The short version. Almost every cup of coffee on earth sits between pH 4.85 and 5.13, whatever the origin and however you brew it, on the measurements Niny Rao and Megan Fuller published from Thomas Jefferson University in 2018. What people are buying when they search for "low acid coffee" is a dark roast. Roasting breaks down the chlorogenic acids and the C5HT waxes that switch stomach acid on, and builds up a compound called N-methylpyridinium that switches it down. The price is that a French roast tastes of the roaster, not the farm. There is a second route: origins that start gentle before the roaster does anything. Zambia is one of them.
In April 2026 a class action was filed in the United States over Trader Joe's Low Acid Dark French Roast. The complaint, as reported by Daily Coffee News, says the coffee brewed to the label's instructions averaged pH 5.44, which it calls marginally less acidic than ordinary coffee, and that it carried less caffeine than advertised. That is a lawsuit, not a verdict, and the company will have its say.
It is still a strange product to sue over, because the phrase on the bag was always doing more work than the chemistry.
Coffee is not very acidic
Start with the number. In 2018 two chemists at Thomas Jefferson University in Philadelphia, Niny Rao and Megan Fuller, measured the pH of six light-roast coffees from Brazil, two regions of Ethiopia, Colombia, Myanmar and Mexico, brewed hot and brewed cold. Every sample fell between pH 4.85 and 5.13. The hot brews ran from 4.85, an Ethiopian from Ardi, to 5.10, the Brazilian; the cold brews sat a touch higher, from 4.96 to 5.13.
That is a narrow band, and a mild one. Most fruit juices and soft drinks are considerably more acidic than any coffee in that study.
So when a coffee drinker says a cup is "acidic", they are almost never talking about pH. They are talking about perceived acidity: the lemon in a washed Ethiopian, the blackcurrant in a Kenyan, the sensation the specialty trade calls "bright" and a casual drinker calls "sour". Same sensation, two vocabularies. Perceived acidity comes from the mix of acids in the cup, citric, malic, quinic, phosphoric and the chlorogenic family, and from how much of each the brew pulls out. It tracks pH loosely at best.
What your stomach reacts to
The useful work here was done in Veronika Somoza's group at the University of Vienna. In a 2014 paper in Molecular Nutrition and Food Research, Malte Rubach and colleagues gave nine healthy volunteers two coffees with the same caffeine content, a medium-roast market blend and a dark roast, and then measured the acid in their stomachs.
The dark roast was markedly less effective at stimulating gastric acid. The chemistry explains why. Per litre of brew, the dark roast carried three times as much N-methylpyridinium, 87 milligrams against 29, and less of the chlorogenic acids, the C5HT waxes and the trigonelline that the medium roast still held.
Those are the levers. Chlorogenic acids and C5HTs push stomach acid up; in the same group's earlier cell work, chlorogenic acid and caffeine raised the proteins that drive acid secretion. N-methylpyridinium, which does not exist in green coffee and is manufactured by roasting, pushes the other way. Caffeine is a fourth lever, but it cannot be the main one: decaf gives plenty of people heartburn.
Roasting moves the big levers in the gentle direction at once. Which is why the "low acid" shelf looks the way it does.
So "low acid" means "dark roast"
Look at the brands. Puroast, the most visible low-acid name in the United States, claims a brewed pH of 5.7 to 5.9 and about 70 per cent less acid than ordinary coffee; its flagship is a French roast. Trader Joe's sells the low-acid French roast that ended up in court, made with a steam treatment before roasting. Folgers sells Simply Smooth, roasted, it says, for sensitive stomachs.
None of this is new. J.J. Darboven of Hamburg registered the name Idee Kaffee in 1915 and put the coffee on sale in 1927, after Professor Karl Lendrich of the city's Hygiene Institute developed a high-pressure steam process to strip the irritants out of the green bean. Germany was selling stomach-friendly coffee seventy years before anyone typed the phrase into a search box.
What you give up
A French roast is a roast profile with the origin sanded off. The sugars have caramelised past sweetness into bitterness, the volatile aromatics that carry fruit and flowers are gone, and what remains is smoke, cocoa and body. That is a legitimate thing to want. It is also the same cup whether the beans came from Kasama or Colombia.
If you want to taste a farm, the dark-roast route to gentleness closes that door.
Cold brew will not rescue you
The Rao and Fuller study was designed to test cold brew, because vendors sell it as far less acidic. The pH values came out comparable to hot brew. The hot brews did carry more total titratable acid, so cold brew is somewhat gentler in the cup, and some drinkers notice the difference. But the "half the acid" claim does not survive a pH meter.
The other route: origins that start gentle
Go back to that study. In the same lab, with the same roast level and the same water, the Brazilian sat at pH 5.10 and the Ethiopian at 4.85. Before a roaster touches a bean, where it grew and what variety it is have already set the baseline.
Three things push a coffee towards brightness: high altitude, certain varieties, and washed processing that strips the fruit and leaves the acids exposed. Kenya has all three. Its best coffee grows at 1,400 to 2,000 metres, in Nyeri mostly between 1,600 and 2,000, on SL28 and SL34, fully washed. The result is the most electric cup in Africa and the one most likely to bother a sensitive stomach.
Kasama has one of the three, and part of a second. The estates wash most of their coffee, with natural and honey lots on the side, but they sit on a plateau at 1,300 to 1,400 metres (Kateshi at 1,300, Ngoli at 1,400, on the importer Covoya's profile), and much of the planting is Catimor 129, Castillo and Java rather than SL28. Lower and on different trees, the cup comes out the way the green trade has described it for years: balanced and less bright and acidic than other East Africans, in Sweet Maria's words; delicate acidity, a very silky mouthfeel and a finish that settles toward chocolate, in Coffee Review's.
Now the part against our own interest. We have not sent our roast to a laboratory. Our 1 kg bag says "low-acid, gently balanced" on the front, and that line is ours. The tasting note is fair. The word "low-acid" is a claim we have not measured, and writing this piece has made me uncomfortable with it. A bench pH meter and an afternoon would settle the question, and until we have done that, read the bag's "low-acid" as a description of the cup, which is smooth and chocolate-forward with gentle citrus, and not as a laboratory result.
If coffee bothers you
Choose a medium roast of a gentle origin before you choose a French roast of anything; you keep the flavour and get most of the benefit. Buy whole bean and grind coarser rather than finer, since over-extraction pulls more acid. Milk buffers acid, which is one reason a flat white sits easier than an espresso. Drink it with or after food rather than on an empty stomach. And if reflux is a regular feature of your mornings, that is a conversation for a doctor, not a coffee roaster.
Smooth by origin, not by roast.
Shop the Zambian single origin
More from this series: the plateau where this coffee grows and the two dates on every bag of coffee.
Frequently asked questions
Is coffee very acidic? No. Brewed coffee measures between about pH 4.85 and 5.13, milder than most fruit juices. "Acidic" in coffee usually means bright-tasting, not low pH.
Is dark roast better for acid reflux? For many people, yes. Roasting reduces the compounds that stimulate stomach acid and creates one that suppresses it. The trade-off is flavour: a dark roast tastes of the roast, not the origin.
Is cold brew less acidic? Only slightly. In peer-reviewed testing, cold and hot brews of the same coffee had comparable pH; hot brew carried somewhat more total acid.
Is Zambian coffee low acid? It is a naturally gentle, low-brightness cup because of where and on what varieties it grows. We have not lab-tested our roast, so we treat "low-acid" as a tasting description rather than a measurement.
Sources
Rao, N. Z. and Fuller, M., "Acidity and Antioxidant Activity of Cold Brew Coffee", Scientific Reports 8:16030, October 2018. Rubach, M. et al., "A dark brown roast coffee blend is less effective at stimulating gastric acid secretion in healthy volunteers compared to a medium roast market blend", Molecular Nutrition & Food Research 58, 2014. Rubach, M. et al., "Time-dependent component-specific regulation of gastric acid secretion-related proteins by roasted coffee constituents", 2008. ChemistryViews, "Is Coffee Giving You Heartburn? Try a Darker Roast!", April 2022. Daily Coffee News, "Lawsuit Says Trader Joe's 'Low Acid' Coffee Was Too Low on Caffeine", 28 April 2026; ClassAction.org on the same complaint. J.J. Darboven, company history (Idee Kaffee, 1915 and 1927; Karl Lendrich). Puroast product pages; Folgers, "Simply Smooth"; Trader Joe's Low Acid French Roast product listings. Covoya Coffee, Zambia estate product pages (Kateshi and Ngoli altitudes and varieties). Sweet Maria's Coffee Library, Zambia overview. Coffee Review, review of a Zambian coffee from The Roasterie. Kenyan altitudes: Green Plantation, "All about coffee from Kenya"; Ozone Coffee, "SL28".