CLAIM:
Repeatedly boiling tea increases the extraction and concentration of acidic compounds like tannins and polyphenols, thereby lowering its pH and potentially triggering acidity in some people who consume it.
FACT:
Repeatedly boiling tea can increase the extraction of tannins and polyphenols, which are acidic compounds. Experts note that while this may slightly raise acidity, the human stomach usually neutralises it, and the effect is most relevant for individuals with pre-existing acid-related conditions. They also highlighted the need for more large-scale, long-term studies to fully understand the impact of repeatedly boiled tea on digestive health.
Winters are here, and with the nip in the air comes an unbreakable companion for many, a steaming cup of tea. From homes to roadside stalls, our favourite tea vendors keep the kettle on the stove all day, boiling tea again and again to serve a steady stream of customers. But have you ever stopped to think if repeatedly boiling tea could affect your health?
In a viral Instagram reel, educator and content creator Ashu Ghai, with 12 lakh followers, claims that overboiling tea can make it more acidic and may trigger acidity.
To prove this, he prepares tea with just milk and tea leaves, gives it a light boil, cools it, and measures its pH at 6.5, which is slightly acidic. He then boils the same tea again for 15 to 20 minutes. As the colour of the tea darkens, Ashu explains that “boiling the tea again and again leads to two things.” He says that with repeated boiling, tea leaves extract more tannins and polyphenols, which are acidic in nature. “This reduces the pH of the tea and makes it more acidic,” he notes.
He then points out that the pH of the repeatedly boiled tea drops to 5.9. Explaining the second effect, he adds that due to continuous evaporation, there is a loss of water, because of which “the concentration of these chemicals is increasing per unit volume.” He also clarifies that this is not mostly dangerous, but maintains that “boiling the tea again and again does make it more acidic.”
Does repeatedly boiling tea really make it more acidic and trigger acidity?
There are no robust, large-scale studies directly examining the effect of repeatedly boiled tea on acidity in humans.
However, some older research and expert opinions provide insights into the possible mechanisms. An analytical study conducted at the University of Agriculture, Faisalabad, during 1999–2000 investigated the effect of different boiling times and temperatures on tannin extraction from three commercial tea brands. The researchers tested cooking times of 2, 4, 6, 8, and 10 minutes at temperatures of 90°C, 95°C, and 100°C, analysing tannin content and protein solubility.
The study found that “a significant increase in tannin contents and a significant decrease in KoH solubility of protein with increase in time and temperature were recorded.” Higher tannin levels reduced protein digestibility, which can contribute to digestive discomfort. The authors also noted that “the tannin contents increased with an increase in boiling time and protein solubility was decreased with an increase in tannin concentration.”
Highlighting real-world practices, the researchers observed that at public places and roadside tea shops, tea is often “repeatedly and prolonged boiling of tea for maximum extraction of colour and taste,” a practice they warned could be harmful. The study concluded that “two minutes boiling is sufficient for tea making in order to get a good ratio of tannins,” and advised against prolonged boiling to preserve both sensory quality and nutritional safety.
Dr (Prof.) Anil Arora, Senior Gastroenterologist and Hepatologist at Sir Ganga Ram Hospital, explained the science behind this. He said that “by repeatedly boiling the tea, more chemicals like tannins and polyphenols are extracted from the tea leaves. These compounds can irritate the stomach and, being acidic, may increase acidity.”
However, he cautioned that the human stomach has “huge reserves and multiple mechanisms to neutralise acidity,” so whether repeated boiling actually causes harmful acidity is not straightforward. According to him, “to prove this, you would need a trial with about 100 people, comparing tea that is repeatedly boiled versus tea boiled just once over 5 to 10 years. It is not easy to show that this is detrimental.”
Dr Arora emphasised that while repeated boiling plausibly increases acidity, the effect would be most relevant for people with pre-existing acid-related conditions. “People with a tendency for acidity or suffering from acid peptic disease should avoid repeatedly boiled tea. That is the lesson,” he said.
He also noted the challenges in studying this scientifically, adding that “large-scale, long-term studies would be needed, but there are so many other variables like stress, smoking, anxiety, and medications that contribute to acidity. Isolating the effect of repeated boiling alone would be very difficult.”
This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS.
