Why Water Temperature Matters

Water temperature is not something most people spend a lot of time thinking about when they set out to make a cup of tea. Most of the time, the water is simply brought to a boil and poured over the teabag (or loose leaves). However, using boiling water can actually significantly impair the flavor of the tea. The reasons for this lie in chemistry.

A cup of tea contains numerous chemical and mineral compounds, among them amino acids, tannins, and aroma compounds. Aroma compounds are particularly important; they are what impart a certain "nose," or bouquet of aromas, to the liquor. These include such distinct olfactory sensations as smoke, fruit, wet grass, and many others. Certain types of tea have higher concentrations of specific compounds than others. For example, green teas--especially Japanese green teas--have high concentrations of amino acids (due to the unique manner in which they are grown and harvested).

The reason water temperature is important is because all of the aforementioned chemical compounds have a certain temperature at which they are destroyed. For instance, green teas are best infused at relatively low temperatures (see below for a rough guide). If the water is too hot, many of the delicate flavors and aromas will be neutralized and will not be present in the infusion. Even more importantly--and this is almost universally true--using water that is too hot, or steeping the tea for too long (which has a similarly deleterious effect) will introduce bitterness into the cup.

But we still haven't answered the question of why boiling water is bad for the flavor of your tea. Isn't this fine for black tea? The short answer is, no. Even though black tea is 100% oxidized, this doesn't mean there aren't valuable components of the overall impression that are damaged by excessive temperature. One of the most important aspects of a tea is invariably its bouquet. With regards to tea, we experience the aroma two ways--via gases that evaporate from the cup and reach our nose directly (orthonasally)and through our palate and the back of our mouth (retronasally). When water is boiled, it no longer contains any oxygen. This impairs the ability of the aroma compounds to form a gaseous state and subsequently be enjoyed by the taster. As well, it tends to dissolve tannins, which not only are an important component of the flavour but also significant in terms of the health benefits of tea. Using boiling water also encourages the formation of a "skin" of minerals on the surface of the tea, which soaks up some of the other chemical constituents of the flavor and dulls them on the palate.

So what are the best temperatures for each type of tea? The answer isn't as simple as you might think. What works for one tea may not work for another. For example, while many black teas--notably Assam teas--are best in water that is almost boiling (but not quite), another black tea, Darjeeling, is best at slightly lower temperatures. In general, however, there are certain characteristics shared by each type of tea that make them best prepared at a certain temperature. Below are some general guidelines.

WHITE/GREEN TEA: 140F-180F (60C-82C)
OOLONG TEA: 180F-200F (82C-93C)
BLACK/PU ERH TEA: 200F-210F (93C-98C)

This is a complex and important topic. For a more in-depth discussion, a good source is Francois-Xavier Delmas' book The Tea Drinker's Handbook.