Green Tea is Sensitive to Heating
Why is 80°C ideal for green tea? If you’ve ever steeped a green tea in water hotter than that, you likely tasted why. You see, the tea you buy in stores isn’t fully shelf-stable. It’s an active food & reacts to its environment. This is why the package usually recommends storing in a cool, dry place, and away from sunlight.
The Iced Green Tea Study
A 2007 study found that changes happen when a green tea is heated above 85°C. Researchers conducted this study to find the ideal temperature to pasteurize a pre-made iced tea. In the US, the pasteurization is generally required for beverages sold in stores. So the researchers wanted to know what was the ideal temperature that could kill bacteria but not affect the drink’s flavor.
The study researched temperatures from 85°C to 120°C and found interesting changes above the lower end of that range. Green tea’s liquor becomes darker & less green, with a deeper yellow color. Did you just check your cup? Are you remembering green teas from long ago?
Why This Happens
This color difference is likely a result of changes in the tannins. The catechins (tannins common to green tea) are what give green tea its aroma and flavor. These convert into new compounds with off-flavors & aromas. Black tea has a different set of tannins and avoids this fate.
To be specific epigallocatechin gallate, epigallocatechin, epicatechin and epicatechin gallate partially epimerized reducing the amount of catechins in the liquor . But more on those green tea tannins in a later blog post.
So remember this next time you steep or reheat a cuppa; nothing higher than 80°C for green tea.