with sensory evaluation. Chlorogenic acids had the biggest influence on pH and titratable acidity, while the sourness people actually perceived correlated more with organic acids, suggesting organic acids may predict perceived acidity.
The study by Rune and colleagues[4] adds a twist: when they tested sensory thresholds, most individual acids, including malic, acetic and lactic acid, were present below the concentration at which people could detect them. Only citric acid was clearly present above its detection threshold, and even coffee experts could not correctly recognise acids added to coffee at typical concentrations. The authors concluded that perceived acidity in coffee is more complex than the effect of any single acid.
In other words, a coffee that tastes bright and acidic is not necessarily more acidic by pH, and a smooth-tasting coffee is not necessarily low in acid. Flavour, chemistry and effects on the body are three separate things.
This has a practical consequence for anyone shopping for a gentler coffee. Tasting notes on a bag, such as bright, citrusy or low acidity, describe flavour as perceived by cuppers. They are useful for choosing a coffee you will enjoy, but on the evidence above they are not a reliable guide to the pH of the brew or to how your stomach will respond to it. The coffee's roast level, how it is brewed and how much caffeine it delivers are more concrete things to adjust.
What about teeth?
Dental erosion, the chemical dissolving of tooth enamel, is driven mainly by low pH. The study by Reddy and colleagues[2] used a pH of 4.0 as the threshold below which beverages are potentially erosive. At around pH 5, black coffee is above that threshold, and would be classed as minimally erosive on that basis.
Buffering capacity also matters, meaning how strongly a drink resists being neutralised by saliva. Owens[9] compared several drinks and found that a bottled coffee frappuccino had the highest pH of the drinks tested other than tap water, and the lowest buffering capacity, meaning the lowest erosive potential among them, while an energy drink had the highest buffering capacity. That study tested a sweetened, milky bottled coffee drink rather than black coffee, but it points in the same direction. On this evidence, acidity is not the main dental concern with coffee; the sugar added to many coffee drinks is a more relevant one.
Does acidity cause heartburn?
People with reflux often look for low-acid coffee in the hope it will prevent heartburn. The evidence on coffee and reflux is itself mixed: a meta-analysis by Kim and colleagues[10] of 15 case-control studies found no significant association between coffee and reflux disease, while other large studies have found a small increase. That debate is covered in detail in our article on coffee and acid reflux. What the chemistry here suggests is that the pH of the coffee in your cup is unlikely to be the main factor, since coffee's effect on stomach acid appears to come from compounds that trigger acid production rather than from its own acids.
Why this matters for Filipino coffee
Philippine coffee culture spans a wide range of roasts, from strong, traditionally brewed kapeng barako to the light-roast specialty coffees now common in third-wave cafés, including many in Marikina. Based on the roast research above, a lighter roast will usually retain more chlorogenic and citric acids and taste brighter, and a darker roast will lose some of those acids and taste less sour. Whether one is better for your stomach depends less on how acidic it tastes and more on how your stomach responds to coffee compounds overall, which varies from person to person.
The limits of this evidence
The pH and acid measurements are laboratory chemistry on specific coffees, and results vary with origin, roast, grind, brewing method and ratio. The stomach acid studies are small and decades apart, and they measured acid secretion rather than symptoms. The dental erosion studies tested beverages in the laboratory rather than in people's mouths. No study we found tested whether switching to cold brew or low-acid coffee reduces heartburn in people with reflux.
The practical answer
Coffee is mildly acidic, with a pH around 5, which is considerably less acidic than most soft drinks, juices and energy drinks. Cold brew has a similar pH to hot coffee but fewer total acids, which may make it taste smoother, though it can contain more caffeine. Darker roasts lose some acids and gain others, taste less sour, and in one small study stimulated less stomach acid than a medium roast.
If coffee bothers your stomach, the evidence suggests experimenting with roast level, brewing method, cup size and timing rather than relying on pH alone. For brewing cold brew at home, see our cold brew guide, and for how roasting changes coffee, our guide to coffee roasts. For coffee on an empty stomach specifically, see our article on that question. Nothing here is medical advice.