In the heat of the summer sometimes a cool beverage is preferred over a hot one. The versatility of tea allows us to enjoy it either hot or cold. Though tea was traditionally consumed as a hot drink, nowadays, especially in the summer, it's enjoyed cold. With all of the wonderful posts on iced tea as of late, at the peak of the summer, now seems as good a time as ever to discuss the variables affecting the taste of cold water or iced brewed teas.
Although there are countless variables which influence the final product of tea (water, teapot, amount of leaf used, ...), when one is using a cold or iced infusion the following three factors perhaps affect the final liquor the most.
Steeping time is one of the biggest factors in hot brewing, it also plays a big part in cold brewing. The longer the leaves sit in the water the more substances and enzymes secrete into the water, this is true for hot and cold brewing alike. Hot water causes the quick release of more substances, cold water causes the slow release of limited substances. This is why one tea can taste very different when brewed cold rather than hot.
It has often been said that, “there is no or very little astringency” in iced teas. The chemical family of polyphenols cause tea to taste astringent, catechins, tannins, gallocatechins, and teaflavins are the most common polyphenols in tea. These chemical substances contained in the tea leaf leach into cold water much slower than in hot water. It can often take at least 24 hours of cold brewing to achieve a really astringent taste in cold tea, that would only take a few minutes with hot brewing.
It has also been said that, “It felt cool and refreshing”. One of the main chemical compounds effecting the qi of tea is caffeine. Caffeine is extracted quickly when brewing in hot temperatures, but temperatures under 20 degrees C causes very small amounts of caffeine to be released even after very long periods of cold steeping, therefore very little caffeine is extracted compared to hot brewing. Because of this, iced teas are very low in caffeine, their energy feeling 'softer' and 'cooler' than that of hot tea.
Another factor effecting taste is the level of oxidization and leaf variety. There are three different varieties of camellia sinensis: the large leaf Assam variety, the medium leaf Cambodian variety, and the small leaf Chinese variety. Usually, but not always, the larger the leaf, the stronger the level of caffeine and tannins.
The amount of oxidization the leaves undergo also play an important roll, especially in brewing cold tea. If the oxidization is high such as in the black teas of China, the chemical compounds of the leaf are released faster than in a low oxidized tea such as a Japanese green. Because of this, large leaf, highly oxidized teas require shorter cold infusion times compared to small leaf, non-oxidized teas.
Whether the dry leaf is crushed or non-crushed also effects the cold brew. The damage caused by crushing the dry leaves creates pathways for which the chemicals contained in teas can escape much faster. In this way crushed teas also need less steeping time in cold water.
Much of the above is nothing new, and is often discussed in reference to hot teas, but the slow motion of cold brewing allows one to look at tea brewing in a different light and to enjoy a very different experience with the same leaves. What factors do you feel affect the taste of cold tea? What are some of your experiences with it?