Iced tea is a must for hot peaks. Whether the tea is flavoured or plain, we always love it. However, hot water is reputed to be an indispensable criterion for the release of the tea's beneficial molecules. Does iced tea release so many beneficial molecules? Let's go even further: does iced tea bring something more for health compared to hot tea?
But what exactly is iced tea?
Iced tea refers to tea that is cold, but there are many ways to make iced tea:
- You can brew the tea at room temperature for a few minutes to several hours before putting it in the fridge.
- You can brew the tea with cold water in the fridge overnight.
- The tea can be brewed by placing ice cubes on the leaves and letting it melt
I have deliberately ruled out the method where the tea is brewed hot and then put in the fridge. This method requires a first step of heating, which is not the subject of this article, which is only interested in cold brewing methods.
What happens in my glass of iced tea?
The literature on iced tea and diffused molecules is still quite sparse. Studies that have looked at molecules obtained after cold infusion of tea include Lantano et al. and Castiglioni et al. in 2015.
Another story of antioxidant molecules!
Lantano and his collaborators brewed black teas, oolong teas and green teas either cold (4°C for 12 hours, or a good night's sleep, the time to drink your morning tea and come to work) or hot (90°C 3min, 85°C 4min and 75°C 4min respectively).
Molecular analyses of each infusion have shown that cold infusion increases the overall concentration of polyphenols compared to hot infusion (between 6 and 8 mg/g of leaves). In addition, the concentration of EGCG, the polyphenol with one of the most powerful antioxidant potentials in tea, increases with cold brewing (between 2 and 3 mg/g of leaves for green tea and oolong). On the other hand, the concentration of EC, another potent tea polyphenol, was not detected in iced tea (although the amount of EC is zero in black tea and low in oolong in hot infusion).
To understand whether or not cold infusion improved the antioxidant power of tea, the authors measured the "FRAP value", an experimental value obtained when antioxidant molecules are brought into contact with oxidized molecules. The higher the measurement obtained, the more antioxidant molecules are able to counter oxidation. The authors observed that the FRAP value is very slightly higher for iced green tea (1653.5 vs. 1463.1) and iced black tea (1218.8 vs. 1111.8). On the other hand, this value is multiplied by 4 for iced oolong (1278.5 vs. 325.4).
Certainly we have an iced tea potentially more antioxidant, but to what taste?
Just as Lantano et al. Castiglioni et al. were interested in the antioxidant power of cold-infused green and white teas but also in the organoleptic sensations of iced tea, i.e. the perception of the taste of the tea.
To carry out their study, the authors bought white (Bai Mu Dan, White Lung Ching, White Salima Peony) and green (Green Lung Ching, Green Salima Peony) teas that they brewed either hot (70°C for 7 min) or at room temperature (15min to 2h). The authors found that the total amount of polyphenols was higher in tea infused cold for 2h for Bai Mu Dan, White and Green Salima Peony. The amount of polyphenols was no different for White Lung Ching and was lower for cold Green Lung Ching. Moreover, similarly to Lantano et al. they showed that cold infusion for 2 hours increased the antioxidant activity of Bai Mu Dan, White and Green Salima Peony but not Green or White Lung Ching.
These results are in line with those obtained by Lantano et al. but they also suggest that the type of tea could also condition the cold diffusion of antioxidant molecules.
Moreover, the organoleptic analysis carried out on White and Green Salima Peony hot or cold and on a panel of 20 people reveals that the cold infusion would make it possible to obtain a milder liquor with a more varied aromatic profile.
Pleasure and health!
And in practice on health?
Unfortunately, very little data on the health effects of iced tea is reported in the scientific literature.
The high temperature of the tea was for a time the source of a debate on the risks of chronic inflammation of the esophagus (« Barrett’s Esophagus ») and the consequences on the occurrence of esophageal carcinomas. A prospective study carried out from 2004 to 2008 on 50045 people and published by Islami and its collaborators in 2019 looked at the effects of daily consumption of black and green tea at a temperature above or below 60°C on the occurrence of esophageal carcinomas. The authors found that hot tea increased the risk of esophageal carcinomas (particularly for those who drank more than 700mL per day), but this was not the case for tea at temperatures below 60°C.
This dichotomy between hot and cold was also noted for Maufrais et al. in 2018 for mate. Indeed, 33 people consumed cold (3°C) or hot (55°C) maté infusions. 90 minutes after the ingestion of cold mate, the heart rate decreased slightly but catabolism (here lipid oxidation), baroreflexia (the body's reaction to control blood pressure) and energy use increased slightly. In addition, a stronger hypoglycemic action of iced green tea was also reported by Chen et al. in 2019 (summary issued by one of the collaborators, Jiayi Jiang, the same year).
These different data could suggest that cold tea modulates the metabolism of cells, which could be interesting for metabolic disorders such as diabetes or those associated with cardiovascular disorders.
The literature is still too recent and too poorly informed to be able to give an objective opinion on iced tea and health. Nevertheless, the first published results are encouraging, since cold infusions would make it possible to produce a sweet liqueur with a varied aromatic palette and richer in antioxidant molecules such as EGCG compared to hot infusions. Some prospective studies seem to suggest that iced tea could have an interesting effect on metabolic diseases associated with cardiovascular disorders or diabetes. It will take a number of more summers before more data are available!
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