Cold brew coffee has recently become a go-to option at coffee shops, due in part to marketing campaigns that note its smoother, less bitter taste. Not to mention that in the summer, this is a popular option when coffee lovers need their daily coffee but want to avoid the excess heat. Unlike coffee brewed relatively quickly at hot temperatures, cold brew is brewed slowly at low temperatures, with the coffee steeping longer within the water. Various health claims have been made about cold brew coffee, some by coffee enthusiasts and others by popular coffee companies, but not much is known about cold brew, and not enough information is out there yet to verify these claims.
Researchers at Thomas Jefferson University in Philadelphia, PA, wanted to collect some information about cold and hot brew coffees, to see if any of the claims made by bloggers, magazines, coffee companies, among others, may actually be true. They wanted to know how the acidity and antioxidant activity of cold brew coffee compared to that of traditionally brewed hot coffee. Antioxidants are compounds found naturally in fruits and vegetables, that prevent a process known as oxidation. Oxidation would commonly produce compounds called free radicals, which can trigger damage to cells in the body. For this study, the researchers used a variety of pre-ground light roast coffees from Brazil, Ethiopia (Ardi and Yirgz), Colombia, Myanmar, and Mexico, all purchased from a commercial vendor.
They freshly brewed coffee for each experiment, using the same coffee to water ratio in both cold and hot brewed coffees. For cold brew, they simply added 35 grams of coffee to 350 mL of filtered water in a mason jar and brewed for 7 hours at room temperature before filtering through a paper coffee filter. For hot brew, they boiled the water, then added the same ratio of coffee grounds to water to a French press carafe and brewed for 6 minutes before filtering through the same type of paper coffee filter.
With hot brew coffee, the researchers measured the pH with a standard pH meter, and found values ranging from 4.85 (Ethiopian coffees) to 5.10 (Brazilian coffee). To determine the amount of acids in each coffee, they titrated (slowly mixed) the hot brew coffee with sodium hydroxide to pH 6 and pH 8. The amount of acids in coffee could influence the level of bitterness tasted. With this method, the Colombian coffee was found to have the highest amount of acidic compounds at both pH values, while Brazil and Myanmar coffees had the lowest.
Antioxidants were counted using an instrument called a UV-Vis spectrometer. With their method, they compared the coffee sample containing antioxidants of an unknown concentration to standards with known concentrations. The Ethiopian hot brew coffee had the most antioxidant activity, while the lowest again belonged to the Brazilian coffee.
When the researchers switched to the cold brew coffee, pH ranged from 4.96 (Ethiopian) to 5.13 (Myanmar), which was quite comparable to the hot coffee. Colombia again had the highest concentration of total titratable acids at pH 6, but the Brazilian coffee had the highest at pH 8. Of these, Ethiopian-Ardi had the highest antioxidants, and Myanmar and Ethiopian- Yirgz had the lowest.
Overall, the water temperature had a strong influence on acidity and antioxidant activity. pH for both cold and hot brew were very similar. The researchers found that while hot coffee had more acidity by the titration method than cold brew, the hot coffee also had higher antioxidant activity. While this study showed that hot brewed coffee was more acidic, the researchers suggest that these acidic compounds might be responsible for the higher antioxidant levels. For all the coffee lovers out there: more work needs to be done to assess the health benefits of drinking hot coffee compared to cold brew coffee. Scientists don’t yet know the health effects of coffee when brewed at different temperatures or times, or how the antioxidant level in cold brew influences any of the protective benefits previously known to be associated with hot brew. In the meantime, whether you enjoy your coffee brewed hot or cold, enjoy the flavor and extra boost of energy that it gives!